Center for Biomolecular and Tissue Engineering Pratt School of Engineering Duke University |
||
HOME > pratt > CBTE | Search Help Login |
| Publications of Lori A. Setton :chronological alphabetical by type listing:%% @booklet{Nettles09, Author = {D. L. Nettles and A. Chilkoti and L. A. Setton}, Title = {Early Metabolite Levels Predict Long-Term Matrix Accumulation for Chondrocytes in Elastin-like Polypeptide Biopolymer Scaffolds}, Journal = {Tissue Engineering Part A}, Volume = {15}, Number = {8}, Pages = {2113 -- 2121}, Year = {2009}, Month = {August}, ISSN = {1937-3341}, Abstract = {The development of cartilage tissue engineering scaffolds could greatly benefit from methods to evaluate the interactions of cells with scaffolds that are rapid, are nondestructive, and can be carried out at early culture times. Motivated by this rationale, the objective of the current study was to evaluate whether the concentration of metabolites in scaffold-cell cultures at early culture times could predict matrix synthesis in the same samples at longer culture times. Metabolite and matrix synthesis were measured for 16 different formulations of cell-laden elastin-like polypeptide hydrogels. Metabolites were measured at days 4 and 7 of culture, while matrix accumulation was evaluated at day 28. Four of the 16 formulations resulted in molar ratios of lactate: glucose near 2, indicating anaerobic metabolism of glucose, which resulted in collagen: glycosaminoglycan accumulation ratios near those of native tissue. Lactate and pyruvate concentrations were found to significantly correlate with both sulfated glycosaminoglycan and hydroxyproline accumulation, with better fits for the latter. Lactate was found to be the strongest predictor of both matrix components, suggesting that measuring this metabolite at very early culture times may be useful for evaluating the status of tissue engineering constructs in a rapid and nondestructive manner.}, Key = {Nettles09} } @booklet{Christensen09, Author = {T. Christensen and M. Amiram and S. Dagher and K. Trabbic-carlson and M. F. Shamji and L. A. Setton and A. Chilkoti}, Title = {Fusion order controls expression level and activity of elastin-like polypeptide fusion proteins}, Journal = {Protein Science}, Volume = {18}, Number = {7}, Pages = {1377 -- 1387}, Year = {2009}, Month = {July}, ISSN = {0961-8368}, Abstract = {We have previously developed a method to purify recombinant proteins, termed inverse transition cycling (ITC) that eliminates the need for column chromatography. ITC exploits the inverse solubility phase transition of an elastin-like polypeptide (ELP) that is fused to a protein of interest. In ITC, a recombinant ELP fusion protein is cycled through its phase transition, resulting in separation of the ELP fusion protein from other Escherichia coli contaminants. Herein, we examine the role of the position of the ELP in the fusion protein on the expression levels and yields of purified protein for four recombinant ELP fusion proteins. Placing the ELP at the C-terminus of the target protein (protein-ELP) results in a higher expression level for the four ELP fusion proteins, which also translates to a greater yield of purified protein. The position of the fusion protein also has a significant impact on its specific activity, as ELP-protein constructs have a lower specific activity than protein-ELP constructs for three out of the four proteins. Our results show no difference in mRNA levels between protein-ELP and ELP-protein fusion constructs. Instead, we suggest two possible explanations for these results: first, the translational efficiency of mRNA may differ between the fusion protein in the two orientations and second, the lower level of protein expression and lower specific activity is consistent with a scenario that placement of the ELP at the N-terminus of the fusion protein increases the fraction of misfolded, and less active conformers, which are also preferentially degraded compared to fusion proteins in which the ELP is present at the C-terminal end of the protein.}, Key = {Christensen09} } @booklet{Adams09, Author = {S. B. Adams and M. F. Shamji and D. L. Nettles and P. Hwang and L. A. Setton}, Title = {Sustained Release of Antibiotics From Injectable and Thermally Responsive Polypeptide Depots}, Journal = {Journal Of Biomedical Materials Research Part B-applied Biomaterials}, Volume = {90B}, Number = {1}, Pages = {67 -- 74}, Year = {2009}, Month = {July}, ISSN = {1552-4973}, Abstract = {Biodegradable polymeric scaffolds are of interest for delivering antibiotics to local sites of infection in orthopaedic applications, such as bone and diarthrodial joints. The objective of this study was to develop a biodegradable scaffold with ease of drug loading in aqueous solution, while providing for drug depot delivery via syringe injection. Elastin-like polypeptides (ELPs) were used for this application, biopolymers of repeating pentapeptide sequences that were thermally triggered to undergo in situ depot formation at body temperature. ELPs were modified to enable loading with the antibiotics, cefazolin, and vancomycin, followed by induction of the phase transition in vitro. Cefazolin and vancomycin concentrations were monitored, as well as bioactivity of the released antibiotics, to test an ability of the ELP depot to provide for prolonged release of bioactive drugs. Further tests of formulation viscosity were conducted to test suitability as an injectable drug carrier. Results demonstrate sustained release of therapeutic concentrations of bioactive antibiotics by the ELP, with first-order time constants for drug release of similar to 25 h for cefazolin and similar to 500 h for vancomycin. These findings illustrate that an injectable, in situ forming ELP depot can provide for sustained release of antibiotics with an effect that varies across antibiotic formulation. ELPs have important advantages for drug delivery, as they are known to be biocompatible, biodegradable, and elicit no known immune response. These benefits suggest distinct advantages over currently used carriers for antibiotic drug delivery in orthopedic applications. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 67-74, 2009}, Key = {Adams09} } @booklet{Shamji09, Author = {M. F. Shamji and P. Hwang and R. W. Bullock and S. B. Adams and D. L. Nettles and L. A. Setton}, Title = {Release and Activity of Anti-TNF alpha Therapeutics From Injectable Chitosan Preparations for Local Drug Delivery}, Journal = {Journal Of Biomedical Materials Research Part B-applied Biomaterials}, Volume = {90B}, Number = {1}, Pages = {319 -- 326}, Year = {2009}, Month = {July}, ISSN = {1552-4973}, Abstract = {Background: Tumor necrosis factor alpha (TNF alpha) is a cytokine that regulates immune and inflammatory overactivation in various pathological states. Protein therapeutics may antagonize this cytokine, but may also have systemic toxicities. Small molecule natural products are also efficacious, but can suffer from poor oral bioavailability. A drug delivery vehicle is needed to sustain release of active therapeutics and address localized inflammation. Materials: Chitosan is a biocompatible aminopolysaccharide that undergoes thermally-initiated gelation in cosolutions with glycerophosphate (GP.), and may entrap and sustain release of additive therapeutics. Gelation time and temperature of chitosan/GP were evaluated by turbidity (OD350), as was the kinetic effect of bovine serum albumin (BSA) entrapment. We investigated in vitro release of BSA and various anti-TNF agents (curcumin, sTNFRII, anti-TNF antibody) and confirmed in vitro activity of the released drugs using an established bioassay. Results: Turbidity results show that chitosan/GP thermogel achieves gelation at 37 degrees C within 10 min, even with significant protein loading. Sustained BSA release occurred with 50\% retained at 7 days. All anti-TNF therapeutics exhibited sustained release, with 10\% of sTNFRII and anti-TNF antibody remaining after 7 days and 10\% of curcumin remaining after 20 days. After release, each compound antagonized TNF alpha-cytotoxicity in murine fibrosarcoma cells. Conclusions: This study demonstrates that thermogelling chitosan/GP entraps and sustains release of a broad range of anti-TNF agents. Such delivery of disease-modifying therapy could establish a drug depot to treat local inflammation. The breadth of molecular sizes demonstrates significant versatility, and slow release could protect against toxicities of systemic delivery. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 90B: 319-326, 2009}, Key = {Shamji09} } @booklet{Shamji09a, Author = {M. F. Shamji and K. D. Allen and S. So and L. F. Jing and S. B. Adams and R. Schuh and J. Huebner and V. B. Kraus and A. H. Friedman and L. A. Setton and W. J. Richardson}, Title = {Gait Abnormalities and Inflammatory Cytokines in an Autologous Nucleus Pulposus Model of Radiculopathy}, Journal = {Spine}, Volume = {34}, Number = {7}, Pages = {648 -- 654}, Year = {2009}, Month = {April}, ISSN = {0362-2436}, Abstract = {Study Design. The authors investigated gait abnormalities and mechanical hypersensitivity associated with invertebral disc herniation in a rat model of radiculopathy. Further evaluation involved assessing how nucleus pulposus (NP) injury affected systemic cytokine expression and molecular changes at the dorsal root ganglion (DRG). Objective. The objective of this work was to describe the gait and behavioral changes in an animal model of discherniation induced radiculopathy. A second objective included examining how these functional changes correlated with neuroinflammation and autoreactive lymphocyte immune activation. Summary of Background Data. Animal models of radiculopathy describe demyelination, slowed nerve conduction, and heightened pain sensitivity after application of autologous NP to the DRG. The quantitative impact of disc herniation on animal locomotion has not been investigated. Further, while local inflammation occurs at the injury site, the role of autoimmune cytokines reactive against previously immune-sequestered NP requires investigation. Methods. NP-treated animals (n = 16) received autologous tail NP placed onto the L5 DRG exposed by unilateral facetectomy, and control animals (n = 16) underwent exposure only. At weekly time points, animals were evaluated for mechanical allodynia, thermal hyperalgesia, and gait characteristics through digitized video analysis. Serum cytokine content was measured after animal sacrifice, and immunohistochemistry tested DRG tissue for mediators of inflammation and immune activation. Results. Sensory testing revealed mechanical allodynia in the affected limb of NP-treated rats compared with sham animals (P $<$ 0.01) at all time points. Gait analysis reflected functional locomotive consequences of marked asymmetry (P = 0.048) and preference to bear weight on the contralateral limb (duty factor imbalance, P $<$ 0.01) at early time points. Equivalent serum cytokine expression occurred in both groups, confirming the local inflammatory nature of this disease model. Immunohistochemistry of the sectioned DRGs revealed equivalent postsurgical inflammatory activation (interleukin 23, P = 0.47) but substantial early immune activation in the NP-treated group (interleukin 17, P = 0.01). Conclusion. This model of radiculopathy provides evidence of altered gait in a model of noncompressive disc herniation. Systemic inflammation was absent, but mechanical allodynia, local inflammation, and autoreactive immune activation were observed. Future work will involve therapeutic interventions to rescue animals from the phenotype of inflammatory radiculopathy.}, Key = {Shamji09a} } @booklet{Shamji08, Author = {M. F. Shamji and J. Chen and A. H. Friedman and W. J. Richardson and A. Chilkoti and L. A. Setton}, Title = {Synthesis and characterization of a thermally-responsive tumor necrosis factor antagonist}, Journal = {Journal Of Controlled Release}, Volume = {129}, Number = {3}, Pages = {179 -- 186}, Year = {2008}, Month = {August}, ISSN = {0168-3659}, Abstract = {Numerous antagonists of tumor necrosis factor alpha (TNF alpha) have been developed to attenuate inflammation and accompanying pain in many disease processes. Soluble TNF receptor type II (sTNFRII) is one such antagonist that sequesters TNF alpha away from target receptors and attenuates its activity. Systemic delivery of soluble TNF receptors or other antagonists may have deleterious side effects associated with immune suppression, so that strategies for locally targeted drug delivery are of interest. Elastin-like polypeptides (ELPs) are biopolymers capable of in situ drug depot formation through thermally-driven supramolecular complexes at physiological temperatures. A recombinant fusion protein between ELP and sTNFRII was designed and evaluated for retention of bivalent functionality. Thermal sensitivity was observed by formation of supramolecular submicron-sized particles at 32 degrees C, with gradual resolubilization from the depot observed at physiological temperatures. In vitro refolding of the sTNFRII domain was required and the purified product exhibited an equilibrium dissociation constant for interacting with TNF alpha that was seven-fold higher than free sTNFRII Furthermore, anti-TNF activity was observed in inhibiting TNR alpha-mediated cytotoxicity in the murine L929 fibrosarcoma assay. Potential advantages of this ELP-sTNFRII fusion protein as an anti-TNFa drug depot include facility of injection, in situ depot formation, low endotoxin content, and functionality against TNF alpha. (C) 2008 Elsevier B.V. All rights reserved.}, Key = {Shamji08} } @booklet{Shamji08a, Author = {M. F. Shamji and L. F. Jing and J. Chen and P. Hwang and O. Ghodsizadeh and A. H. Friedman and W. J. Richardson and L. A. Setton}, Title = {Treatment of neuroinflammation by soluble tumor necrosis factor receptor Type II fused to a thermally responsive carrier}, Journal = {Journal Of Neurosurgery-spine}, Volume = {9}, Number = {2}, Pages = {221 -- 228}, Year = {2008}, Month = {August}, ISSN = {1547-5654}, Abstract = {Object. Biochemical irritation of the dorsal root ganglion (DRG) after intervertebral disc herniation contributes to radiculopathy through tumor necrosis factor-alpha (TNF alpha)-mediated inflammation. Soluble TNF receptor Type II (sTNFRII) sequesters this cytokine, providing clinical benefit. Previous work involving conjugation of sTNFRII with thermally responsive elastin-like polypeptide (ELP) yielded a chimeric protein (ELP-sTNFRII) with in vitro anti-TNF alpha bioactivity. Furthermore, temperature-triggered ELP aggregation into a "depot" prolongs protein residence time following perineural injection. In this study the authors evaluated the inflammatory phenotype of DRG explants after TNF alpha stimulation, and assessed the abilities of sTNFRII or ELP-sTNFRII to attenuate these neuroinflammatory changes. Methods. Rat lumbar DRGs (35 animals) were treated in 6 groups, as follows: control; TNFa (25 ng/ml); TNFa with low- (0.2 mu g/ml) or high-dose (1 mu g/ml) sTNFRII; and TNFa with low- (52.5 mu g/ml) or high-dose (262.5 mu g/ml) ELP-sTNFRII. After 24 hours, supernatant was evaluated for inflammatory cytokines (interleukin [IL]-1, IL-6, and IL-10); prostaglandin E-2; and metabolites (glutamate, lactate, and pyruvate). Single-factor analysis of variance with post hoc Dunn analysis (alpha = 0.05) was used to assess treatment differences. Results. Incubation of explants with TNFa caused metabolic stress reflected by an increased lactate/pyruvate ratio (1.8 +/- 0.5-fold) and extracellular glutamate (79 +/- 8\% increase). Inflammatory activation was observed with heightened IL-6 release (5.2 +/- 1.4-fold) and prostaglandin E-2 production (14 +/- 3-fold). An autoregulatory response occurred with an 11.8 +/- 0.6-fold increase in sTNFRI shedding. Treatment with high doses of sTNFRII or ELP-sTNFRII reversed all changes. Values are expressed as the mean +/- standard deviation. Conclusions. These results demonstrate that TNFa stimulation of DRG explants yields a phenotype of neurotoxic metabolite release and inflammatory mediator expression. Coincubation with either sTNFRII or ELP-sTNFRII antagonizes TNFa activity to abrogate these changes, suggesting potential for therapeutic intervention to treat peripheral nerve inflammatory disease.}, Key = {Shamji08a} } @booklet{Upton08, Author = {M. L. Upton and C. L. Gilchrist and F. Guilak and L. A. Setton}, Title = {Transfer of macroscale tissue strain to microscale cell regions in the deformed meniscus}, Journal = {Biophysical Journal}, Volume = {95}, Number = {4}, Pages = {2116 -- 2124}, Year = {2008}, Month = {August}, ISSN = {0006-3495}, Abstract = {Cells within fibrocartilaginous tissues, including chondrocytes and fibroblasts of the meniscus, ligament, and tendon, regulate cell biosynthesis in response to local mechanical stimuli. The processes by which an applied mechanical load is transferred through the extracellular matrix to the environment of a cell are not fully understood. To better understand the role of mechanics in controlling cell phenotype and biosynthetic activity, this study was conducted to measure strain at different length scales in tissue of the fibrocartilaginous meniscus of the knee joint, and to de. ne a quantitative parameter that describes the strain transferred from the far-field tissue to a microenvironment surrounding a cell. Experiments were performed to apply a controlled uniaxial tensile deformation to explants of porcine meniscus containing live cells. Using texture correlation analyses of confocal microscopy images, two-dimensional Lagrangian and principal strains were measured at length scales representative of the tissue (macroscale) and microenvironment in the region of a cell (microscale) to yield a strain transfer ratio as a measure of median microscale to macroscale strain. The data demonstrate that principal strains at the microscale are coupled to and amplified from macroscale principal strains for a majority of cell microenvironments located across diverse microstructural regions, with average strain transfer ratios of 1.6 and 2.9 for the maximum and minimum principal strains, respectively. Lagrangian strain components calculated along the experimental axes of applied deformations exhibited considerable spatial heterogeneity and intersample variability, and suggest the existence of both strain amplification and attenuation. This feature is consistent with an in- plane rotation of the principal strain axes relative to the experimental axes at the microscale that may result from fiber sliding, fiber twisting, and fiber-matrix interactions that are believed to be important for regulating deformation in other fibrocartilaginous tissues. The findings for consistent amplification of macroscale to microscale principal strains suggest a coordinated pattern of strain transfer from applied deformation to the microscale environment of a cell that is largely independent of these microstructural features in the fibrocartilaginous meniscus.}, Key = {Upton08} } @booklet{Nettles08, Author = {D. L. Nettles and K. Kitaoka and N. A. Hanson and C. M. Flahiff and B. A. Mata and E. W. Hsu and A. Chilkoti and L. A. Setton}, Title = {In situ crosslinking elastin-like polypeptide gels for application to articular cartilage repair in a goat osteochondral defect model}, Journal = {Tissue Engineering Part A}, Volume = {14}, Number = {7}, Pages = {1133 -- 1140}, Year = {2008}, Month = {July}, ISSN = {1937-3341}, Abstract = {The objective of this study was to evaluate an injectable, in situ crosslinkable elastin-like polypeptide (ELP) gel for application to cartilage matrix repair in critically sized defects in goat knees. One cylindrical, osteochondral defect in each of seven animals was filled with an aqueous solution of ELP and a biocompatible, chemical crosslinker, while the contralateral defect remained unfilled and served as an internal control. Joints were sacrificed at 3 (n=3) or 6 (n=4) months for MRI, histological, and gross evaluation of features of biomaterial performance, including integration, cellular infiltration, surrounding matrix quality, and new matrix in the defect. At 3 months, ELP-filled defects scored significantly higher for integration by histological and gross grading compared to unfilled defects. ELP did not impede cell infiltration but appeared to be partly degraded. At 6 months, new matrix in unfilled defects outpaced that in ELP-filled defects and scored significantly better for MRI evidence of adverse changes, as well as integration and proteoglycan-containing matrix via gross and histological grading. The ELP-crosslinker solution was easily delivered and formed stable, well-integrated gels that supported cell infiltration and matrix synthesis; however, rapid degradation suggests that ELP formulation modifications should be optimized for longer-term benefits in cartilage repair applications.}, Key = {Nettles08} } @booklet{Shamji08b, Author = {M. F. Shamji and L. Whitlatch and A. H. Friedman and W. J. Richardson and A. Chilkoti and L. A. Setton}, Title = {An injectable and in situ-gelling biopolymer for sustained drug release following perineural administration}, Journal = {Spine}, Volume = {33}, Number = {7}, Pages = {748 -- 754}, Year = {2008}, Month = {April}, ISSN = {0362-2436}, Abstract = {Study Design. This study evaluated whether the aggregation behavior of a thermally responsive elastin-like polypeptide (ELP) prolongs protein residence time at the dorsal root ganglion (DRG). This work involves development of a sustained-release drug delivery vehicle to provide high and sustained levels of biologic therapeutics to the dorsal root ganglion while minimizing systemic exposure. Objective. To study the potential of the ELP biopolymer to sustain release and lower systemic exposure of bioactive peptides following perineural administration. Summary of Background Data. Anticytokine treatment for lumbar radiculopathy may offer clinical improvement, but exposes patients to systemic toxicities of immunosuppression. ELPs are environmentally responsive polypeptides that undergo a phase transition on heating to form an insoluble aggregate. Drug conjugates with ELP exhibit both temperature-sensitivity and in vitro bioactivity. Monomer resolubilization yields solution-phase molecules, and this reversible aggregation behavior may create a perineural drug depot to sustain drug delivery to an inflamed nerve. Methods. This experiment involved 48 rats in which radiolabeled ELPs (aggregating or soluble) were injected overlying the L5 dorsal root ganglion. Animals were killed at 6 different time points, and radioactivity associated with the injected segment, serum, and other tissues was evaluated. Results. The aggregating ELP demonstrated a 7-fold longer perineural half-life compared with the soluble ELP. This supports the hypothesis that the aggregating ELP forms a depot from which slow resolubilization and clearance provides sustained, local protein release. Furthermore, serum radioactivity reached a lower peak for the aggregating group, demonstrating slower absorption of the aggregating protein into the systemic circulation. Conclusion. These results suggest that ELP aggregation confer the benefit of perineural compartment longevity for bioactive therapeutics delivered fused with this carrier. This may sustain release of potent immunomodulator therapeutics to treat local neuroinflammation. Desirable features include delivery of high local doses and protection against systemic exposure and associated toxicity.}, Key = {Shamji08b} } @booklet{Boyd08, Author = {L. M. Boyd and W. J. Richardson and K. D. Allen and C. Flahiff and L. Jing and Y. Li and J. Chen and L. A. Setton}, Title = {Early-onset degeneration of the intervertebral disc and vertebral end plate in mice deficient in type IX collagen}, Journal = {Arthritis And Rheumatism}, Volume = {58}, Number = {1}, Pages = {164 -- 171}, Year = {2008}, Month = {January}, ISSN = {0004-3591}, Abstract = {Objective. Type IX collagen is an important component of the intervertebral disc extracellular matrix. Mutations in type IX collagen are associated with premature disc degeneration in mice and a predisposition to disc disorders in humans. The aim of this study was to assess the prevalence and timeline of intervertebral disc degeneration in mice homozygous for an inactivated Col9a1 gene. Methods. Intact spine segments were harvested from wild-type (WT) and type IX collagen-knockout (Col9a1(-/-)) mice at 3, 6, and 12 months of age. Sagittal spine sections were evaluated for evidence of histologic changes, by 2 blinded graders, using a semiquantitative grading method. Results. There was evidence of more degeneration of the disc and end plate in the spines of Col9a1(-/-) mice compared. with those of WT controls, at most time points. These findings were significant for the disc region at 3 and 6 months (P $<$ 0.01) and at 12 months (P $<$ 0.10) and for the end plate region only at 6 months (P $<$ 0.10). Degenerative changes in the disc consisted of cellular changes and mucous degeneration. Degeneration in the end plates was associated with more cell proliferation, cartilage disorganization, and new bone formation. Conclusion. A deletion mutation for type IX collagen is associated with connective tissue changes characteristic of musculoskeletal degeneration in bony and cartilaginous tissue regions. Some of the observed changes were similar to cartilage changes in osteoarthritis, while others were more similar to disc degenerative changes in humans. The finding of premature onset of intervertebral disc degeneration in this mouse model may be useful in studies of the pathology and treatment of human disc degeneration.}, Key = {Boyd08} } @booklet{Lim08, Author = {D. W. Lim and D. L. Nettles and L. A. Setton and A. Chilkoti}, Title = {In situ cross-linkinig of elastin-like polypeptide block copolymers for tissue repair}, Journal = {Biomacromolecules}, Volume = {9}, Number = {1}, Pages = {222 -- 230}, Year = {2008}, Month = {January}, ISSN = {1525-7797}, Abstract = {Rapid cross-linking of elastin-like polypeptides (ELPs) with hydroxymethylphosphines (HMPs) in aqueous solution is attractive for minimally invasive in vivo implantation of biomaterials and tissue engineering scaffolds. In order to examine the independent effect of the location and number of reactive sites on the chemical cross-linking kinetics of ELPs and the mechanical properties of the resulting hydrogels, we have designed ELP block copolymers comprised of cross-linkable, hydrophobic ELP blocks with periodic Lys residues (A block) and aliphatic, hydrophilic ELP blocks with no cross-linking sites (B block); three different block architectures, A, ABA, and BABA were synthesized in this study. All ELP block copolymers were rapidly cross-linked with HMPs within several minutes under physiological conditions. The inclusion of the un-cross-linked hydrophilic block, its length relative to the cross-linkable hydrophobic block, and the block copolymer architecture all had a significant effect on swelling ratios of the cross-linked hydrogels, their microstructure, and mechanical properties. Fibroblasts embedded in the ELP hydrogels survived the cross-linking process and remained viable for at least 3 days in vitro when the gels were formed from an equimolar ratio of HMPs and Lys residues of ELPs. DNA quantification of the embedded cells indicated that the cell viability within triblock ELP hydrogels was statistically greater than that in the monoblock gels at day 3. These results suggest that the mechanical properties of ELP hydrogels and the microenvironment that they present to cells can be tuned by the design of the block copolymer architecture.}, Key = {Lim08} } @booklet{Shamji07, Author = {M. F. Shamji and H. Betre and V. B. Kraus and J. Chen and A. Chilkoti and R. Pichika and K. Masuda and L. A. Setton}, Title = {Development and characterization of a fusion protein between thermally responsive elastin-like polypeptide and interleukin-1 receptor antagonist - Sustained release of a local antiinflammatory therapeutic}, Journal = {Arthritis And Rheumatism}, Volume = {56}, Number = {11}, Pages = {3650 -- 3661}, Year = {2007}, Month = {November}, ISSN = {0004-3591}, Abstract = {Objective. Interleukin-1 receptor antagonist (IL-1Ra) has been evaluated for the intraarticular treatment of osteoarthritis. Such administration of proteins may have limited utility because of their rapid clearance and short half-life in the joint. The fusion of a drug to elastin-like polypeptides (ELPs) promotes the formation of aggregating particles that form a "drug depot" at physiologic temperatures, a phenomenon intended to prolong the presence of the drug. The purpose of this study was to develop an injectable drug depot composed of IL-1Ra and ELP domains and to evaluate the properties and bioactivity of the recombinant ELP-IL-1Ra fusion protein. Methods. Fusion proteins between IL-1Ra and 2 distinct sequences and molecular weights of ELP were overexpressed in Escherichia coli. Environmental sensitivity was demonstrated by turbidity and dynamic light scattering as a function of temperature. IL-1Ra domain activity was evaluated by surface plasmon resonance, and in vitro antagonism of IL-1-mediated lymphocyte and thymocyte proliferation, as well as IL-1-induced tumor necrosis factor alpha (TNF alpha) expression and matrix metalloproteinase 3 (MMP-3) and ADAMTS-4 messenger RNA expression in human intervertebral disc fibrochondrocytes. IL-1Ra immunoreactivity was assessed before and after proteolytic degradation of the ELP partner. Results. Both fusion proteins underwent supramolecular aggregation at subphysiologic temperatures and slowly resolubilized at 37 degrees C. Interaction with IL-1 receptor was slower in association but equivalent in dissociation as compared with the commercial antagonist. Anti-IL-1 activity was demonstrated by inhibition of lymphocyte and thymocyte proliferation and by decreased TNFa expression and ADAMTS-4 and MMP-3 transcription by fibrochondrocytes. ELP domain proteolysis liberated a peptide of comparable size and immunoreactivity as the commercial IL-1Ra. This peptide was more bioactive against lymphocyte proliferation, nearly equivalent to the commercial antagonist. Conclusion. The ELP-IL-1Ra fusion protein proved to retain the characteristic ELP inverse phase-transitioning behavior as well as the bioactivity of the IL-1Ra domain. This technology represents a novel drug carrier designed to prolong the presence of bioactive peptides following intraarticular delivery.}, Key = {Shamji07} } @booklet{Cao07, Author = {L. Cao and F. Guilak and L. A. Setton}, Title = {Three-dimensional morphology of the pericellular matrix of intervertebral disc cells in the rat}, Journal = {Journal Of Anatomy}, Volume = {211}, Number = {4}, Pages = {444 -- 452}, Year = {2007}, Month = {October}, ISSN = {0021-8782}, Abstract = {Intervertebral disc cells are surrounded by a pericellular matrix that is biochemically and morphologically distinct from other extracellular matrix regions. Although the function of the pericellular matrix is not fully understood, prior studies of pericellular matrix-chondrocyte regions in articular cartilage (termed 'chondrons') suggest that the size, shape, and mechanical properties of the pericellular matrix significantly influence the micromechanical environment of the contained cells. A first step in understanding the role of the pericellular matrix in the intervertebral disc is to quantify the three-dimensional morphology and zonal variations of these regions across the disc. In this study, three-dimensional reconstructions and morphometric measurements of pericellular matrix-cell regions were obtained in situ using fluorescence confocal microscopy of en bloc sections of nucleus pulposus and anulus fibrosus of the rat disc immunolabeled for type VI collagen. The morphology of the pericellular matrix and cells varied significantly across regions, with distinct pericellular matrix aspect ratios (largest/smallest diameter) showing shapes that were generally large and rounded in the nucleus pulposus (average of 1.9), and ellipsoidal and discoidal in the inner (2.4) and outer anulus fibrosus (2.8). The average pericellular matrix volume per cell was found to be significantly larger in the nucleus (6424 mu m(3)) than that of inner (1903 mu m(3)) and outer (1433 mu m(3)) anulus. Pericellular matrix regions containing 1 or 2 cells were the dominant subgroup in the rat intervertebral disc at both 1 and 12 months of age. Multicellular pericellular matrix regions were present more often in the younger nucleus pulposus and outer anulus fibrosus. The orientation of the pericellular matrix regions further varied significantly across the disc, reflecting local collagen matrix architecture. These studies provide new information on the organization and shape of intervertebral disc cells and their surrounding pericellular matrix, which may provide new insights into the mechanisms that regulate cell-matrix interactions.}, Key = {Cao07} } @booklet{Roberts07, Author = {S. K. Roberts and A. Chilkoti and L. A. Setton}, Title = {Multifunctional thermally transitioning oligopeptides prepared by ring-opening metathesis polymerization}, Journal = {Biomacromolecules}, Volume = {8}, Number = {8}, Pages = {2618 -- 2621}, Year = {2007}, Month = {August}, ISSN = {1525-7797}, Key = {Roberts07} } @booklet{Gilchrist07, Author = {C. L. Gilchrist and J. Chen and W. J. Richardson and R. F. Loeser and L. A. Setton}, Title = {Functional integrin subunits regulating cell-matrix interactions in the intervertebral disc}, Journal = {Journal Of Orthopaedic Research}, Volume = {25}, Number = {6}, Pages = {829 -- 840}, Year = {2007}, Month = {June}, ISSN = {0736-0266}, Abstract = {Cellular interactions with the extracellular matrix are key factors regulating cell survival, differentiation, and response to environmental stimuli in cartilagenous tissues. Much is known about the extracellular matrix proteins in the intervertebral disc (IVD) and their variations with region, age, or degenerative state of the tissue. In contrast, little is known of the integrin cell surface receptors that directly bind to and interact with these matrix proteins in the IVD. In almost all tissues, these integrin-mediated cell-matrix interactions are important for transducing environmental cues arising from mechanical stimuli, matrix degradation fragments, and cytokines into intracellular signals. In this study, cells from the nucleus pulposus and anulus fibrosus regions of porcine IVDs were analyzed via flow cytometry to quantify integrin expression levels upon isolation and after monolayer culture. Assays of cell attachment to collagens, fibronectin, and laminin were performed after functional blocking of select integrin subunits to evaluate the role of specific integrins in cell attachment. In situ distribution and co-localization of integrins and laminin were also characterized. Results identify integrin receptors critical for IVD cell interactions with collagens (alpha 1 beta 1) and fibronectin (alpha 5 beta 1). Additionally, dramatic differences in cell-laminin interactions were observed between cells of the nucleus and anulus regions, including differences in alpha 6 integrin expression, cell adhesion to laminin, and in situ pericellular environments. These findings suggest laminin-cell interactions may be important and unique to the nucleus pulposus region of the IVD. The results of this study provide new information on functional cell-matrix interactions in tissues of the IVD. (C) 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.}, Key = {Gilchrist07} } @booklet{Lim07, Author = {D. W. Lim and D. L. Nettles and L. A. Setton and A. Chilkoti}, Title = {Rapid cross-linking of elastin-like polypeptides with (hydroxymethyl)phosphines in aqueous solution}, Journal = {Biomacromolecules}, Volume = {8}, Number = {5}, Pages = {1463 -- 1470}, Year = {2007}, Month = {May}, ISSN = {1525-7797}, Abstract = {In situ gelation of injectable polypeptide-based materials is attractive for minimally invasive in vivo implantation of biomaterials and tissue engineering scaffolds. We demonstrate that chemically cross-linked elastin-like polypeptide (ELP) hydrogels can be rapidly formed in aqueous solution by reacting lysine-containing ELPs with an organophosphorous cross-linker, beta-[tris(hydroxymethyl)phosphino]propionic acid (THPP) under physiological conditions. The mechanical properties of the cross-linked ELP hydrogels were largely modulated by the molar concentration of lysine residues in the ELP and the pH at which the cross-linking reaction was carried out. Fibroblasts embedded in ELP hydrogels survived the cross-linking process and were viable after in vitro culture for 3 days. DNA quantification of ELP hydrogels with encapsulated fibroblasts indicated that there was no significant difference in DNA content between day 0 and day 3 when ELP hydrogels were formed with an equimolar ratio of THPP and lysine residues of the ELPs. These results suggest that THPP cross-linking may be a biocompatible strategy for the in situ formation of cross-linked hydrogels.}, Key = {Lim07} } @article{070810438044, Author = {Gilchrist, Christopher L. and Witvoet-Braam, Sietske W. and Guilak, Farshid and Setton, Lori A.}, Title = {Measurement of intracellular strain on deformable substrates with texture correlation}, Journal = {Journal of Biomechanics}, Volume = {40}, Number = {4}, Pages = {786 - 794}, Year = {2007}, url = {http://dx.doi.org/10.1016/j.jbiomech.2006.03.013}, Keywords = {Biocommunications;Deformation;Metabolism;Microscopic examination;Stiffness;Strain measurement;}, Abstract = {Mechanical stimuli are important factors that regulate cell proliferation, survival, metabolism and motility in a variety of cell types. The relationship between mechanical deformation of the extracellular matrix and intracellular deformation of cellular sub-regions and organelles has not been fully elucidated, but may provide new insight into the mechanisms involved in transducing mechanical stimuli to biological responses. In this study, a novel fluorescence microscopy and image analysis method was applied to examine the hypothesis that mechanical strains are fully transferred from a planar, deformable substrate to cytoplasmic and intranuclear regions within attached cells. Intracellular strains were measured in cells derived from the anulus fibrosus of the intervertebral disc when attached to an elastic silicone membrane that was subjected to tensile stretch. Measurements indicated cytoplasmic strains were similar to those of the underlying substrate, with a strain transfer ratio (STR) of 0.79. In contrast, nuclear strains were much smaller than those of the substrate, with an STR of 0.17. These findings are consistent with previous studies indicating nuclear stiffness is significantly greater than cytoplasmic stiffness, as measured using other methods. This study provides a novel method for the study of cellular mechanics, including a new technique for measuring intranuclear deformations, with evidence of differential magnitudes and patterns of strain transferred from the substrate to cell cytoplasm and nucleus. © 2006 Elsevier Ltd. All rights reserved.}, Key = {070810438044} } @booklet{Choi07, Author = {J. B. Choi and I. Youn and L. Cao and H. A. Leddy and C. L. Gilchrist and L. A. Setton and F. Guilak}, Title = {Zonal changes in the three-dimensional morphology of the chondron under compression: The relationship among cellular, pericellular, and extracellular deformation in articular cartilage}, Journal = {Journal Of Biomechanics}, Volume = {40}, Number = {12}, Pages = {2596 -- 2603}, Year = {2007}, ISSN = {0021-9290}, Abstract = {The pericellular matrix (PCM) is a narrow region of tissue that completely surrounds chondrocytes in articular cartilage. Previous theoretical models of the "chondron" (the PCM with enclosed cells) suggest that the structure and properties of the PCM may significantly influence the mechanical environment of the chondrocyte. The objective of this study was to quantify changes in the three-dimensional (31) morphology of the chondron in situ at different magnitudes of compression applied to the cartilage extracellular matrix. Fluorescence immunolabeling for type-VI collagen was used to identify the boundaries of the cell and PCM, and confocal microscopy was used to form 3D images of chondrons from superficial, middle, and deep zone cartilage in explants compressed to 0\%, 10\%, 30\%, and 50\% surface-to-surface strain. Lagrangian tissue strain, determined locally using texture correlation, was highly inhomogeneous and revealed depth-dependent compressive stiffness and Poisson's ratio of the extracellular matrix. Compression significantly decreased cell and chondron height and volume, depending on the zone and magnitude of compression. In the superficial zone, cellular-level strains were always lower than tissue-level strains. In the middle and deep zones, however, tissue strains below 25\% were amplified at the cellular level, while tissue strains above 25\% were decreased at the cellular level. These findings are consistent with previous theoretical models of the chondron, suggesting that the PCM can serve as either a protective layer for the chondrocyte or a transducer that amplifies strain, such that cellular-level strains are more homogenous throughout the tissue depth despite large inhomogeneities in local ECM strains. (c) 2007 Elsevier Ltd. All rights reserved.}, Key = {Choi07} } @booklet{Gilchrist07a, Author = {C. L. Gilchrist and S. W. Witvoet-braam and F. Guilak and L. A. Setton}, Title = {Measurement of intracellular strain on deformable substrates with texture correlation}, Journal = {Journal Of Biomechanics}, Volume = {40}, Number = {4}, Pages = {786 -- 794}, Year = {2007}, ISSN = {0021-9290}, Abstract = {Mechanical stimuli are important factors that regulate cell proliferation, survival, metabolism and motility in a variety of cell types. The relationship between mechanical deformation of the extracellular matrix and intracellular deformation of cellular sub-regions and organelles has not been fully elucidated, but may provide new insight into the mechanisms involved in transducing mechanical stimuli to biological responses. In this study, a novel fluorescence microscopy and image analysis method was applied to examine the hypothesis that mechanical strains are fully transferred from a planar, deformable substrate to cytoplasmic and intranuclear regions within attached cells. Intracellular strains were measured in cells derived from the anulus fibrosus of the intervertebral disc when attached to an elastic silicone membrane that was subjected to tensile stretch. Measurements indicated cytoplasmic strains were similar to those of the underlying substrate, with a strain transfer ratio (STR) of 0.79. In contrast, nuclear strains were much smaller than those of the substrate, with an STR of 0.17. These findings are consistent with previous studies indicating nuclear stiffness is significantly greater than cytoplasmic stiffness, as measured using other methods. This study provides a novel method for the study of cellular mechanics, including a new technique for measuring intranuclear deformations, with evidence of differential magnitudes and patterns of strain transferred from the substrate to cell cytoplasm and nucleus. (c) 2006 Elsevier Ltd. All rights reserved.}, Key = {Gilchrist07a} } @booklet{Betre06, Author = {H. Betre and W. Liu and M. R. Zalutsky and A. Chilkoti and V. B. Kraus and L. A. Setton}, Title = {A thermally responsive biopolymer for intra-articular drug delivery}, Journal = {Journal Of Controlled Release}, Volume = {115}, Number = {2}, Pages = {175 -- 182}, Year = {2006}, Month = {October}, ISSN = {0168-3659}, Abstract = {Intra-articular drug delivery is the preferred standard for targeting pharmacologic treatment directly to joints to reduce undesirable side effects associated with systemic drug delivery. In this study, a biologically based drug delivery vehicle was designed for intra-articular drug delivery using elastin-like polypeptides (ELPs), a biopolymer composed of repeating pentapeptides that undergo a phase transition to form aggregates above their transition temperature. The ELP drug delivery vehicle was designed to aggregate upon intra-articular injection at 37 degrees C, and form a drug 'depot' that could slowly disaggregate and be cleared from the joint space over time. We evaluated the in vivo biodistribution and joint half-life of radiolabeled ELPs, with and without the ability to aggregate, at physiological temperatures encountered after intra-articular injection in a rat knee. Biodistribution studies revealed that the aggregating ELP had a 25-fold longer half-life in the injected joint than a similar molecular weight protein that remained soluble and did not aggregate. These results suggest that the intra-articular joint delivery of ELP-based fusion proteins may be a viable strategy for the prolonged release of disease-modifying protein drugs for ostcoarthritis and other arthritides. (c) 2006 Elsevier B.V. All rights reserved.}, Key = {Betre06} } @booklet{Cao06, Author = {L. Cao and I. Youn and F. Guilak and L. A. Setton}, Title = {Compressive properties of mouse articular cartilage determined in a novel micro-indentation test method and biphasic finite element model}, Journal = {Journal Of Biomechanical Engineering-transactions Of The Asme}, Volume = {128}, Number = {5}, Pages = {766 -- 771}, Year = {2006}, Month = {October}, ISSN = {0148-0731}, Abstract = {The mechanical Properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with osteoarthritis. Interest in small animal and mouse models of osteoarthritis has increased as studies reveal the importance of genetic background in determining predisposition to osteoarthritis. While indentation testing provides a method of determining cartilage mechanical properties in situ, it has been of limited value in studying mouse joints due to the relatively small size of the joint and thickness of the cartilage layer In this study, we developed a micro-indentation testing system to determine the compressive and biphasic mechanical properties of cartilage in the small joints of the mouse. A nonlinear optimization program employing a genetic algorithm for parameter estimation, combined with a biphasic finite element model of the micro-indentation test, was developed to obtain the biphasic, compressive material properties of articular cartilage. The creep response and material properties of lateral tibial plateau cartilage were obtained for wild-type mouse knee joints, by the micro-indentation testing and optimization algorithm. The newly developed genetic algorithm was found to be efficient and accurate when used with the finite element simulations for nonlinear optimization to the experimental creep data. The biphasic mechanical properties of mouse cartilage in compression (average values: Young's modulus, 2.0 MPa; Poisson's ratio, 0.20; and hydraulic permeability, 1.1 X 10(-16) m(4) /N-s) were found to be of similar orders of magnitude as previous findings for other animal cartilages, including human, bovine, rat, and rabbit and demonstrate the utility of the new test methods. This study provides the first available data for biphasic compressive properties in mouse cartilage and suggests a promising method for detecting altered cartilage mechanics in small animal models of osteoarthritis.}, Key = {Cao06} } @booklet{Youn06, Author = {I. Youn and J. B. Choi and L. Cao and L. A. Setton and F. Guilak}, Title = {Zonal variations in the three-dimensional morphology of the chondron measured in situ using confocal microscopy}, Journal = {Osteoarthritis And Cartilage}, Volume = {14}, Number = {9}, Pages = {889 -- 897}, Year = {2006}, Month = {September}, ISSN = {1063-4584}, Abstract = {Objective: Chondrocytes in articular cartilage are surrounded by a narrow pericellular matrix (PCM), which together with the enclosed cell(s) are termed the "chondron". Although the precise function of this tissue region is unknown, previous studies provide indirect evidence that the PCM plays an important role in governing the local mechanical environment of chondrocytes. In particular, theoretical models of the chondron under mechanical loading suggest that the shape, size, and biomechanical properties of the PCM significantly influence the stress-strain and fluid flow environment of the cell. The goal of this study was to quantify the three-dimensional morphology of chondron in situ using en bloc immunolabeling of type VI collagen coupled with fluorescence confocal microscopy. Methods: Three-dimensional reconstructions of intact, fluorescently labeled chondrons were made from stacks of confocal images recorded in situ from the superficial, middle, and deep zones of porcine articular cartilage of the medial femoral condyle. Results: Significant variations in the shape, size, and orientation of chondrocytes and chondrons were observed with depth from the tissue surface, revealing flattened discoidal chondrons in the superficial zone, rounded chondrons in the middle zone, and elongated, multicellular chondrons in the deep zone. Conclusions: The shape and orientation of the chondron appear to reflect the local collagen architecture of the interterritorial matrix, which varies significantly with depth. Quantitative measurements of morphology of the chondron and its variation with site, disease, or aging may provide new insights into the influence of this structure on physiology and the pathology of articular cartilage. (C) 2006 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.}, Key = {Youn06} } @booklet{Hu06, Author = {K. Hu and L. Xu and L. Cao and C. M. Flahiff and J. Brussiau and K. Ho and L. A. Setton and I. Youn and F. Guilak and B. R. Olsen and Y. Li}, Title = {Pathogenesis of osteoarthritis-like changes in the joints of mice deficient in type IX collagen}, Journal = {Arthritis And Rheumatism}, Volume = {54}, Number = {9}, Pages = {2891 -- 2900}, Year = {2006}, Month = {September}, ISSN = {0004-3591}, Abstract = {Objective. To examine the pathogenetic mechanisms of osteoarthritis (OA)-like changes in Col9a1(-/-) mice, which are deficient in type IX collagen. Methods. Knee joints and temporomandibular joints (TMJs) from Col9a1(-/-) mice and their wild-type (Col9a1(+/+)) littermates were examined by light microscopy. Immunohistochemical staining was performed to examine the expression of matrix metalloproteinase 3 (MMP-3) and MMP-13, degraded type II collagen, and the discoidin domain receptor 2 (DDR-2) in knee joints. Cartilage mechanics were also evaluated for compressive properties by microindentation testing of the tibial plateau and for tensile properties by osmotic loading of the femoral condyle. Results. Histologic analysis showed age-dependent OA-like changes in the knee and TMJs of Col9a1(-/-) mice starting at the age of 3 months. At the age of 6 months, enhanced proteoglycan degradation was observed in the articular cartilage of the knee and TMJs of the mutant mice. The expression of MMP-13 and DDR-2 protein and the amount of degraded type II collagen were higher in the knee joints of Col9a1(-/-) mice than in their wild-type littermates at the age of 6 months. Changes in cartilage mechanics were observed in the femoral and tibial plateaus of Col9a1(-/-) mice at 6 months, including a decrease in the compressive modulus and uniaxial modulus. At 3 and 6 months of age, tibial cartilage in Col9a1(-/-) mice was found to be more permeable to fluid flow, with an associated compromise in the fluid pressurization mechanism of load support. All of these changes occurred only at medial sites. Conclusion. Lack of type IX collagen in Col9a1(-/-) mice results in age-dependent OA-like changes in the knee joints and TMJs.}, Key = {Hu06} } @booklet{Chen06, Author = {J. Chen and W. Yan and L. A. Setton}, Title = {Molecular phenotypes of notochordal cells purified from immature nucleus pulposus}, Journal = {European Spine Journal}, Volume = {15}, Pages = {S303 -- S311}, Year = {2006}, Month = {August}, ISSN = {0940-6719}, Abstract = {The immature nucleus pulposus (NP) is populated by cells of notochordal-origin that are larger and contain an extensive cytoskeletal network and numerous vacuoles. The disappearance of these cells with age is believed important in regulating metabolic shifts that may contribute to age-related disc degeneration. The precise biological function of these notochordal cells in the immature NP remains unclear, however, because of challenges in studying the mixed cell population in the NP. In this study, notochordal-like cells were purified from immature NP cells using a new fluorescence-activated cell sorting (FACS) protocol with auto-fluorescence and size analysis. The unique molecular phenotypes of sorted notochordal-like cells were characterized by the mRNA expression pattern for key matrix proteins and modulators, and by the expression of cell matrix receptor integrin subunits. An FACS analysis showed that the immature NP contained a majority of cells that were larger than anulus fibrosus (AF) cells and with fluorescence higher than AF cells. In comparison with the small NP cells separated by the FACS protocol, sorted notochordal-like cells expressed lower mRNA levels of type I collagen, biglycan, TIMP1, HSP70 and c-fos, and did not express detectable mRNA levels of decorin, lumican, multiple MMPs or IL-1 beta via real-time quantitative RT-PCR. A greater number of these notochordal-like cells also expressed the higher levels of alpha 6, alpha 1 and beta 1 integrin subunits as compared to small NP cells. Together, our results point towards a unique molecular phenotype for these notochordal-like cells of NP, characterized by the absence of gene expression for specific small proteoglycans and higher protein expression of integrin subunits that regulate interactions with collagens and laminin. Future studies will be important for revealing if this unique molecular profile is coordinated with functional differences in pericellular matrix regions and/or tritegrin-mediated cell-matrix interactions for these notochordal-like cells within the NP.}, Key = {Chen06} } @booklet{Upton06a, Author = {M. L. Upton and J. Chen and L. A. Setton}, Title = {Region-specific constitutive gene expression in the adult porcine meniscus}, Journal = {Journal Of Orthopaedic Research}, Volume = {24}, Number = {7}, Pages = {1562 -- 1570}, Year = {2006}, Month = {July}, ISSN = {0736-0266}, Abstract = {The knee meniscus exhibits extensive spatial variations in native healing capacity, biochemical composition, and cell morphology that suggest the existence of distinct phenotypes for meniscus cells. Constitutive gene expression levels of appropriate extracellular matrix proteins may serve as useful molecular markers of cellular phenotypes; however, relatively little is known of variations in the gene expression for meniscus cells of different regions of the tissue. The objective of the present study was to evaluate constitutive differences between radial inner and outer regions in gene expression for extracellular matrix proteins relevant to the meniscus. A secondary objective was to determine if these region-specific differences in gene expression are maintained after periods of monolayer culture. The innermost regions of the meniscus were found to constitutively express higher mRNA levels for proteins highly expressed in articular cartilage, including aggrecan, type 11 collagen, and NOS2. In contrast, the outer meniscus was found to contain higher gene expression for proteins associated with fibrous tissues including type I collagen, and the proteases MMP2 and MMP3. Isolated inner and outer meniscus cells maintained these region-specific gene expression patterns for collagens and proteoglycans during short-term monolayer culture. The results provide new information that suggests the utility of constitutive gene expression levels as molecular markers to distinguish tissue and cells of the inner and outer meniscus. (c) 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.}, Key = {Upton06a} } @booklet{Upton06b, Author = {M. L. Upton and F. Guilak and T. A. Laursen and L. A. Setton}, Title = {Finite element modeling predictions of region-specific cell-matrix mechanics in the meniscus}, Journal = {Biomechanics And Modeling In Mechanobiology}, Volume = {5}, Number = {2-3}, Pages = {140 -- 149}, Year = {2006}, Month = {June}, ISSN = {1617-7959}, Abstract = {The knee meniscus exhibits significant spatial variations in biochemical composition and cell morphology that reflect distinct phenotypes of cells located in the radial inner and outer regions. Associated with these cell phenotypes is a spatially heterogeneous microstructure and mechanical environment with the innermost regions experiencing higher fluid pressures and lower tensile strains than the outer regions. It is presently unknown, however, how meniscus tissue mechanics correlate with the local micromechanical environment of cells. In this study, theoretical models were developed to study mechanics of inner and outer meniscus cells with varying geometries. The results for an applied biaxial strain predict significant regional differences in the cellular mechanical environment with evidence of tensile strains along the collagen fiber direction of similar to 0.07 for the rounded inner cells, as compared to levels of 0.02-0.04 for the elongated outer meniscus cells. The results demonstrate an important mechanical role of extracellular matrix anisotropy and cell morphology in regulating the region-specific micromechanics of meniscus cells, that may further play a role in modulating cellular responses to mechanical stimuli.}, Key = {Upton06b} } @booklet{Haider06, Author = {M. A. Haider and R. C. Schugart and L. A. Setton and F. Guilak}, Title = {A mechano-chemical model for the passive swelling response of an isolated chondron under osmotic loading}, Journal = {Biomechanics And Modeling In Mechanobiology}, Volume = {5}, Number = {2-3}, Pages = {160 -- 171}, Year = {2006}, Month = {June}, ISSN = {1617-7959}, Abstract = {The chondron is a distinct structure in articular cartilage that consists of the chondrocyte and its pericellular matrix (PCM), a narrow tissue region surrounding the cell that is distinguished by type VI collagen and a high glycosaminoglycan concentration relative to the extracellular matrix. We present a theoretical mechano-chemical model for the passive volumetric response of an isolated chondron under osmotic loading in a simple salt solution at equilibrium. The chondrocyte is modeled as an ideal osmometer and the PCM model is formulated using triphasic mixture theory. A mechano-chemical chondron model is obtained assuming that the chondron boundary is permeable to both water and ions, while the chondrocyte membrane is selectively permeable to only water. For the case of a neo-Hookean PCM constitutive law, the model is used to conduct a parametric analysis of cell and chondron deformation under hyper- and hypo-osmotic loading. In combination with osmotic loading experiments on isolated chondrons, model predictions will aid in determination of pericellular fixed charge density and its relative contribution to PCM mechanical properties.}, Key = {Haider06} } @booklet{Andersson06, Author = {G. B. J. Andersson and H. S. An and T. R. Oegema and L. A. Setton}, Title = {Intervertebral disc degeneration - Summary of an AAOS/NIH/ORS Workshop, September 2005}, Journal = {Journal Of Bone And Joint Surgery-american Volume}, Volume = {88A}, Number = {4}, Pages = {895 -- 899}, Year = {2006}, Month = {April}, ISSN = {0021-9355}, Key = {Andersson06} } @booklet{Ong06, Author = {S. R. Ong and K. A. Trabbic-carlson and D. L. Nettles and D. W. Lim and A. Chilkoti and L. A. Setton}, Title = {Epitope tagging for tracking elastin-like polypeptides}, Journal = {Biomaterials}, Volume = {27}, Number = {9}, Pages = {1930 -- 1935}, Year = {2006}, Month = {March}, ISSN = {0142-9612}, Abstract = {Elastin-like polypeptides (ELPs) are a class of biocompatible, non-immunogenic and crosslinkable biomaterials that offer promise for use as an injectable scaffold for cartilage repair. In this study, an oligohistidine (His(6)) epitope tag was incorporated at the N-terminus of an ELP using recombinant DNA techniques to permit tracking without compromising on material biocompatibility. His(6)-tagged ELPs were successfully detected by Western blot analysis and quantified by ELISAs following digestion with trypsin. The mass of His(6) tagged ELP fragments freed from a crosslinked ELP hydrogel after digestion with trypsin correlated highly with hydrogel weight loss, providing evidence of the tag's capability to enable tracking of enzymatic degradation of the ELP hydrogel. The His(6) tag also facilitated recognition of crosslinked ELPs from background staining of articular cartilage. These results suggest that the His(6) epitope tag has the potential to track ELP scaffold loss independently of newly formed tissue mass for evaluating matrix remodeling in vivo. (C) 2005 Elsevier Ltd. All rights reserved.}, Key = {Ong06} } @booklet{Hyun06, Author = {J. H. Hyun and J. Chen and L. A. Setton and A. Chilkoti}, Title = {Patterning cells in highly deformable micro structures: Effect of plastic deformation of substrate on cellular phenotype and gene expression}, Journal = {Biomaterials}, Volume = {27}, Number = {8}, Pages = {1444 -- 1451}, Year = {2006}, Month = {March}, ISSN = {0142-9612}, Abstract = {We describe the fabrication of deformable microstructures by low-pressure-soft-microembossing (mu SEmb) that provides in vitro experimental "test-beds" to investigate the interplay of mechanical and chemical stimuli on cell behavior in a highly controlled environment. Soft microembossing exploits the softness and plasticity of parafilm to fabricate microstructures by pressing a silicon master or an elastomeric poly(dimethylsiloxane) stamp into the parafilm. We demonstrate that a protein-resistant comb polymer can be printed into the raised features of the embossed micro structures, which imparts protein, and hence cell resistance to those regions of the microstructures. These two features of our fabrication methodology-microembossing followed by spatially selective transfer of a nonfouling polymer-forms the core of our strategy to pattern cells within the parafilm microstructures, such that the cells are confined within bottoms of the microstructures. Cell culture experiments demonstrated the preferential cell attachment of NIH 3T3 fibroblasts to the fibronectin (FN) micropatterns by immunofluorescence microscopy. The actin cytoskeleton realigned along the axis of applied mechanical stress, and stretched cells showed altered gene expression of cytoskeletal and matrix proteins in response to mechanical deformation. The use of parafilm as a substrate and mu SEmb as a fabrication method provides a simple and widely accessible methodology to investigate cellular behavior tinder well-defined conditions of plastic deformation and surface ligand density. (c) 2005 Elsevier Ltd. All rights reserved.}, Key = {Hyun06} } @booklet{Sontjens06, Author = {S. H. M. Sontjens and D. L. Nettles and M. A. Carnahan and L. A. Setton and M. W. Grinstaff}, Title = {Biodendrimer-based hydrogel scaffolds for cartilage tissue repair}, Journal = {Biomacromolecules}, Volume = {7}, Number = {1}, Pages = {310 -- 316}, Year = {2006}, Month = {January}, ISSN = {1525-7797}, Abstract = {Photo-crosslinkable dendritic macromolecules are attractive materials for the preparation of cartilage tissue engineering scaffolds that may be optimized for in situ formation of hydrated, mechanically stable, and wellintegrated hydrogel scaffolds supporting chondrocytes and chondrogenesis. We designed and synthesized a novel hydrogel scaffold for cartilage repair, based on a multivalent and water-soluble tri-block copolymer consisting of a poly(ethylene glycol) core and methacrylated poly(glycerol succinic acid) dendrimer terminal blocks. The terminal methacrylates allow mild and biocompatible photo-crosslinking with a visible light, facilitating in vivo filling of irregularly shaped defects with the dendrimer-based scaffold. The multivalent dendrimer constituents allow high crosslink densities that inhibit swelling after crosslinking while simultaneously introducing biodegradation sites. The mechanical properties and water content of the hydrogel can easily be tuned by changing the biodendrimer concentration. In vitro chondrocyte encapsulation studies demonstrate significant synthesis of neocartilaginous material, containing proteoglycans and type 11 collagen.}, Key = {Sontjens06} } @article{9108356, Author = {Li Cao and Youn, I. and Guilak, F. and Setton, L.A.}, Title = {Compressive properties of mouse articular cartilage determined in a novel micro-indentation test method and biphasic finite element model}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {128}, Number = {5}, Pages = {766 - 71}, Year = {2006}, url = {http://dx.doi.org/10.1115/1.2246237}, Keywords = {biological tissues;biomechanics;creep;diseases;finite element analysis;genetic algorithms;indentation;parameter estimation;permeability;physiological models;Poisson ratio;Young's modulus;}, Abstract = {The mechanical properties of articular cartilage serve as important measures of tissue function or degeneration, and are known to change significantly with osteoarthritis. Interest in small animal and mouse models of osteoarthritis has increased as studies reveal the importance of genetic background in determining predisposition to osteoarthritis. While indentation testing provides a method of determining cartilage mechanical properties in situ, it has been of limited value in studying mouse joints due to the relatively small size of the joint and thickness of the cartilage layer. In this study, we developed a micro-indentation testing system to determine the compressive and biphasic mechanical properties of cartilage in the small joints of the mouse. A nonlinear optimization program employing a genetic algorithm for parameter estimation, combined with a biphasic finite element model of the micro-indentation test, was developed to obtain the biphasic, compressive material properties of articular cartilage. The creep response and material properties of lateral tibial plateau cartilage were obtained for wild-type mouse knee joints, by the micro-indentation testing and optimization algorithm. The newly developed genetic algorithm was found to be efficient and accurate when used with the finite element simulations for nonlinear optimization to the experimental creep data. The biphasic mechanical properties of mouse cartilage in compression (average values: Young's modulus, 2.0 MPa; Poisson's ratio, 0.20; and hydraulic permeability, 1.1×10<sup>-16</sup> m<sup>4</sup>/N-s) were found to be of similar orders of magnitude as previous findings for other animal cartilages, including human, bovine, rat, and rabbit and demonstrate the utility of the new test methods. This study provides the first available data for biphasic compressive properties in mouse cartilage and suggests a promising method for detecting altered cartilage mechanics in small animal models of osteoarthritis}, Key = {9108356} } @article{06059678393, Author = {Sontjens, Serge H.M. and Nettles, Dana L. and Carnahan, Michael A. and Setton, Lori A. and Grinstaff, Mark W.}, Title = {Biodendrimer-based hydrogel scaffolds for cartilage tissue repair}, Journal = {Biomacromolecules}, Volume = {7}, Number = {1}, Pages = {310 - 316}, Year = {2006}, url = {http://dx.doi.org/10.1021/bm050663e}, Keywords = {Dendrimers;Biological materials;Macromolecules;Tissue;Synthesis (chemical);Block copolymers;Acrylic monomers;Biocompatibility;Crosslinking;Biodegradation;Mechanical properties;Encapsulation;}, Abstract = {Photo-crosslinkable dendritic macromolecules are attractive materials for the preparation of cartilage tissue engineering scaffolds that may be optimized for in situ formation of hydrated, mechanically stable, and well-integrated hydrogel scaffolds supporting chondrocytes and chondrogenesis. We designed and synthesized a novel hydrogel scaffold for cartilage repair, based on a multivalent and water-soluble tri-block copolymer consisting of a poly(ethylene glycol) core and methacrylated poly(glycerol succinic acid) dendrimer terminal blocks. The terminal methacrylates allow mild and biocompatible photo-crosslinking with a visible light, facilitating in vivo filling of irregularly shaped defects with the dendrimer-based scaffold. The multivalent dendrimer constituents allow high crosslink densities that inhibit swelling after crosslinking while simultaneously introducing biodegradation sites. The mechanical properties and water content of the hydrogel can easily be tuned by changing the biodendrimer concentration. In vitro chondrocyte encapsulation studies demonstrate significant synthesis of neocartilaginous material, containing proteoglycans and type II collagen. © 2006 American Chemical Society.}, Key = {06059678393} } @article{064210174605, Author = {Betre, Helawe and Liu, Wenge and Zalutsky, Michael R. and Chilkoti, Ashutosh and Kraus, Virginia B. and Setton, Lori A.}, Title = {A thermally responsive biopolymer for intra-articular drug delivery}, Journal = {Journal of Controlled Release}, Volume = {115}, Number = {2}, Pages = {175 - 182}, Year = {2006}, url = {http://dx.doi.org/10.1016/j.jconrel.2006.07.022}, Keywords = {Controlled drug delivery;Pharmacokinetics;Polypeptides;Phase transitions;Joints (anatomy);Diseases;}, Abstract = {Intra-articular drug delivery is the preferred standard for targeting pharmacologic treatment directly to joints to reduce undesirable side effects associated with systemic drug delivery. In this study, a biologically based drug delivery vehicle was designed for intra-articular drug delivery using elastin-like polypeptides (ELPs), a biopolymer composed of repeating pentapeptides that undergo a phase transition to form aggregates above their transition temperature. The ELP drug delivery vehicle was designed to aggregate upon intra-articular injection at 37 °C, and form a drug 'depot' that could slowly disaggregate and be cleared from the joint space over time. We evaluated the in vivo biodistribution and joint half-life of radiolabeled ELPs, with and without the ability to aggregate, at physiological temperatures encountered after intra-articular injection in a rat knee. Biodistribution studies revealed that the aggregating ELP had a 25-fold longer half-life in the injected joint than a similar molecular weight protein that remained soluble and did not aggregate. These results suggest that the intra-articular joint delivery of ELP-based fusion proteins may be a viable strategy for the prolonged release of disease-modifying protein drugs for osteoarthritis and other arthritides. © 2006 Elsevier B.V. All rights reserved.}, Key = {064210174605} } @booklet{Setton06, Author = {L. A. Setton and J. Chen}, Title = {Mechanobiology of the intervertebral disc and relevance to disc degeneration}, Journal = {Journal Of Bone And Joint Surgery-american Volume}, Volume = {88A}, Pages = {52 -- 57}, Year = {2006}, ISSN = {0021-9355}, Abstract = {Mechanical loading of the intervertebral disc may contribute to disc degeneration by initiating degeneration or by regulating cell-mediated remodeling events that occur in response to the mechanical stimuli of daily activity. This article is a review of the current knowledge of the role of mechanical stimuli in regulating intervertebral disc cellular responses to loading and the cellular changes that occur with degeneration. Intervertebral disc cells exhibit diverse biologic responses to mechanical stimuli, depending on the loading type, magnitude, duration, and anatomic zone of cell origin. The innermost cells respond to low-to-moderate magnitudes of static compression, osmotic pressure, or hydrostatic pressure with increases in anabolic cell responses. Higher magnitudes of loading may give rise to catabolic responses marked by elevated protease gene or protein expression or activity. The key regulators of these mechanobiologic responses for intervertebral disc cells will be the micromechanical stimuli experienced at the cellular level, which are predicted to differ from that measured for the extracellular matrix. Large hydrostatic pressures, but little volume change, are predicted to occur for cells of the nucleus pulposus during compression, while the highly oriented cells of the anulus fibrosus may experience deformations in tension or compression during matrix deformations. In general, the pattern of biologic response to applied loads suggests that the cells of the nucleus pulposus and inner portion of the anulus fibrosus experience comparable micromechanical stimuli in situ and may respond more similarly than cells of the outer portion of the anulus fibrosus. Changes in these features with degeneration are critically understudied, particularly degeneration-associated changes in cell-level mechanical stimuli and the associated mechanobiology. Little is known of the mechanisms that regulate cellular responses to intervertebral mechanobiology, nor is much known with regard to the precise mechanical stimuli experienced by cells during loading. Mechanical factors appear to regulate responses of the intervertebral disc cells through mechanisms involving intracellular Ca2+ transients and cytoskeletal remodeling that may regulate downstream effects such as gene expression and posttranslational biosynthesis. Future studies should address the broader biologic responses to mechanical stimuli in intervertebral disc mechanobiology, the involved signaling mechanisms, and the apparently important interactions among mechanical factors, genetic factors, cytokines, and inflammatory mediators that may be critical in the regulation of intervertebral disc degeneration.}, Key = {Setton06} } @booklet{Guilak06, Author = {F. Guilak and L. G. Alexopoulos and M. L. Upton and I. Youn and J. B. Choi and L. Cao and L. A. Setton and M. A. Haider}, Title = {The pericellular matrix as a transducer of biomechanical and biochemical signals in articular cartilage}, Journal = {Skeletal Development And Remodeling In Health, Disease, And Aging}, Volume = {1068}, Series = {ANNALS OF THE NEW YORK ACADEMY OF SCIENCES}, Pages = {498 -- 512}, Year = {2006}, ISSN = {0077-8923}, Abstract = {The pericellular matrix (PCM) is a narrow tissue region surrounding chondrocytes in articular cartilage, which together with the enclosed cell(s) has been termed the "chondron." While the function of this region is not fully understood, it is hypothesized to have important biological and biomechanical functions. In this article, we review a number of studies that have investigated the structure, composition, mechanical properties, and biomechanical role of the chondrocyte PCM. This region has been shown to be rich in proteoglycans (e.g., aggrecan, hyaluronan, and decorin), collagen (types II, VI, and IX), and fibronectin, but is defined primarily by the presence of type VI collagen as compared to the extracellular matrix (ECM). Direct measures of PCM properties via micropipette aspiration of isolated chondrons have shown that the PCM has distinct mechanical properties as compared to the cell or ECM. A number of theoretical and experimental studies suggest that the PCM plays an important role in regulating the microenvironment of the chondrocyte. Parametric studies of cell-matrix interactions suggest that the presence of the PCM significantly affects the micromechanical environment of the chondrocyte in a zone-dependent manner. These findings provide support for a potential biomechanical function of the chondrocyte PCM, and furthermore, suggest that changes in the PCM and ECM properties that occur with osteoarthritis may significantly alter the stress-strain and fluid environments of the chondrocytes. An improved understanding of the structure and function of the PCM may provide new insights into the mechanisms that regulate chondrocyte physiology in health and disease.}, Key = {Guilak06} } @article{9160417, Author = {Upton, M.L. and Guilak, F. and Laursen, T.A. and Setton, L.A.}, Title = {Finite element modeling predictions of region-specific cell-matrix mechanics in the meniscus}, Journal = {Biomech. Modeling Mechanobiol. (Germany)}, Volume = {5}, Number = {2-3}, Pages = {140 - 9}, Year = {2006}, url = {http://dx.doi.org/10.1007/s10237-006-0031-4}, Keywords = {biochemistry;biological tissues;biomechanics;cellular biophysics;finite element analysis;molecular biophysics;physiological models;proteins;}, Abstract = {The knee meniscus exhibits significant spatial variations in biochemical composition and cell morphology that reflect distinct phenotypes of cells located in the radial inner and outer regions. Associated with these cell phenotypes is a spatially heterogeneous microstructure and mechanical environment with the innermost regions experiencing higher fluid pressures and lower tensile strains than the outer regions. It is presently unknown, however, how meniscus tissue mechanics correlate with the local micromechanical environment of cells. In this study, theoretical models were developed to study mechanics of inner and outer meniscus cells with varying geometries. The results for an applied biaxial strain predict significant regional differences in the cellular mechanical environment with evidence of tensile strains along the collagen fiber direction of ~0.07 for the rounded inner cells, as compared to levels of 0.02-0.04 for the elongated outer meniscus cells. The results demonstrate an important mechanical role of extracellular matrix anisotropy and cell morphology in regulating the region-specific micromechanics of meniscus cells, that may further play a role in modulating cellular responses to mechanical stimuli}, Key = {9160417} } @article{9150369, Author = {Haider, M.A. and Schugart, R.C. and Setton, L.A. and Guilak, F.}, Title = {A mechano-chemical model for the passive swelling response of an isolated chondron under osmotic loading}, Journal = {Biomech. Modeling Mechanobiol. (Germany)}, Volume = {5}, Number = {2-3}, Pages = {160 - 71}, Year = {2006}, url = {http://dx.doi.org/10.1007/s10237-006-0026-1}, Keywords = {biochemistry;biodiffusion;bioelectric phenomena;biomechanics;biomembranes;biorheology;deformation;molecular biophysics;osmosis;physiological models;proteins;}, Abstract = {The chondron is a distinct structure in articular cartilage that consists of the chondrocyte and its pericellular matrix (PCM), a narrow tissue region surrounding the cell that is distinguished by type VI collagen and a high glycosaminoglycan concentration relative to the extracellular matrix. We present a theoretical mechano-chemical model for the passive volumetric response of an isolated chondron under osmotic loading in a simple salt solution at equilibrium. The chondrocyte is modeled as an ideal osmometer and the PCM model is formulated using triphasic mixture theory. A mechano-chemical chondron model is obtained assuming that the chondron boundary is permeable to both water and ions, while the chondrocyte membrane is selectively permeable to only water. For the case of a neo-Hookean PCM constitutive law, the model is used to conduct a parametric analysis of cell and chondron deformation under hyper- and hypo-osmotic loading. In combination with osmotic loading experiments on isolated chondrons, model predictions will aid in determination of pericellular fixed charge density and its relative contribution to PCM mechanical properties}, Key = {9150369} } @article{8837010, Author = {Jinho Hyun and Jun Chen and Setton, L.A. and Chilkoti, A.}, Title = {Patterning cells in highly deformable microstructures: Effect of plastic deformation of substrate on cellular phenotype and gene expression}, Journal = {Biomaterials (UK)}, Volume = {27}, Number = {8}, Pages = {1444 - 51}, Year = {2006}, url = {http://dx.doi.org/10.1016/j.biomaterials.2005.08.018}, Keywords = {biomechanics;cellular biophysics;deformation;elastomers;embossing;plasticity;proteins;silicon;tissue engineering;}, Abstract = {We describe the fabrication of deformable microstructures by low-pressure-soft-microembossing (μSEmb) that provides in vitro experimental "test-beds" to investigate the interplay of mechanical and chemical stimuli on cell behavior in a highly controlled environment. Soft microembossing exploits the softness and plasticity of parafilm to fabricate microstructures by pressing a silicon master or an elastomeric poly(dimethylsiloxane) stamp into the parafilm. We demonstrate that a protein-resistant comb polymer can be printed into the raised features of the embossed microstructures, which imparts protein, and hence cell resistance to those regions of the microstructures. These two features of our fabrication methodology-microembossing followed by spatially selective transfer of a nonfouling polymer-forms the core of our strategy to pattern cells within the parafilm microstructures, such that the cells are confined within bottoms of the microstructures. Cell culture experiments demonstrated the preferential cell attachment of NIH 3T3 fibroblasts to the fibronectin (FN) micropatterns by immunofluorescence microscopy. The actin cytoskeleton realigned along the axis of applied mechanical stress, and stretched cells showed altered gene expression of cytoskeletal and matrix proteins in response to mechanical deformation. The use of parafilm as a substrate and μSEmb as a fabrication method provides a simple and widely accessible methodology to investigate cellular behavior under well-defined conditions of plastic deformation and surface ligand density. [All rights reserved Elsevier]}, Key = {8837010} } @article{8827248, Author = {Setton, L.A. and Ong, S.R. and Trabbic-Carlson, K.A. and Nettles, D.L. and Lim, D.W. and Chilkoti, A.}, Title = {Epitope tagging for tracking elastin-like polypeptides}, Journal = {Biomaterials (UK)}, Volume = {27}, Number = {9}, Pages = {1930 - 5}, Year = {2006}, url = {http://dx.doi.org/10.1016/j.biomaterials.2005.10.018}, Keywords = {biological tissues;biomedical materials;DNA;enzymes;patient treatment;polymer gels;tissue engineering;}, Abstract = {Elastin-like polypeptides (ELPs) are a class of biocompatible, non-immunogenic and crosslinkable biomaterials that offer promise for use as an injectable scaffold for cartilage repair. In this study, an oligohistidine (His<sub>6</sub>) epitope tag was incorporated at the N-terminus of an ELP using recombinant DNA techniques to permit tracking without compromising on material biocompatibility. His<sub>6</sub>-tagged ELPs were successfully detected by Western blot analysis and quantified by ELISAs following digestion with trypsin. The mass of His<sub>6</sub> tagged ELP fragments freed from a crosslinked ELP hydrogel after digestion with trypsin correlated highly with hydrogel weight loss, providing evidence of the tag's capability to enable tracking of enzymatic degradation of the ELP hydrogel. The His<sub>6</sub> tag also facilitated recognition of crosslinked ELPs from background staining of articular cartilage. These results suggest that the His<sub>6</sub> epitope tag has the potential to track ELP scaffold loss independently of newly formed tissue mass for evaluating matrix remodeling in vivo. [All rights reserved Elsevier]}, Key = {8827248} } @article{8776598, Author = {Setton, L.A. and Betre, H. and Ong, S.R. and Guilak, F. and Chilkoti, A. and Fermor, B.}, Title = {Chondrocytic differentiation of human adipose-derived adult stem cells in elastin-like polypeptide}, Journal = {Biomaterials (UK)}, Volume = {27}, Number = {1}, Pages = {91 - 9}, Year = {2006}, url = {http://dx.doi.org/10.1016/j.biomaterials.2005.05.071}, Keywords = {biomedical materials;cellular biophysics;gels;genetic engineering;molecular biophysics;proteins;}, Abstract = {Human adipose derived adult stem (<i>h</i>ADAS) cells have the ability to differentiate into a chondrogenic phenotype in three-dimensional culture and media containing dexamethasone and TGF-<i>β</i>. The current study examined the potential of a genetically engineered elastin-like polypeptide (ELP) to promote the chondrocytic differentiation of <i>h</i>ADAS cells without exogenous chondrogenic supplements. <i>h</i>ADAS cells were cultured in ELP hydrogels in either chondrogenic or standard medium at 5% O<sub>2</sub> for up to 2 weeks. By day 14, constructs cultured in either medium exhibited significant increases in sulfated glycosaminoglycan (up to 100%) and collagen contents (up to 420%). Immunolabeling confirmed that the matrix formed consisted mainly of type II and not type I collagen. The composition of the constructs cultured in either medium did not differ significantly. To assess the effect of oxygen tension on the differentiation of the above constructs, samples were cultured in standard medium at either 5% or 20% O<sub>2</sub> for 7 days and their gene expression profile was evaluated using real time RT-PCR. In both cases, the <i>h</i>ADAS-ELP constructs upregulated SOX9 and type II collagen gene expression, while type I collagen was downregulated. However, constructs cultured in 20% O<sub>2</sub> highly upregulated type X collagen, which was not detected in the 5% O<sub>2</sub> cultures. The study suggests that ELP can promote chondrogenesis for <i>h</i>ADAS cells in the absence of exogenous TGF-<i>β</i>1 and dexamethasone, especially under low oxygen tension conditions. [All rights reserved Elsevier]}, Key = {8776598} } @booklet{Upton06, Author = {M. L. Upton and A. Hennerbichler and B. Fermor and F. Guilak and J. B. Weinberg and L. A. Setton}, Title = {Biaxial strain effects on cells from the inner and outer regions of the meniscus}, Journal = {Connective Tissue Research}, Volume = {47}, Number = {4}, Pages = {207 -- 214}, Year = {2006}, ISSN = {0300-8207}, Abstract = {During knee joint loading, the fibrocartilaginous menisci experience significant spatial variations in mechanical stimuli. Meniscus cells also exhibit significant variations in biosynthesis and gene expression depending on their location within the tissue. These metabolic patterns are consistent with a more chondrocytic phenotype for cells located within the avascular inner two-thirds compared with a more fibroblastic phenotype for cells within the vascularized outer periphery. The spatial distribution of cell biosynthesis and gene expression patterns within the meniscus suggest that cells may exhibit intrinsically different responses to mechanical stimuli. The objective of our study was to test for intrinsic differences in the responsiveness of these meniscus cell populations to an equivalent mechanical stimulus. Cellular biosynthesis and gene expression for extracellular matrix proteins in isolated inner and outer meniscus cells in monolayer were quantified following cyclic biaxial stretch. The results demonstrate that inner and outer meniscus cells exhibit significant differences in matrix biosynthesis and gene expression regardless of stretching condition. Both inner and outer meniscus cells responded to stretch with increased nitric oxide production and total protein synthesis. The results suggest that inner and outer meniscus cells may respond similarly to biaxial stretch in vitro with measures of biosynthesis and gene expression.}, Key = {Upton06} } @booklet{Mchale05, Author = {M. K. Mchale and L. A. Setton and A. Chilkoti}, Title = {Synthesis and in vitro evaluation of enzymatically cross-linked elastin-like polypeptide gels for cartilaginous tissue repair}, Journal = {Tissue Engineering}, Volume = {11}, Number = {11-12}, Pages = {1768 -- 1779}, Year = {2005}, Month = {November}, ISSN = {1076-3279}, Abstract = {Genetically engineered elastin-like polypeptide (ELP) hydrogels offer unique promise as scaffolds for cartilage tissue engineering because of the potential to promote chondrogenesis and to control mechanical properties. In this study, we designed and synthesized ELPs capable of undergoing enzyme-initiated gelation via tissue transglutaminase, with the ultimate goal of creating an injectable, in situ cross-linking scaffold to promote functional cartilage repair. Addition of the enzyme promoted ELP gel formation and chondrocyte encapsulation in a biocompatible process, which resulted in cartilage matrix synthesis in vitro and the potential to contribute to cartilage mechanical function in vivo. A significant increase in the accumulation of sulfated glycosaminoglycans was observed, and histological sections revealed the accumulation of a cartilaginous matrix rich in type II collagen and lacking in type I collagen, indicative of hyaline cartilage formation. These results provide evidence of chondrocytic phenotype maintenance for cells in the ELP hydrogels in vitro. In addition, the dynamic shear moduli of ELP hydrogels seeded with chondrocytes increased from 0.28 to 1.7 kPa during a 4-week culture period. This increase in the mechanical integrity of cross-linked ELP hydrogels suggests restructuring of the ELP matrix by deposition of functional cartilage extracellular matrix components.}, Key = {Mchale05} } @booklet{Alexopoulos05, Author = {L. G. Alexopoulos and L. A. Setton and F. Guilak}, Title = {The biomechanical role of the chondrocyte pericellular matrix in articular cartilage}, Journal = {Acta Biomaterialia}, Volume = {1}, Number = {3}, Pages = {317 -- 325}, Year = {2005}, Month = {May}, ISSN = {1742-7061}, Key = {Alexopoulos05} } @article{06049665755, Author = {McHale, Melissa K. and Setton, Lori A. and Chilkoti, Ashutosh}, Title = {Synthesis and in vitro evaluation of enzymatically cross-linked elastin-like polypeptide gels for cartilaginous tissue repair}, Journal = {Tissue Engineering}, Volume = {11}, Number = {11-12}, Pages = {1768 - 1779}, Year = {2005}, url = {http://dx.doi.org/10.1089/ten.2005.11.1768}, Keywords = {Hydrogels;Biosynthesis;Tissue;Enzyme immobilization;Cartilage;Mechanical properties;Gelation;Biocompatibility;Histology;Elastic moduli;}, Abstract = {Genetically engineered elastin-Iike polypeptide (ELP) hydrogels offer unique promise as scaffolds for cartilage tissue engineering because of the potential to promote chondrogenesis and to control mechanical properties. In this study, we designed and synthesized ELPs capable of undergoing enzyme-initiated gelation via tissue transglutaminase, with the ultimate goal of creating an injectable, in situ cross-linking scaffold to promote functional cartilage repair. Addition of the enzyme promoted ELP gel formation and chondrocyte encapsulation in a biocompatible process, which resulted in cartilage matrix synthesis in vitro and the potential to contribute to cartilage mechanical function in vivo. A significant increase in the accumulation of sulfated glycosaminoglycans was observed, and histological sections revealed the accumulation of a cartilaginous matrix rich in type II collagen and lacking in type I collagen, indicative of hyaline cartilage formation. These results provide evidence of chondrocytic phenotype maintenance for cells in the ELP hydrogels in vitro. In addition, the dynamic shear moduli of ELP hydrogels seeded with chondrocytes increased from 0.28 to 1.7 kPa during a 4-week culture period. This increase in the mechanical integrity of cross-linked ELP hydrogels suggests restructuring of the ELP matrix by deposition of functional cartilage extracellular matrix components. © Mary Ann Liebert, Inc.}, Key = {06049665755} } @article{06219888998, Author = {Haider, Mansoor A. and Schugart, Richard C. and Setton, Lori A. and Guilak, Farshid}, Title = {A mechano-chemical model for osmotic loading of an isolated chondron}, Journal = {Proceedings of the 2005 Summer Bioengineering Conference}, Volume = {2005}, Pages = {613 - 614}, Address = {Vail, CO, United States}, Year = {2005}, Key = {06219888998} } @article{06219889008, Author = {Haider, Mansoor A. and Nettles, Dana L. and Trabbic-Carlson, Kimberly and Chilkoti, Ashutosh and Setton, Lori A.}, Title = {Predictive modeling of polypeptide hydrogel mechanical properties for cartilage repair using artificial neural networks}, Journal = {Proceedings of the 2005 Summer Bioengineering Conference}, Volume = {2005}, Pages = {633 - 634}, Address = {Vail, CO, United States}, Year = {2005}, Key = {06219889008} } @article{05449455291, Author = {Guilak, Farshid and Alexopoulos, Leonidas G. and Haider, Mansoor A. and Ting-Beall, H. Ping and Setton, Lori A.}, Title = {Zonal uniformity in mechanical properties of the chondrocyte pericellular matrix: Micropipette aspiration of canine chondrons isolated by cartilage homogenization}, Journal = {Annals of Biomedical Engineering}, Volume = {33}, Number = {10}, Pages = {1312 - 1318}, Year = {2005}, url = {http://dx.doi.org/10.1007/s10439-005-4479-7}, Keywords = {Tissue;Mechanical properties;Cells;Flow of fluids;Matrix algebra;Biomechanics;Collagen;}, Abstract = {The pericellular matrix (PCM) is a region of tissue that surrounds chondrocytes in articular cartilage and together with the enclosed cells is termed the chondron. Previous studies suggest that the mechanical properties of the PCM, relative to those of the chondrocyte and the extracellular matrix (ECM), may significantly influence the stress-strain, physicochemical, and fluid-flow environments of the cell. The aim of this study was to measure the biomechanical properties of the PCM of mechanically isolated chondrons and to test the hypothesis that the Young's modulus of the PCM varies with zone of origin in articular cartilage (surface vs. middle/deep). Chondrons were extracted from articular cartilage of the canine knee using mechanical homogenization, and the elastic properties of the PCM were determined using micropipette aspiration in combination with theoretical models of the chondron as an elastic incompressible half-space, an elastic compressible bilayer, or an elastic compressible shell. The Young's modulus of the PCM was significantly higher than that reported for isolated chondrocytes but over an order of magnitude lower than that of the cartilage ECM. No significant differences were observed in the Young's modulus of the PCM between surface zone (24.0 ± 8.9 kPa) and middle/deep zone cartilage (23.2 ± 7.1 kPa). In combination with previous theoretical biomechanical models of the chondron, these findings suggest that the PCM significantly influences the mechanical environment of the chondrocyte in articular cartilage and therefore may play a role in modulating cellular responses to micromechanical factors. © 2005 Biomedical Engineering Society.}, Key = {05449455291} } @article{06219888808, Author = {Upton, Maureen L. and Laursen, Tod A. and Guilak, Farshid and Setton, Lori A.}, Title = {Finite element modeling of region-specific cell-matrix interactions in the meniscus}, Journal = {Proceedings of the 2005 Summer Bioengineering Conference}, Volume = {2005}, Pages = {229 - 230}, Address = {Vail, CO, United States}, Year = {2005}, Key = {06219888808} } @article{06219888810, Author = {Cao, Li and Youn, Inchan and Li, Yefu and Guilak, Farshid and Olsen, Bjorn R. and Setton, Lori A.}, Title = {Biphasic micro-indentation testing of mouse articular cartilage reveals functional changes in a type IX collagen knockout model of osteoarthritis}, Journal = {Proceedings of the 2005 Summer Bioengineering Conference}, Volume = {2005}, Pages = {233 - 234}, Address = {Vail, CO, United States}, Year = {2005}, Key = {06219888810} } @article{8999809, Author = {Boyd, L.M. and Richardson, W.J. and Chen, J. and Kraus, V.B. and Tewari, A. and Setton, L.A.}, Title = {Osmolarity regulates gene expression in intervertebral disc cells determined by gene array and real-time quantitative RT-PCR}, Journal = {Ann. Biomed. Eng. (USA)}, Volume = {33}, Number = {8}, Pages = {1071 - 7}, Year = {2005}, url = {http://dx.doi.org/10.1007/s10439-005-5775-y}, Keywords = {biochemistry;biodiffusion;biomembrane transport;genetics;molecular biophysics;neurophysiology;osmosis;proteins;}, Abstract = {Intervertebral disc (IVD) cells experience a broad range of physicochemical stimuli under physiologic conditions, including alterations in their osmotic environment. Cellular responses to altered osmolarity have been documented at the transcriptional and post-translational level, but mainly for extracellular matrix proteins. In this study, the gene expression profile of human IVD cells was quantified with gene array technology following exposure to increased osmolarity in order to capture the biological responses for a broad set of targets. A total of 42 genes were identified in IVD cells as significantly changed following culture under hyper-osmotic conditions. Gene expression patterns were verified using RT-PCR. Genes identified in this study include those related to cytoskeleton remodeling and stabilization (ephrin-B2, muskelin), as well as membrane transport (ion transporter SLC21A12, osmolyte transporter SLC5A3, monocarboxylic acid SLC16A6). An unexpected finding was the differential regulation of the gene for the neurotrophin, brain-derived neurotrophic factor, by hyper-osmotic stimuli that suggests a capability of IVD cells to respond to physicochemical stimuli with factors that may regulate discogenic pain}, Key = {8999809} } @article{8841799, Author = {Guilak, F. and Alexopoulos, L.G. and Setton, L.A.}, Title = {The biomechanical role of the chondrocyte pericellular matrix in articular cartilage}, Journal = {Acta Biomat. (UK)}, Volume = {1}, Number = {3}, Pages = {317 - 25}, Year = {2005}, url = {http://dx.doi.org/10.1016/j.actbio.2005.02.001}, Keywords = {biological tissues;biomechanics;cellular transport;finite element analysis;permeability;physiological models;stress-strain relations;Young's modulus;}, Abstract = {The pericellular matrix (PCM) is a narrow tissue region that surrounds chondrocytes in articular cartilage. Previous parametric studies of cell-matrix interactions suggest that the mechanical properties of the PCM relative to those of the extracellular matrix (ECM) can significantly affect the micromechanical environment of the chondrocyte. The goal of this study was to use recently quantified mechanical properties of the PCM in a biphasic finite element model of the cell-PCM-ECM structure to determine the potential influence of the PCM on the mechanical environment of the chondrocyte under normal and osteoarthritic conditions. Our findings suggest that the mismatch between the Young's moduli of PCM and ECM amplifies chondrocyte compressive strains and exhibits a significant stress shielding effect in a zone-dependent manner. Furthermore, the lower permeability of PCM relative to the ECM inhibits fluid flux near the cell by a factor of 30, and thus may have a significant effect on convective transport to and from the chondrocyte. Osteoarthritic changes in the PCM and ECM properties significantly altered the mechanical environment of the chondrocyte, leading to ~66% higher compressive strains and higher fluid flux near the cell. These findings provide further support for a potential biomechanical role for the chondrocyte PCM, and suggest that changes in the properties of the PCM with osteoarthritis may alter the stress-strain and fluid flow environment of the chondrocytes. [All rights reserved Elsevier]}, Key = {8841799} } @article{8419741, Author = {Alexopoulos, L.G. and Williams, G.M. and Upton, M.L. and Setton, L.A. and Guilak, F.}, Title = {Osteoarthritic changes in the biphasic mechanical properties of the chondrocyte pericellular matrix in articular cartilage}, Journal = {J. Biomech. (UK)}, Volume = {38}, Number = {3}, Pages = {509 - 17}, Year = {2005}, url = {http://dx.doi.org/10.1016/j.jbiomech.2004.04.012}, Keywords = {biomechanics;biorheology;bone;cellular biophysics;diseases;finite element analysis;orthopaedics;physiological models;Poisson ratio;viscoelasticity;Young's modulus;}, Abstract = {The pericellular matrix (PCM) is a narrow region of cartilaginous tissue that surrounds chondrocytes in articular cartilage. Previous modeling studies indicate that the mechanical properties of the PCM relative to those of the extracellular matrix (ECM) can significantly affect the stress-strain, fluid flow, and physicochemical environments of the chondrocyte, suggesting that the PCM plays a biomechanical role in articular cartilage. The goals of this study were to measure the mechanical properties of the PCM using micropipette aspiration coupled with a linear biphasic finite element model, and to determine the alterations in the mechanical properties of the PCM with osteoarthritis (OA). Using a recently developed isolation technique, chondrons (the chondrocyte and its PCM) were mechanically extracted from non-degenerate and osteoarthritic human cartilage. The transient mechanical behavior of the PCM was well-described by a biphasic model, suggesting that the viscoelastic response of the PCM is attributable to flow-dependent effects, similar to that of the ECM. With OA, the mean Young's modulus of the PCM was significantly decreased (38.7±16.2kPa vs. 23.5±12.9kPa, p<0.001), and the permeability was significantly elevated (4.19±3.78×10<sup>-17</sup>m<sup>4</sup>/Ns vs. 10.2±9.38×10<sup>-17</sup>m<sup>4</sup>/Ns, p<0.001). The Poisson's ratio was similar for both non-degenerate and OA PCM (0.044±0.063 vs. 0.030±0.068, p>0.6). These findings suggest that the PCM may undergo degenerative processes with OA, similar to those occurring in the ECM. In combination with previous theoretical models of cell-matrix interactions in cartilage, our findings suggest that changes in the properties of the PCM with OA may have an important influence on the biomechanical environment of the chondrocyte. [All rights reserved Elsevier]}, Key = {8419741} } @article{7956034, Author = {Gilchrist, C.L. and Xia, J.Q. and Setton, L.A. and Hsu, E.W.}, Title = {High-resolution determination of soft tissue deformations using MRI and first-order texture correlation}, Journal = {IEEE Trans. Med. Imaging (USA)}, Volume = {23}, Number = {5}, Pages = {546 - 53}, Year = {2004}, url = {http://dx.doi.org/10.1109/TMI.2004.825616}, Keywords = {biological tissues;biomechanics;biomedical MRI;deformation;image texture;medical image processing;strain measurement;}, Abstract = {Mechanical factors such as deformation and strain are thought to play important roles in the maintenance, repair, and degeneration of soft tissues. Determination of soft tissue static deformation has traditionally only been possible at a tissue's surface, utilizing external markers or instrumentation. Texture correlation is a displacement field measurement technique which relies on unique image patterns within a pair of digital images to track displacement. The technique has recently been applied to MR images, indicating the possibility of high-resolution displacement and strain field determination within the mid-substance of soft tissues. However, the utility of MR texture correlation analysis may vary amongst tissue types depending on their underlying structure, composition, and contrast mechanism, which give rise to variations in texture with MRI. In this study, we investigate the utility of a texture correlation algorithm with first-order displacement mapping terms for use with MR images, and suggest a novel index of image "roughness" as a way to decrease errors associated with the use of texture correlation for intra-tissue strain measurement with MRI. We find that a first-order algorithm can significantly reduce strain measurement error, and that an image "roughness" index correlates with displacement measurement error for a variety of imaging conditions and tissue types}, Key = {7956034} } @article{8184668, Author = {Nettles, D.L. and Vail, T.P. and Morgan, M.T. and Grinstaff, M.W. and Setton, L.A.}, Title = {Photocrosslinkable hyaluronan as a scaffold for articular cartilage repair}, Journal = {Ann. Biomed. Eng. (USA)}, Volume = {32}, Number = {3}, Pages = {391 - 7}, Year = {2004}, url = {http://dx.doi.org/10.1023/B:ABME.0000017552.65260.94}, Keywords = {biochemistry;biodiffusion;biomechanics;biomedical materials;bone;cellular biophysics;diseases;gels;molecular biophysics;organic compounds;shear modulus;tissue engineering;}, Abstract = {Hyaluronan-based scaffolds are of interest for tissue-engineered cartilage repair due to an important role for hyaluronan in cartilage development and function. In this study, an in situ photocrosslinkable hyaluronan (HA-MA) was developed and evaluated as a scaffold for articular cartilage repair. Chondrocytes were encapsulated in crosslinked HA-MA and evaluated for their ability to synthesize cartilaginous matrix in vitro. The mechanical and physical properties of the crosslinked HA-MA hydrogels were similar to that of other hydrogels, with compressive and dynamic shear moduli of 0.6 and 0.3 kPa, respectively, and diffusion coefficients of 600-8000 μm<sup>2</sup>/s depending on molecular weight. Chondrocytes remained rounded in the HA-MA hydrogels in vitro, and accumulated significant amounts of cartilaginous matrix. Osteochondral defects filled with HA-MA were infiltrated with cells, appeared to integrate well with native tissue, and also accumulated substantial cartilaginous matrix by 2 weeks after surgery. In summary, photocrosslinkable HA-MA promoted the retention of the chondrocytic phenotype and cartilage matrix synthesis for encapsulated chondrocytes in vitro and accelerated healing in an in vivo osteochondral defect model}, Key = {8184668} } @article{03267515018, Author = {Trabbic-Carlson, Kimberly and Setton, Lori A. and Chilkoti, Ashutosch}, Title = {Swelling and mechanical behaviors of chemically cross-linked hydrogels of elastin-like polypeptides}, Journal = {Biomacromolecules}, Volume = {4}, Number = {3}, Pages = {572 - 580}, Year = {2003}, url = {http://dx.doi.org/10.1021/bm025671z}, Keywords = {Hydrogels;Crosslinking;Synthesis (chemical);Stiffness;Molecular weight;}, Abstract = {Genetically engineered elastin-like polypeptides consisting of Val-Pro-Gly-X-Gly repeats, where X was chosen to be Lys every 7 or 17 pentapeptides (otherwise X was Val), were synthesized and expressed in E. coli, purified, and chemically cross-linked using tris-succinimidyl aminotriacetate to produce hydrogels. Swelling experiments indicate hydrogel mass decreases by 80-90% gradually over an approximate 50 °C temperature range. Gels ranged in stiffness from 0.24 to 3.7 kPa at 7 °C and from 1.6 to 15 kPa at 37 °C depending on protein concentration, lysine content, and molecular weight. Changes in gel stiffness and loss angle with cross-linking formulation suggest a low-temperature gel structure that is nearly completely elastic, where force is transmitted almost exclusively through fully extended polypeptide chains and chemical crosslinks, and a high-temperature gel structure, where ELP chains are contracted and force is transmitted through chemical cross-links as well as frictional contact between polypeptide chains.}, Key = {03267515018} } @article{03457714515, Author = {Upton, Maureen L. and Chen, Jun and Guilak, Farshid and Setton, Lori A.}, Title = {Differential effects of static and dynamic compression on meniscal cell gene expression}, Journal = {Journal of Orthopaedic Research}, Volume = {21}, Number = {6}, Pages = {963 - 969}, Year = {2003}, url = {http://dx.doi.org/10.1016/S0736-0266(03)00063-9}, Keywords = {Cell culture;Genetic engineering;Metabolism;Proteins;Compressive stress;Biosynthesis;}, Abstract = {Cells of the meniscus are exposed to a wide range of time-varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well-controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real-time RT-PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08-0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin ( [similar to] 2.1 fold-difference) and type II collagen ( [similar to] 4.0 fold-difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression ( [similar to] 4.5 fold-difference), as did mRNA levels for both types I ( [similar to] 3.3 fold-difference) and II collagen ( [similar to] 4.0 fold-difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold-increase in mRNA levels for collagenase, or MMP-1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.}, Key = {03457714515} } @article{7590479, Author = {Baer, A.E. and Laursen, T.A. and Guilak, F. and Setton, L.A.}, Title = {The micromechanical environment of intervertebral disc cells determined by a finite deformation, anisotropic, and biphasic finite element model}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {125}, Number = {1}, Pages = {1 - 11}, Year = {2003}, url = {http://dx.doi.org/10.1115/1.1532790}, Keywords = {biomechanics;cellular biophysics;finite element analysis;micromechanics;physiological models;viscoelasticity;}, Abstract = {Cellular response to mechanical loading varies between the anatomic zones of the intervertebral disc. This difference may be related to differences in the structure and mechanics of both cells and extracellular matrix, which are expected to cause differences in the physical stimuli (such as pressure, stress, and strain) in the cellular micromechanical environment. In this study, a finite element model was developed that was capable of describing the cell micromechanical environment in the intervertebral disc. The model was capable of describing a number of important mechanical phenomena: flow-dependent viscoelasticity using the biphasic theory for soft tissues; finite deformation effects using a hyperelastic constitutive law for the solid phase; and material anisotropy by including a fiber-reinforced continuum law in the hyperelastic strain energy function. To construct accurate finite element meshes, the in situ geometry of IVD cells were measured experimentally using laser scanning confocal microscopy and three-dimensional reconstruction techniques. The model predicted that the cellular micromechanical environment varies dramatically between the anatomic zones, with larger cellular strains predicted in the anisotropic anulus fibrosus and transition zone compared to the isotropic nucleus pulposus. These results suggest that deformation related stimuli may dominate for anulus fibrosus and transition zone cells, while hydrostatic pressurization may dominate in the nucleus pulposus. Furthermore, the model predicted that micromechanical environment is strongly influenced by cell geometry, suggesting that the geometry of IVD cells in situ may be an adaptation to reduce cellular strains during tissue loading}, Key = {7590479} } @article{7614356, Author = {Upton, M.L. and Chen, J. and Guilak, F. and Setton, L.A.}, Title = {Static compression inhibits matrix protein gene expression and increases collagenase gene expression in the meniscus}, Journal = {Conference Proceedings. Second Joint EMBS-BMES Conference 2002. 24th Annual International Conference of the Engineering in Medicine and Biology Society. Annual Fall Meeting of the Biomedical Engineering Society (Cat. No.02CH37392)}, Volume = {vol.1}, Pages = {438 - 9}, Address = {Houston, TX, USA}, Year = {2002}, url = {http://dx.doi.org/10.1109/IEMBS.2002.1136884}, Keywords = {biological tissues;biomechanics;genetics;orthopaedics;proteins;}, Abstract = {The biological response of the meniscus to static compression was quantified as changes in gene expression levels for relevant extracellular matrix proteins. Decreased mRNA levels for decorin and type I collagen were observed, as well as increased mRNA levels for the matrix metalloproteinase MMP-1. These findings demonstrate that the response of the meniscus to mechanical stimuli may be regulated in part at the transcriptional level}, Key = {7614356} } @article{7626542, Author = {Betre, H. and Chilkoti, A. and Setton, L.A.}, Title = {A two-step chondrocyte recovery system based on thermally sensitive elastin-like polypeptide scaffolds for cartilage tissue engineering}, Journal = {Conference Proceedings. Second Joint EMBS-BMES Conference 2002. 24th Annual International Conference of the Engineering in Medicine and Biology Society. Annual Fall Meeting of the Biomedical Engineering Society (Cat. No.02CH37392)}, Volume = {vol.1}, Pages = {829 - 30}, Address = {Houston, TX, USA}, Year = {2002}, url = {http://dx.doi.org/10.1109/IEMBS.2002.1137096}, Keywords = {biological tissues;biomedical materials;biothermics;cellular biophysics;monolayers;proteins;}, Abstract = {A "two step" tissue engineering strategy was developed to promote rapid matrix accumulation in cartilage constructs in vitro. Chondrocytes expanded in monolayer were encapsulated and cultured in a genetically engineered, thermally sensitive elastin-like polypeptide (ELP) for ten days. The resulting cell-matrix pellets were recovered from the ELP and cultured on inserts for up to four weeks, where nutrient diffusion was not impeded by the presence of the scaffold. Approximately two-milligram (dry weight) tissue was generated that resembles native articular cartilage in histological appearance and biochemical composition. These results suggest that rapid and large cartilage construct formation is possible in vitro, following a period of early incubation and recovery from the thermally responsive ELP}, Key = {7626542} } @article{02407118389, Author = {Wyland, Douglas J. and Guilak, Farshid and Elliott, Dawn M. and Setton, Lori A. and Vail, Thomas P.}, Title = {Chondropathy after meniscal tear or partial meniscectomy in a canine model}, Journal = {Journal of Orthopaedic Research}, Volume = {20}, Number = {5}, Pages = {996 - 1002}, Year = {2002}, url = {http://dx.doi.org/10.1016/S0736-0266(02)00022-0}, Keywords = {Cartilage;Tensile strength;}, Abstract = {A primary goal in considering treatment for meniscal injuries is the preservation of the health of the articular cartilage. However, the chondroprotective effects of various techniques for meniscal injury treatments are unknown. We used a canine model to quantify articular cartilage degeneration in the medial compartment of the canine knee, resulting from a surgically created tear or a partial meniscectomy (PM) of the posterior region of the medial meniscus (each group, n = 10). After sacrifice at 12 weeks, the development of gross chondropathy and the changes in cartilage tensile stiffness were quantified, and correlations between these measurements were examined. Both treatment surgical treatment groups caused significantly greater gross chondropathy as compared to the unoperated contralateral controls. Cartilage tensile stiffness was significantly lower than unoperated controls by nearly 28% in both experimental groups. However, there were no significant differences observed between the gross chondropathy or the cartilage mechanical property changes between the experimental groups. Importantly, the severity of gross chondropathy was found to significantly correlate with the decrement in tensile stiffness properties of the articular cartilage. These findings indicate that significant degeneration of canine articular cartilage develops to a similar degree in the presence of a partially healed meniscus tear or a PM of the knee. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.}, Key = {02407118389} } @article{02056841813, Author = {Narmoneva, Daria A. and Cheung, Herman S. and Wang, Jean Y. and Howell, David S. and Setton, Lori A.}, Title = {Altered swelling behavior of femoral cartilage following joint immbolization in a canine model}, Journal = {Journal of Orthopaedic Research}, Volume = {20}, Number = {1}, Pages = {83 - 91}, Year = {2002}, url = {http://dx.doi.org/10.1016/S0736-0266(01)00076-6}, Keywords = {Bone;Collagen;Sodium chloride;Biomechanics;Swelling;Metabolism;Volume fraction;Physiological models;}, Abstract = {Periods of reduced joint loading have been shown to induce changes in the biochemical composition, metabolism and mechanics of articular cartilage. In this study, changes in cartilage swelling behavior were studied following a 4-week period of joint immobilization, using a recently developed osmotic loading technique [J. Biomech. 32 (1999) 401-408]. The magnitude and distribution of swelling strains were measured in cartilage-bone samples equilibrated in physiological and hypotonic saline, relative to a hypertonic reference NaCl solution. Physicochemical parameters (glycosaminoglycan fixed charge density and water volume fraction) were determined in site-matched cartilage samples. The experimental data for swelling strains, fixed charge density and water volume fraction were used with a triphasic mechano-chemical theory [J. Biomech. Eng. 113 (1991) 245-258] to determine the effect of joint immobilization on the tensile modulus of the cartilage solid matrix. Four weeks of immobilization resulted in a significant increase in the magnitude of swelling-induced strains, and a significant decrease in fixed charge density in cartilage, as compared with the contralateral controls. Joint immobilization also resulted in decreases in values for the modulus of cartilage, as compared with the contralateral controls. Our results suggest that 4 weeks of joint immobilization had a significant effect on cartilage mechanical function that may be linked to collagen changes in the cartilage extracellular matrix. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.}, Key = {02056841813} } @article{7281970, Author = {LeRoux, M.A. and Setton, L.A.}, Title = {Experimental and biphasic FEM determinations of the material properties and hydraulic permeability of the meniscus in tension}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {124}, Number = {3}, Pages = {315 - 21}, Year = {2002}, url = {http://dx.doi.org/10.1115/1.1468868}, Keywords = {biological tissues;biomechanics;finite element analysis;orthopaedics;permeability;physiological models;Poisson ratio;stress relaxation;stress-strain relations;Young's modulus;}, Abstract = {Tensile tests and biphasic finite element modeling were used to determine a set of transversely isotropic properties for the meniscus, including the hydraulic permeability coefficients and solid matrix properties. Stress-relaxation tests were conducted on planar samples of canine meniscus samples of different orientations, and the solid matrix properties were determined from equilibrium data. A 3-D linear biphasic and tranversely isotropic finite element model was developed to model the stress-relaxation behavior of the samples in tension, and optimization was used to determine the permeability coefficients, k<sub>1</sub> and k<sub>2</sub>, governing fluid flow parallel and perpendicular to the collagen fibers, respectively. The collagen fibrillar orientation was observed to have an effect on the Young's moduli (E<sub>1</sub>=67.8 MPa, E<sub>2</sub>=11.1 MPa) and Poisson's ratios (ν<sub>12</sub>=2.13, ν<sub>21</sub>=1.50, ν<sub>23</sub>=1.02). However, a significant effect of anisotropy on permeability was not detected (k<sub>1</sub>=0.09×10<sup>-16</sup> m<sup>4</sup>/Ns, k<sub>2</sub>=0.10×10<sup>-16</sup> m<sup>4</sup>/Ns). The low permeability values determined in this study provide insight into the extent of fluid pressurization in the meniscus and will impact modeling predictions of load support in the meniscus}, Key = {7281970} } @article{7237377, Author = {Elliott, D.M. and Narmoneva, D.A. and Setton, L.A.}, Title = {Direct measurement of the Poisson's ratio of human patella cartilage in tension}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {124}, Number = {2}, Pages = {223 - 8}, Year = {2002}, url = {http://dx.doi.org/10.1115/1.1449905}, Keywords = {biological tissues;biomechanics;biomedical measurement;Poisson ratio;proteins;}, Abstract = {Articular cartilage has been shown to exhibit large transverse contractions when loaded in tension, suggesting the existence of large values for the Poisson's ratio. Previous studies have suggested that this effect is dependent on amplitude of applied strain, so that a single Poisson's ratio may not be sufficient to describe cartilage behavior. In this study, the Poisson's ratio (ν), toe region modulus (E<sub>o</sub>), and linear region modulus (E) of human patellar articular cartilage were calculated in simple tension tests from optical analysis of the two-dimensional strain fields at equilibrium. The Poisson's ratio was found to be independent of strain due to the absence of viscoelastic effects during testing. The Poisson's ratio was found to be significantly higher in the surface zone (1.87±1.11, p<0.01) than in the middle zone (0.62±0.23), with no significant correlation of ν with age of the cartilage. In general, values for Poisson's ratio were greater than 0.5, suggesting cartilage behavior in tension deviates from isotropy. Reported values for the Poisson's ratio of cartilage in compression have been much lower than values measured here in tension, reflecting a mechanical contribution of the collagen fibers to anisotropy in tension but not compression. The toe-region modulus (E<sub>o</sub>) was significantly higher in the surface zone (4.51±2.78 MPa, n=8) compared to the middle zone (2.51±1.93 MPa, n=10). In addition, the linear-region modulus (E) in the surface zone, but not middle zone (3.42±2.17 MPa, n=10), was found to correlate with age (R=0.97, p<0.02) with values of surface zone E equal to 23.92±12.29 MPa (n=5) for subjects under 70 yr of age, and 4.27±2.89 MPa (n=3) for subjects over 70 yr. Moduli values and trends with depth were consistent with previous studies of human and animal cartilage. From direct measures of two independent material properties, ν and E, we calculated a shear modulus, G, which had not been previously reported for cartilage from tensile testing. Calculated values for surface zone G were 3.64±1.80 MPa for subjects under 70 yr old and 0.96±0.69 MPa for subjects over 70 yr old, and were significantly higher in the surface zone than in the middle zone (1.10±0.78 MPa). This study provides an intrinsic measure for the Poisson's ratio of articular cartilage and its dependence on depth which will be important in understanding the nonlinear tension-compression and anisotropic behaviors of articular cartilage}, Key = {7237377} } @article{7265233, Author = {Meng, X.N. and LeRoux, M.A. and Laursen, T.A. and Setton, L.A.}, Title = {A nonlinear finite element formulation for axisymmetric torsion of biphasic materials}, Journal = {Int. J. Solids Struct. (UK)}, Volume = {39}, Number = {4}, Pages = {879 - 95}, Year = {2002}, url = {http://dx.doi.org/10.1016/S0020-7683(01)00249-9}, Keywords = {biological tissues;biomechanics;biorheology;deformation;finite element analysis;torsion;viscoelasticity;}, Abstract = {Presents a finite element formulation for describing the large deformation torsional response of biphasic materials, with specific application to prediction of nonlinear coupling between torsional deformation and fluid pressurization in articular cartilage. Due to the use of a cylindrical coordinate system, a particular challenge arises in the linearization of the weak form. The torsional axisymmetric case considered gives rise to additional geometric terms, which are important for the robustness of the numerical implementation and that would not be present in a Cartesian formulation. A detailed derivation of this linearization process is given, couched in the context of a variational formulation suitable for finite element implementation. A series of numerical parametric studies are presented and compared to experimental measurements of the time dependent response of cartilage}, Key = {7265233} } @article{7155395, Author = {Narmoneva, D.A. and Wang, J.Y. and Setton, L.A.}, Title = {A noncontacting method for material property determination for articular cartilage from osmotic loading}, Journal = {Biophys. J. (USA)}, Volume = {81}, Number = {6}, Pages = {3066 - 76}, Year = {2001}, Keywords = {biological techniques;biological tissues;biomechanics;optimisation;osmosis;physiological models;swelling;}, Abstract = {Articular cartilage is one of several biological tissues in which swelling effects are important in tissue mechanics and function, and may serve as an indicator of degenerative joint disease. This work presents a new approach to quantify swelling effects in articular cartilage, as well as to determine the material properties of cartilage from a simple free-swelling test. Samples of nondegenerate and degenerate human patellar cartilage were subjected to osmotic loading by equilibrating the tissue in solutions of varying osmolarity. The resulting swelling-induced strains were measured using a noncontacting optical method. A theoretical formulation of articular cartilage in a free-swelling configuration was developed based on an inhomogeneous, triphasic mechano-chemical model. Optimization of the model predictions to the experimental data was performed to determine two parameters descriptive of material stiffness at the surface and deeper cartilage layers, and a third parameter descriptive of thickness of the cartilage surface layer. These parameters were used to determine the thickness-averaged uniaxial modulus of cartilage, H<sub>A</sub>. The obtained values for H<sub>A</sub> were similar to those for the tensile modulus of human cartilage reported in the literature. Degeneration resulted in an increase in thickness of the region of "apparent cartilage softening," and a decrease in the value for uniaxial modulus at this layer. These findings provide important evidence that collagen matrix disruption starts at the articular surface and progresses into the deeper layers with continued degeneration. These results suggest that the method provides a means to quantify the severity and depth of degenerative changes in articular cartilage. This method may also be used to determine material properties of cartilage in small joints in which conventional testing methods are difficult to apply}, Key = {7155395} } @article{01216510489, Author = {Baer, A.E. and Wang, J.Y. and Kraus, V.B. and Setton, L.A.}, Title = {Collagen gene expression and mechanical properties of intervertebral disc cell-alginate cultures}, Journal = {Journal of Orthopaedic Research}, Volume = {19}, Number = {1}, Pages = {2 - 10}, Year = {2001}, url = {http://dx.doi.org/10.1016/S0736-0266(00)00003-6}, Keywords = {Tissue culture;Genes;RNA;Shear stress;}, Abstract = {Cells of the intervertebral disc have a limited capacity for matrix repair that may contribute to the onset and progression of degenerative disc changes. In this study, the biosynthetic capacity of cells isolated from specific regions of the porcine intervertebral disc was evaluated in vitro. Using a competitive reverse transcription-polymerase chain reaction technique, gene expression levels for types I and II collagen were quantified in cells cultured for up to 21 d in a three-dimensional alginate culture system and compared to levels obtained for cells in vivo. The mechanical properties of cell-alginate constructs were measured in compression and shear after periods of culture up to 16 weeks. Cells from the anulus fibrosus expressed the most type I collagen mRNA in vivo and in vitro, while cells from the transition zone expressed the most type II collagen mRNA in vivo and in vitro. Mechanical testing results indicate that a mechanically functional matrix did not form at any time during the culture period; rather, decreases of up to 50% were observed in the compressive and shear moduli of the cell-alginate constructs compared to alginate with no cells. Together with results of prior studies, these results suggest that intervertebral disc cells maintain characteristics of their phenotype when cultured in alginate, but the molecules they synthesize are not able to form a mechanically functional matrix in vitro. © 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.}, Key = {01216510489} } @article{03477739774, Author = {Baer, Anthony E. and Grinstaff, Mark W. and Smeds, Kimberly A. and Boyd, Lawrence M. and Setton, Lori A.}, Title = {Nonlinear finite element modeling of cell mechanical environment in hyorogels for intervertebral disc repair}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {50}, Pages = {113 - 114}, Address = {Snowbird, UT, United States}, Year = {2001}, Keywords = {Cell culture;Tissue;Hydrogels;Finite element method;Mathematical models;}, Abstract = {The nonlinear finite element modeling of cell mechanical environment in hydrogels for intervertebral disc (IVD) repair was studied. Two hydrogels were studied for tissue-engineered IVD repair. The results demonstrated that the micromechanical environment of an IVD cell embedded in a three-dimensional hydrogel is different from that of a cell in its native matrix.}, Key = {03477739774} } @article{03477740103, Author = {Baer, Anthony E. and Laursen, Tod A. and Setton, Lori A.}, Title = {A finite-deformation, anisotropic, biphasic finite element model of cell-matrix interactions in the intervertebral disc}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {50}, Pages = {799 - 800}, Address = {Snowbird, UT, United States}, Year = {2001}, Keywords = {Deformation;Anisotropy;Strain;Stress relaxation;Computational complexity;Finite element method;}, Abstract = {The finite deformation, anisotropic, biphasic finite element model of cell matrix interactions in the intervertebral disc was discussed. The model was used as a reference for validation of the nonlinear FEM predictions at equilibrium. The results suggested that zonal differences in cell micromechanical environment play a role in known differences in the biosynthetic response of the disc cells.}, Key = {03477740103} } @article{03477739982, Author = {Meng, X.N. and LeRoux, M.A. and Setton, L.A. and Laursen, T.A.}, Title = {Biphasic finite element formulation for modeling nonlinear response of articular cartilage to torsion}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {50}, Pages = {549 - 550}, Address = {Snowbird, UT, United States}, Year = {2001}, Keywords = {Torsional stress;Shear stress;Stress relaxation;Pressure effects;Elasticity;Elastic moduli;Mechanical permeability;Finite element method;Tensors;Nonlinear equations;Linearization;Computer simulation;}, Abstract = {A biphasic finite element formulation for predicting the coupling between pure torsion and normal stress effects in articular cartilage was presented. Both the computational and experimental data showed a transient normal stress effect arising from torsion that was lower in magnitude that the shear stress. Finite element results demonstrated that the normal stress during stress-relaxation arose from fluid pressurization.}, Key = {03477739982} } @article{03477740126, Author = {LeRoux, Michelle A. and Upton, Maureen L. and Laursen, Tod A. and Setton, Lori A.}, Title = {Biphasic finite element modeling of tear effects on the mechanics of the meniscus}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {50}, Pages = {851 - 852}, Address = {Snowbird, UT, United States}, Year = {2001}, Keywords = {Blood;Stress analysis;Strain;Anisotropy;Finite element method;Galerkin methods;Mathematical models;}, Abstract = {The biphasic finite element (FE) modeling of tear effects on the mechanics of the meniscus was studied. FE studied of the normal meniscus were used to predict the spatially varying stress-strain rate within the meniscus. These studies also demonstrate the importance of fluid-solid interactions in governing load-support and function of the meniscus was also demonstrated.}, Key = {03477740126} } @article{6998102, Author = {Elliott, D.M. and Setton, L.A.}, Title = {Anisotropic and inhomogeneous tensile behavior of the human anulus fibrosus: experimental measurement and material model predictions}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {123}, Number = {3}, Pages = {256 - 63}, Year = {2001}, url = {http://dx.doi.org/10.1115/1.1374202}, Keywords = {biological tissues;biomechanics;elastic moduli;physiological models;Poisson ratio;proteins;}, Abstract = {The anulus fibrosus (AF) of the intervertebral disc exhibits spatial variations in structure and composition that give rise to both anisotropy and inhomogeneity in its material behaviors in tension. In this study, the tensile moduli and Poisson's ratios were measured in samples of human AF along circumferential, axial, and radial directions at inner and outer sites. There was evidence of significant inhomogeneity in the linear-region circumferential tensile modulus (17.4±14.3 MPa versus 5.6±4.7 MPa, outer versus inner sites) and the Poisson's ratio ν<sub>21</sub> (0.67±0.22 versus 1.6±0.7, outer versus inner), but not in the axial modulus (0.8±0.9 MPa) or the Poisson's ratios ν<sub>12</sub> (1.8±1.4) or ν<sub>13</sub> (0.6±0.7). These properties were implemented in a linear anisotropic material model of the AF to determine a complete set of model properties and to predict material behaviors for the AF under idealized kinematic states. These predictions demonstrate that interactions between fiber populations in the multilamellae AF significantly contribute to the material behavior, suggesting that a model for the AF as concentric and physically isolated lamellae may not be appropriate}, Key = {6998102} } @article{00065216862, Author = {Lindhorst, E. and Vail, T.P. and Guilak, F. and Wang, H. and Setton, L.A. and Vilim, V. and Kraus, V.B.}, Title = {Longitudinal characterization of synovial fluid biomarkers in the canine meniscectomy model of osteoarthritis}, Journal = {Journal of Orthopaedic Research}, Volume = {18}, Number = {2}, Pages = {269 - 280}, Year = {2000}, Keywords = {Tissue;Diseases;Joints (anatomy);Surgery;Proteins;Blood vessels;}, Abstract = {Damage to the meniscus can lead to posttraumatic osteoarthritis. Early markers of joint injury and tissue disease may be useful in developing and administering clinical treatment. We investigated the effects of total medial meniscectomy on biomarkers measured serially in synovial lavage fluid each month for 3 months. Following meniscectomy in dogs, four biomarkers were evaluated: cartilage oligomeric matrix protein, keratan sulfate epitope (5D4), the 3B3(-) neoepitope of chondroitin-6-sulfate, and the 3B3(+) chondroitinase-generated epitope of chondroitin-6-sulfate. Meniscectomy led to statistically significant elevations of all four biomarkers, with levels peaking at 4 weeks. By 12 weeks, the level of the 5D4 epitope returned to the preoperative baseline level whereas that of cartilage oligomeric matrix protein, 3B3(-), and 3B3(+) remained above the baseline. Concentrations of these biomarkers in the knees not operated on did not change significantly from the baseline. The levels of cartilage oligomeric matrix protein and 3B3(-) relative to 3B3(+) remained constant in all knees. In contrast, the level of 5D4 relative to 3B3(+) declined over time in the knee operated on but remained constant in the knee not operated on. These results demonstrate a quantitative change in the molecular components of synovial fluid after meniscectomy, as well as qualitative change evinced by an alteration in the relative proportions of these epitopes. Extensive analyses showed a strong correlation between serum levels of 3B3(-) from the femoral and cephalic veins; however, serum 3B3(-) was not correlated with synovial fluid 3B3(-). These findings support the hypothesis that the concentrations of select cartilage biomarkers in synovial fluid are altered following meniscectomy and are promising tools for objectively monitoring the induction of osteoarthritis in this model system.}, Key = {00065216862} } @article{00095320395, Author = {LeRoux, Michelle A. and Arokoski, Jari and Vail, T. Parker and Guilak, Farshid and Hyttinen, Mika M. and Kiviranta, Ilkka and Setton, Lori A.}, Title = {Simultaneous changes in the mechanical properties, quantitative collagen organization, and proteoglycan concentration of articular cartilage following canine meniscectomy}, Journal = {Journal of Orthopaedic Research}, Volume = {18}, Number = {3}, Pages = {383 - 392}, Year = {2000}, Keywords = {Orthopedics;Living systems studies;Collagen;Densitometers;Light polarization;Optical microscopy;Microstructure;Molecular structure;Biomechanics;}, Abstract = {The mechanical properties and microstructure of articular cartilage from the canine tibial plateau were studied 12 weeks after total medial meniscectomy. The organization of the birefringent collagen network was measured with quantitative polarized light microscopy to determine the thickness and the degree of organization of the superficial and deep zones. The zonal concentration of sulfated glycosaminoglycan was quantified with digital densitometry of safranin-O staining. Equilibrium compressive and shear properties, as well as dynamic shear properties, were measured at sites adjacent to those of microstructural analysis. The results evinced significant loss of cartilage function following meniscectomy, with decreases of 20-50% in the compressive and shear moduli. There was no evidence of alterations in the degree of collagen fibrillar organization, although a complete loss of the surface zone was seen in 60% of the samples that underwent meniscectomy. Meniscectomy resulted in a decreased concentration of sulfated glycosaminoglycan, and significant positive correlations were found between the equilibrium compressive modulus and the glycosaminoglycan content. Furthermore, the shear properties of cartilage correlated directly with collagen fibrillar organization measured at the superficial zone of corresponding sites. These findings demonstrate that meniscectomy leads to impaired mechanical function of articular cartilage, with significant evidence of quantitative correlations between cartilage microstructure and mechanics.}, Key = {00095320395} } @article{6676926, Author = {Baer, A.E. and Setton, L.A.}, Title = {The micromechanical environment of intervertebral disc cells: effect of matrix anisotropy and cell geometry predicted by a linear model}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {122}, Number = {3}, Pages = {245 - 51}, Year = {2000}, url = {http://dx.doi.org/10.1115/1.429655}, Keywords = {biomechanics;cellular biophysics;physiological models;}, Abstract = {Cells of the intervertebral disc exhibit spatial variations in phenotype and morphology that may be related to differences in their local mechanical environments. In this study, the stresses, strains, and dilatations in and around cells of the intervertebral disc were studied with an analytical model of the cell as a mechanical inclusion embedded in a transversely isotropic matrix. In response to tensile loading of the matrix, the local mechanical environment of the cell differed among the anatomic regions of the disc and was strongly influenced by changes in both matrix anisotropy and parameters of cell geometry. The results of this study suggest that the local cellular mechanical environment may play a role in determining both cell morphology <i>in</i> <i>situ</i> and the inhomogeneous response to mechanical loading observed in cells of the disc}, Key = {6676926} } @article{6608606, Author = {Elliott, D.M. and Setton, L.A.}, Title = {A linear material model for fiber-induced anisotropy of the anulus fibrosus}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {122}, Number = {2}, Pages = {173 - 9}, Year = {2000}, url = {http://dx.doi.org/10.1115/1.429639}, Keywords = {biological tissues;biomechanics;fibres;physiological models;}, Abstract = {The anulus fibrosus (AF) is a lamellar, fibrocartilaginous component of the intervertebral disc, which exhibits highly anisotropic behaviors in tension. These behaviors arise from the material's unique collagen structure. We have investigated the use of a linear, fiber-induced anisotropic model for the AF using a quadratic strain energy density formulation with an explicit representation of the collagen fiber populations. We have proposed a representative set of intrinsic material properties using independent datasets of the AF from the literature and appropriate thermodynamic constraints. The model was validated by comparing predictions with previous experimental data for AF behavior and its dependence on fiber angle. The model predicts that compressible effects may exist for the AF, and suggests that physical effects of the equivalent “matrix,” “fiber,” “fiber-matrix,” and “fiber-fiber,” interactions may be important contributors to the mechanical behavior of the AF}, Key = {6608606} } @article{00275178035, Author = {Baer, Anthony E. and Wang, Jean Y. and Setton, Lori A.}, Title = {Mechanical properties of matrix synthesized by intervertebral disc cells in an alginate culture system}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {42}, Pages = {119 - 120}, Address = {Big Sky, MT, USA}, Year = {1999}, Keywords = {Cells;Cell culture;Mechanical properties;Synthesis (chemical);Morphology;Genes;Structure (composition);Growth kinetics;Mechanical testing;Statistical methods;}, Abstract = {The mechanical function of matrix synthesized by intervertebral disc (IVD) cells in alginate was examined by measuring material properties in both compression and shear testing of configurations. Samples were evaluated for mechanical function after 1, 4, 8, and 16 weeks in culture. The main results is that while IVD cells exhibit significant biosynthetic activity at both transcriptional and translational stages when cultured in alginate, they are not able to form a functional matrix.}, Key = {00275178035} } @article{00275178011, Author = {Setton, Lori A. and Perry, Charles H. and LeRoux, Michelle A. and Wang, Jean Y. and Howell, David S. and Cheung, Herman S.}, Title = {Altered mechanics of tibial cartilage following joint immobilization in a canine model}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {42}, Pages = {71 - 72}, Address = {Big Sky, MT, USA}, Year = {1999}, Keywords = {Cartilage;Joints (anatomy);Mathematical models;Biosynthesis;Enzymes;Collagen;}, Abstract = {To study the effect of immobilization, the compressive and shear properties of articular cartilage were quantified at sites corresponding to those of elevated MMP staining on the tibial plateau of mongrel dogs. Cartilage samples were tested in compression and torsion on a displacement-controlled rheometer. The samples were weighed after testing and again after lyophilization to determine water content as the percentage of tissue wet weight. The results support the hypothesis that knee joint immobilization will produce deleterious changes in cartilage function at the tibial plateau.}, Key = {00275178011} } @article{00275178144, Author = {Guilak, Farshid and Ting-Beall, H. Ping and Baer, Anthony E. and Erickson, Geoffrey R. and Jones, Wendy R. and Pearsall, Richard L. and Setton, Lori A.}, Title = {Identification of two biomechanically distinct cell populations in the intervertebral disc}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {42}, Pages = {337 - 338}, Address = {Big Sky, MT, USA}, Year = {1999}, Keywords = {Biomechanics;Bone;Cell culture;Proteins;Microscopic examination;Mathematical models;Regression analysis;}, Abstract = {A study was carried out to quantify the morphology and the viscoelastic mechanical properties of isolated cells from the anulus fibrosus (AF), transition zone (TZ), and nucleus pulposus (NP) and to examine the hypothesis that cellular properties may influence the biophysical environment of the cells. Pronounced differences were observed in the morphology of the NP cells as compared to the AF and TZ cells. Evidence was obtained concerning the existence of two biomechanically distinct cell populations in the intervertebral disc (IVD).}, Key = {00275178144} } @article{00275178590, Author = {Narmoneva, Daria A. and Wang, Jean Y. and Setton, Lori A.}, Title = {New method for determination of the tensile modulus of articular cartilage in situ in a free-swelling configuration}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {43}, Pages = {31 - 32}, Address = {Nashville, TN, USA}, Year = {1999}, Keywords = {Mechanical properties;Diseases;Swelling;Mechanical testing;Computer simulation;Numerical methods;Boundary conditions;Body fluids;Pressure;}, Abstract = {Using a triphasic mechanochemical theory, an attempt was made to quantify the material properties of canine and human cartilage studied in the free-swelling test and to compare them with site-matched values measured in uniaxial tensile testing. Values for the tensile modulus were found to compare well using the free-swelling and uniaxial testing methods. The results demonstrate the potential of this new methodology for quantifying cartilage properties in small cartilage samples.}, Key = {00275178590} } @article{00275178013, Author = {Elliott, Dawn M. and Setton, Lori A.}, Title = {Direct measurement of a complete set of orthotropic material properties for the human anulus fibrosus in tension}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {42}, Pages = {75 - 76}, Address = {Big Sky, MT, USA}, Year = {1999}, Keywords = {Neurology;Biochemical engineering;Swelling;Poisson ratio;Image analysis;}, Abstract = {In this study, an attempt was made to directly measure a complete set of Poisson's ratios and tensile moduli required for a description of the anulus fibrosus (AF) as an orthotropic material. Using a new method for surface strain measurement, it was demonstrated that the surface strain is nearly uniform under uniaxial tension for all orientations and all strain magnitudes. While the determined material coefficients form a complete set, the measured values did not correspond with the predicted relations between material coefficients for an orthotropic linear material.}, Key = {00275178013} } @article{00275178012, Author = {Setton, Lori A. and Perry, Charles H. and Elliott, Dawn M. and Wyland, Douglas J. and LeRoux, Michelle A. and Guilak, Farshid and Vail, Parker T.}, Title = {Anisotropic properties of the healing meniscus in tension}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {42}, Pages = {73 - 74}, Address = {Big Sky, MT, USA}, Year = {1999}, Keywords = {Musculoskeletal system;Blood vessels;Cells;Tissue;Mathematical models;Surgery;Poisson ratio;}, Abstract = {A study was carried out to quantify the anisotropic properties of the meniscus in tension. Skeletally-mature dogs underwent open surgery to create a meniscal tear in the right stifle joint. Tensile test samples were pre-equilibrated in 0.15M NaCl and width and thickness were measured. Samples were tested in uniaxial tension using a custom-built material test system. The resultant data provide evidence of highly anisotropic behaviors for the solid matrix of both the native and healing meniscal tissue.}, Key = {00275178012} } @article{6529438, Author = {Setton, L.A. and Baer, A.E. and Wang, J.Y. and Kraus, V.B.}, Title = {Biosynthesis of intervertebral disc matrix in vitro}, Journal = {Proceedings of the First Joint BMES/EMBS Conference. 1999 IEEE Engineering in Medicine and Biology 21st Annual Conference and the 1999 Annual Fall Meeting of the Biomedical Engineering Society (Cat. No.99CH37015)}, Volume = {vol.2}, Pages = {1325 vol.2 -}, Address = {Atlanta, GA, USA}, Year = {1999}, url = {http://dx.doi.org/10.1109/IEMBS.1999.804494}, Keywords = {bone;cellular biophysics;genetics;molecular biophysics;proteins;}, Abstract = {Cells of the intervertebral disc are shown to express genes for aggrecan and collagen in an in vitro alginate culture system. Despite evidence for significant biosynthesis, the cells appear unable to assemble a mechanically functional matrix in this in vitro system}, Key = {6529438} } @article{99094779171, Author = {LeRoux, Michelle A. and Guilak, Farshid and Setton, Lori A.}, Title = {Compressive and shear properties of alginate gel: Effects of sodium ions and alginate concentration}, Journal = {Journal of Biomedical Materials Research}, Volume = {47}, Number = {1}, Pages = {46 - 53}, Year = {1999}, url = {http://dx.doi.org/10.1002/(SICI)1097-4636(199910)47:1<46::AID-JBM6>3.0.CO;2-N}, Keywords = {Hydrogels;Biopolymers;Tissue culture;Sodium chloride;Physiology;Compression testing;Stress relaxation;Elastic moduli;Composition effects;Stress analysis;Stiffness;Calcium compounds;}, Abstract = {The equilibrium and viscoelastic properties of alginate gel crosslinked with Ca<sup>2+</sup> were determined as a function of alginate concentration and duration of exposure to physiologic concentrations of NaCl. Compressive and shear stress relaxation tests and oscillatory shear tests were performed to measure the material properties at two time periods after storage in NaCl compared to no NaCl exposure. The effect of concentration was determined by testing 1-3% alginate gel in a bath of physiological NaCl and CaCl<sub>2</sub>. After 15 h of exposure to NaCl, the compressive, equilibrium shear, and dynamic shear moduli decreased by 63, 84, and 90% of control values, respectively. The material properties exhibited no further changes after 7 days of exposure to NaCl. The loss angle and amplitude of the relaxation function in the shear also decreased, indicating less viscous behaviors in both dynamic and transient configurations. All moduli, but not the loss angle, significantly increased with increasing alginate concentration. The observed decrease in compressive and shear stiffness for alginate gel after exposure to Na<sup>+</sup> was significant and indicated that physiological conditions will soften the gel over a time period of up to 7 days after gelation. The alginate gel retains significant solidlike behaviors, however, as measured by a loss angle of approximately 3°. This study provides the first available data for material properties of alginate gel tested in physiological saline.}, Key = {99094779171} } @article{99094778983, Author = {Elliott, Dawn M. and Guilak, Farshid and Vail, T. Parker and Wang, Jean Y. and Setton, Lori A.}, Title = {Tensile properties of articular cartilage are altered by meniscectomy in a canine model of osteoarthritis}, Journal = {Journal of Orthopaedic Research}, Volume = {17}, Number = {4}, Pages = {503 - 508}, Year = {1999}, Keywords = {Tensile properties;Joints (anatomy);Physiological models;Biomechanics;Elastic moduli;Stress relaxation;Morphology;Tensile testing;Surgery;}, Abstract = {Loss of or damage to the meniscus alters the pattern of loading in the knee joint and frequent leads to cartilage degeneration and osteoarthritis. The mechanical properties of articular cartilage have been shown to reflect the extent of cartilage degeneration in human osteoarthritis and in experimental models of joint disease, but there is little experimental data documenting changes in cartilage mechanics following meniscectomy. We hypothesized that the tensile properties of the surface zone of articular cartilage are altered following total medial meniscectomy. Twelve mongrel dogs underwent complete resection of the medial meniscus in the right knee, and the femoral cartilage was studied 12 weeks after the operation. We performed uniaxial, tensile stress-relaxation tests to determine the equilibrium tensile modulus of surface-zone cartilage. Water and glycosaminoglycan content were also measured at site-matched locations. The tensile moduli of the cartilage decreased significantly following meniscectomy. The linear region modulus decrease by 40%, from 25.5±7.7 to 15.3±7.2 MPa. There was a weak (r = -0.45), but significant, correlation between the linear region modulus and the gross morphological grade for cartilage damage. Water and glycosaminoglycan content did not change following meniscectomy. Composition was not correlated with mechanic properties or morphological grade, suggesting that cartilage structure may play a more important role than composition in determining the mechanical properties. The observed decrease in cartilage material properties provides a quantitative measure of the loss of cartilage function following meniscectomy and reflects a pattern of change that is consistent with damage to the collagen-proteoglycan solid network.}, Key = {99094778983} } @article{6279880, Author = {Hsu, E.W. and Setton, L.A.}, Title = {Diffusion tensor microscopy of the intervertebral disc anulus fibrosus}, Journal = {Magn. Reson. Med. (USA)}, Volume = {41}, Number = {5}, Pages = {992 - 9}, Year = {1999}, url = {http://dx.doi.org/10.1002/(SICI)1522-2594(199905)41:5<992::AID-MRM19>3.0.CO;2-Y}, Keywords = {biodiffusion;biomedical MRI;microscopy;tensors;}, Abstract = {Morphologically accurate biomechanical models of the intervertebral disc anulus fibrosus (AF) require precise knowledge of its lamellar architecture; however, available methods of assessment are limited by poor spatial resolution or the destructive nature of the technique. In a novel approach, diffusion tensor microscopy was used in this study to characterize the microstructure of excised porcine AF samples. Results show diffusion in the AF to be anisotropic. The orientations of anisotropy exhibit a layered morphology that agrees with light micrographs of the corresponding samples, and the behavior of the orientation angles is consistent with the known AF collagen fiber architecture. A static magnetic field-dependent relaxation anisotropy was observed in the AF, which has methodological implications for magnetic resonance (MR) imaging of ordered collageneous tissues. These findings present MR diffusion tensor microscopy as a potentially valuable tool to assess quantitatively and nondestructively water diffusion anisotropy and lamellar structure of the intervertebral disc AF}, Key = {6279880} } @article{6230291, Author = {Narmoneva, D.A. and Wang, J.Y. and Setton, L.A.}, Title = {Nonuniform swelling-induced residual strains in articular cartilage}, Journal = {J. Biomech. (UK)}, Volume = {32}, Number = {4}, Pages = {401 - 8}, Year = {1999}, url = {http://dx.doi.org/10.1016/S0021-9290(98)00184-5}, Keywords = {biological tissues;biomechanics;osmosis;swelling;}, Abstract = {Swelling effects in cartilage originate from an interstitial osmotic pressure generated by the presence of negatively charged proteoglycans in the tissue. This swelling pressure gives rise to a non-zero residual strain in the cartilage solid matrix in the absence of externally applied loads. Previous studies have quantified swelling effects in cartilage as volumetric or dimensional change of excised samples in varying osmotically active solutions. This study presents a new optical technique for measuring two-dimensional swelling-induced residual strain fields in planar samples of articular cartilage attached to the bone (i.e., in situ). Osmotic loading was applied to canine cartilage-bone samples by equilibration in external baths of varying NaCl concentration. Non-zero swelling-induced strains were measured in physiological saline, giving evidence of the existence of residual strains in articular cartilage. Only one component of planar strain (i.e., in thickness direction) was found to be non-zero. This strain was found to be highly non-uniform in the thickness direction, with evidence of compressive strain in the deep zone of cartilage and tensile strain in the middle and surface zones. The obtained results can be used to characterize the material properties of the articular cartilage solid matrix, with estimated values of 26 MPa for the tensile modulus for middle zone cartilage. The method provides the basis to obtain material properties of the cartilage solid matrix from a simple, free-swelling test and may be useful for quantifying changes in cartilage properties with injury, degeneration and repair}, Key = {6230291} } @article{6058555, Author = {Iatridis, J.C. and Setton, L.A. and Foster, R.J. and Rawlins, B.A. and Weidenbaum, M. and Mow, V.C.}, Title = {Degeneration affects the anisotropic and nonlinear behaviors of human anulus fibrosus in compression}, Journal = {J. Biomech. (UK)}, Volume = {31}, Number = {6}, Pages = {535 - 44}, Year = {1998}, url = {http://dx.doi.org/10.1016/S0021-9290(98)00046-3}, Keywords = {biomechanics;elastic moduli;permeability;stress relaxation;swelling;}, Abstract = {Axial and radial specimens of non-degenerate and degenerate human anulus fibrosus (AF) were tested in confined compression to test the hypothesis that degeneration significantly affects the compressive properties of AF. Due to the highly oriented structure of AF, a secondary objective was to investigate anisotropic behaviors of AF in compression. Uniaxial swelling and stress-relaxation experiments were performed on site-matched samples of anulus from the anterior outer region of L2-3 intervertebral discs. The experimental stress-relaxation behavior was modeled using the finite deformation biphasic theory and a finite-difference approximation scheme. Significant effects of degeneration but not orientation were detected for the reference stress offset, σ<sub>offset</sub>, and parameters describing the compressive stiffness (i.e., reference aggregate modulus, H<sub>A0</sub>, and nonlinear stiffening coefficient, β). Average values were 0.13±0.06 and 0.05±0.05 MPa for σ<sub>offset</sub>, 0.56±0.21 and 1.10±0.53 MPa for H<sub>A0</sub> and 2.13±1.48 and 0.44±0.61 for β for all normal and degenerate specimens, respectively. No significant effect of degeneration or orientation were detected for either of the parameters describing the strain-dependent permeability (i.e. reference permeability, k<sub>0</sub>, and strain-dependent permeability coefficient M) with average values for all specimens of 0.20±0.10×10<sup>-15</sup> m<sup>4</sup>/N-s and 1.18±1.30 for k<sub>0</sub> and M, respectively. The loss of σ<sub>offset</sub> was compensated with an elastic stiffening and change in the shape of the equilibrium stress-strain curve with H<sub>A0</sub> for degenerate tissues almost twice that of normal tissues and β less than one sixth. The increase in reference elastic modulus with degeneration is likely related to an increase in tissue density resulting from the loss of water content. The significant effects of degeneration reported in this study suggested a shift in load carriage from fluid pressurization and swelling pressure to deformation of the solid matrix of the AF. The results also suggest that the highly organized and layered network of the anulus fibrosus, which gives rise to significant anisotropic effects in tension, does not play a major role in contributing to the magnitude of compressive stiffness or the mechanisms of fluid flow of the anulus in the confined compression configuration}, Key = {6058555} } @article{6004116, Author = {Setton, L.A. and Tohyama, H. and Mow, V.C.}, Title = {Swelling and curling behaviors of articular cartilage}, Journal = {Trans. ASME, J. Biomech. Eng. (USA)}, Volume = {120}, Number = {3}, Pages = {355 - 61}, Year = {1998}, Keywords = {biomechanics;swelling;}, Abstract = {A new experimental method was developed to quantify parameters of swelling-induced shape change in articular cartilage. Full-thickness strips of cartilage were studied in free-swelling tests and the swelling-induced stretch, curvature, and areal change were measured. In general, swelling-induced stretch and curvature were found to increase in cartilage with decreasing ion concentration, reflecting an increasing tendency to swell and “curl” at higher swelling pressures. An exception was observed at the articular surface, which was inextensible for all ionic conditions. The swelling induced residual strain at physiological ionic conditions was estimated from the swelling-induced stretch and found to be tensile and from 3-15 percent. Parameters of swelling were found to vary with sample orientation, reflecting a role for matrix anisotropy in controlling the swelling-induced residual strains. In addition, the surface zone was found to be a structurally important element, which greatly limits swelling of the entire cartilage layer. The findings of this study provide the first quantitative measures of swelling-induced residual strain in cartilage ex situ, and may be readily adapted to studies of cartilage swelling in situ}, Key = {6004116} } @article{5777661, Author = {Iatridis, J.C. and Setton, L.A. and Weidenbaum, M. and Mow, V.C.}, Title = {The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear}, Journal = {J. Biomech. (UK)}, Volume = {30}, Number = {10}, Pages = {1005 - 13}, Year = {1997}, url = {http://dx.doi.org/10.1016/S0021-9290(97)00069-9}, Keywords = {biomechanics;biorheology;bone;stress relaxation;viscoelasticity;}, Abstract = {The viscoelastic behavior of the nucleus pulposus was determined in shear under transient and dynamic conditions and was modeled using a linear viscoelastic model with a variable amplitude relaxation spectrum. During stress-relaxation tests, the shear stress of the nucleus pulposus relaxed nearly to zero indicative of the fluid nature of the tissue. Under dynamic conditions, however, the nucleus pulposus exhibited predominantly `solid-like' behavior with values for dynamic modulus (|G*|) ranging from 7 to 20 kPa and loss angle (δ) ranging from 23 to 30° over the range of angular frequencies tested (1-100 rad s<sup>-1</sup>). This frequency-sensitive viscoelastic behavior is likely to be related to the highly polydisperse populations of nucleus pulposus molecular constituents. The stress-relaxation behavior, which was not linear on a semi-log plot (in the range τ<sub>1</sub>≪t≪τ<sub>2</sub>), required a variable amplitude relaxation spectrum capable of describing this frequency sensitive behavior. The stress-relaxation behavior was well described by this linear viscoelastic model with variable amplitude relaxation spectrum; however, the dynamic moduli were underpredicted by the model which may be related to non-linearities in the material behavior}, Key = {5777661} } @article{98054187915, Author = {Narmoneva, D.A. and Wang, J.Y. and Patel, S.S. and Howell, D.S. and Setton, L.A.}, Title = {Altered swelling-induced strain fields in articular cartilage following periods of immobilization}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {36}, Pages = {125 - 126}, Address = {Dallas, TX, USA}, Year = {1997}, Keywords = {Cartilage;Swelling;Volume fraction;Strain;Statistical tests;}, Abstract = {An experimental technique was developed for measuring the swelling-induced strains in articular cartilage while attached to the subchondral bone, a configuration more representative of the in vivo state than excised cartilage. The cartilage attachment to the bone greatly limits the free swelling effect in which the strains observed were much smaller than those for excised tissue samples. The components of swelling strain varies from compressive at the deep zone to tensile at the middle-surface zones. Periods of immobilization produced an increase in strains which was not related to a change in either water volume fraction or fixed charge density.}, Key = {98054187915} } @article{97063692025, Author = {Iatridis, James C. and Setton, Lori A. and Weidenbaum, Mark and Mow, Van C.}, Title = {Alterations in the mechanical behavior of the human lumbar nucleus pulposus with degeneration and aging}, Journal = {Journal of Orthopaedic Research}, Volume = {15}, Number = {2}, Pages = {318 - 322}, Year = {1997}, Keywords = {Musculoskeletal system;Biomechanics;Morphology;Composition;}, Abstract = {This study tested the hypothesis that changes in the morphology and composition of the nucleus pulposus with age and degeneration have associated changes in its mechanical properties. A torsional shear experiment was used to determine viscoelastic shear properties of cylindrical samples of human nucleus pulposus with large ranges of grades of morphological degeneration (normal to severely degenerated) and ages (range: 16-88 years; average: 57 ± 21.5 years). Viscoelastic shear properties were determined from stress-relaxation and dynamic sinusoidal tests. A linear viscoelastic law with a variable-amplitude relaxation spectrum was used to model experimental behaviors of nucleus pulposus specimens. A statistically significant increase in the instantaneous and dynamic shear moduli was found with increasing age and grade of degeneration; the values for moduli ranged from 5.0 to 60 kPa. A significant decrease in tanδ was also detected; the values ranged from 0.43 to 0.33, indicating a decreased capacity for the nucleus pulposus to dissipate energy. The dynamic modulus and tanδ were also significantly affected by frequency. It was generally concluded that the nucleus pulposus undergoes a transition from 'fluid-like' behavior to more 'solid-like' behavior with aging and degeneration.}, Key = {97063692025} } @article{98054187935, Author = {Elliott, Dawn M. and LeRoux, Michelle A. and Laursen, Tod A. and Setton, Lori A.}, Title = {Formulation of a continuum anisotropic model for the anulus fibrosus in tension}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {36}, Pages = {165 - 166}, Address = {Dallas, TX, USA}, Year = {1997}, Keywords = {Tissue;Anisotropy;Aspect ratio;Strain;Stresses;Mathematical models;Finite element method;Elastic moduli;}, Abstract = {The anulus fibrosus (AF) of the intervertebral disc is a highly structured material made up of alternating tissue layers with collagen fibers oriented +30° and -30° to the circumferential axis. Special organization of the AF gives rise to strongly anisotropic behaviors which may contribute to its mechanical function. A continuum formulation for the AF as a linear orthotropic material with a complete set of material properties is proposed. Finite element implementation of the model is also developed to further compare model predictions with experimental findings for the AF in tension.}, Key = {98054187935} } @article{97023540093, Author = {Elliott, Dawn M. and Setton, Lori A. and Shah, Maulin P. and Vail, T. Parker and Guilak, Farshid}, Title = {Effects of meniscectomy on the tensile properties of articular cartilage}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {33}, Pages = {247 - 248}, Address = {Atlanta, GA, USA}, Year = {1996}, Keywords = {Cartilage;Tensile properties;Surgery;Joints (anatomy);Biomedical engineering;Models;Stiffness;Proteins;Collagen;Composition;Biosynthesis;Hydration;}, Abstract = {A study was conducted to quantify the tensile properties of articular cartilage in an experimental model of meniscectomy. The meniscus was completely resected in the right knees of 4 skeletally mature mongrel dogs. The left knee was used as an unoperated control. Animals were sacrificed 12 weeks after surgery and both legs stored at -20°C until testing. Successive tensile stress-relaxation tests were performed using a screw driven uniaxial testing system. All tests were performed in a 0.15M NaCl bath at room temperature. The findings were then compared with those of both human osteoarthritis (OA) and experimental models of joint instability.}, Key = {97023540093} } @article{95092853089, Author = {Setton, Lori A. and Mow, Van C.}, Title = {Contributions of flow-dependent and flow-independent viscoelasticity to the behavior of articular cartilage in oscillatory compression}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {29}, Pages = {307 - 308}, Address = {Beever Creek, CO, USA}, Year = {1995}, Keywords = {Cartilage;Viscoelasticity;Oscillations;Mathematical models;Tensors;Strain;Relaxation processes;Deformation;Mechanical permeability;Stresses;Hysteresis;}, Abstract = {While flow-dependent viscoelasticity can explain much of the observed dependence of cellular response to amplitude and frequency of loading, as well as spatial position in the explant, contributions of the flow-independent viscoelastic mechanism may also be considered to be significant, particularly in tissues with large values of hydraulic permeability. In this study, a model incorporating both flow-dependent and flow-independent viscoelastic mechanisms, the biphasic poroviscoelastic theory, is used to predict the mechanical environment of the extracellular matrix within a cartilage explant in response to a forced oscillatory displacement.}, Key = {95092853089} } @article{95102886799, Author = {Setton, L.A. and Mow, V.C. and Howell, D.S.}, Title = {Mechanical behavior of articular cartilage in shear is altered by transection of the anterior cruciate ligament}, Journal = {Journal of Orthopaedic Research}, Volume = {13}, Number = {4}, Pages = {473 -}, Year = {1995}, Key = {95102886799} } @article{95092853061, Author = {Iatridis, James C. and Setton, Lori A. and Foster, Robert J. and Rawlins, Bernard A. and Weidenbaum, Mark and Mow, Van C.}, Title = {Human anulus fibrosus behaves nonlinearly and isotropically in finite deformation confined compression}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {29}, Pages = {251 - 252}, Address = {Beever Creek, CO, USA}, Year = {1995}, Keywords = {Biomechanics;Compressive strength;Deformation;Anisotropy;Compression testing;Stresses;Relaxation processes;Curve fitting;Calculations;Strain;Mathematical models;Pressure effects;}, Abstract = {Human anulus fibrosus (AF) of the intervertebral disk exhibits nonlinear and anisotropic behavior in tension. This paper investigates both anisotropic and nonlinear behaviors of the AF in the confined compression testing configuration under conditions of finite deformation. The finite deformation formulation of the biphasic theory is used to described the experimental stress-relaxation behavior of AF under conditions of large deformation. In this formulation, the equilibrium elastic behavior is described by two material parameters: the aggregate modulus at zero strain (H<sub>Ao</sub>) and the nonlinear stiffening coefficient (β).}, Key = {95092853061} } @article{95012532254, Author = {Setton, L.A. and Tohyama, H. and Lai, W.M. and Guilak, F. and Mow, V.C.}, Title = {Experimental measurement of the in vitro curling behavior of articular cartilage}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {28}, Pages = {135 - 136}, Address = {Chicago, IL, USA}, Year = {1994}, Keywords = {Swelling;Residual stresses;Strain;Image analysis;Computer aided analysis;Measurement errors;Sodium chloride;Polynomials;Least squares approximations;Mathematical models;Collagen;}, Abstract = {The objective of this study was to develop a non-contacting optical method to quantify the shape changes in cartilage in vitro, as a first step toward determining a potential mechanical role for the swelling-induced residual stresses and strain in cartilage in situ. Rectangular strips of articular cartilage prepared from the lateral facet of skeletally-mature bovine patella were placed in a glass dish and allowed to equilibrate in NaCl solution. A calibration cylinder was affixed within each glass dish. Both the cylinder and the strips were photographed. The images were analyzed for dimensional changes. All the samples demonstrated the characteristic curling and swelling behaviors after removal from the subchondral bone, and in response to changes in the concentration of the external bath.}, Key = {95012532254} } @article{95012532345, Author = {Iatridis, James C. and Setton, Lori A. and Weidenbaum, Mark and Mow, Van C.}, Title = {Determination of a relaxation spectrum to evaluate the viscoelastic behavior of the nucleus pulposus in shear}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {28}, Pages = {317 - 318}, Address = {Chicago, IL, USA}, Year = {1994}, Keywords = {Cartilage;Pressurization;Viscoelasticity;Stress relaxation;Spectrometers;Shear stress;Torque;Mathematical models;Integral equations;}, Abstract = {This study was designed to determine the intrinsic viscoelastic behaviour of NP in torsional shear, and to obtain a relaxation spectrum capable of describing this behaviour. Several relaxation functions based on both discrete and continuous relaxation spectra were investigated to describe the intrinsic viscoelastic effects for the NP. It was observed that the shear behavior of the NP exhibits pronounced viscoelastic effects, as demonstrated by a considerable stress-relaxation effect.}, Key = {95012532345} } @article{94091407745, Author = {Mueller, F.J. and Setton, L.A. and Manicourt, D.H. and Mow, V.C. and Howell, D.S. and Pita, J.C.}, Title = {Centrifugal and biochemical comparison of proteoglycan aggregates from articular cartilage in experimental joint disuse and joint instability}, Journal = {Journal of Orthopaedic Research}, Volume = {12}, Number = {4}, Pages = {498 - 508}, Year = {1994}, Keywords = {Biological materials;Biochemistry;Joints (anatomy);Models;Orthopedics;}, Abstract = {Two models involving altered joint loading were compared with regard to their effects on the biochemical composition and proteoglycan aggregate structure of articular cartilage. Disuse atrophy was created in greyhound dogs by nonrigid immobilization of the right knee in 90° of flexion, and joint instability was created by transection of the anterior cruciate ligament. Similarities and differences between the two experimental groups at two different time periods were examined to investigate why joint instability induces progressive and irreversible changes to the articular cartilage, whereas joint disuse induces changes that may be reversible when the joint is remobilized. The following studies were performed on the cartilage from all experimental and control groups: (a) compositional analyses to determine water, uronate, and hydroxyproline contents; (b) high performance liquid chromatography for detection of hyaluronan and chondroitin sulfates; and (c) centrifuguration analyses of nondissociatively extracted and purified proteoglycans to isolate and quantify the populations of monomers and slow and fast-sedimenting families of aggregates. In general, all cartilage was found to have a decreased ratio of proteoglycan to collagen after 4 weeks of disuse, and this ratio returned to control values at 8 weeks. In contrast, cartilage had an elevated ratio of proteoglycan to collagen as well as increased hydration at 12 weeks after transection of the anterior cruciate ligament. The most striking contrast between the two models was the finding of an approximately 80% decrease in the content of hyaluronan at both time periods after transection of the anterior cruciate ligament, with no evidence of a change after disuse. The results of centrifugation analyses indicated a significant decrease in the quantity of proteoglycan aggregates in both models.}, Key = {94091407745} } @article{94091407741, Author = {Setton, L.A. and Mow, V.C. and Muller, F.J. and Pita, J.C. and Howell, D.S.}, Title = {Mechanical properties of canine articular cartilage are significantly altered following transection of the anterior cruciate ligament}, Journal = {Journal of Orthopaedic Research}, Volume = {12}, Number = {4}, Pages = {451 - 463}, Year = {1994}, Keywords = {Mechanical properties;Ligaments;Network protocols;Orthopedics;Biomedical engineering;}, Abstract = {The compressive, tensile, and swelling properties of articular cartilage were studied at two time periods following transection of the anterior cruciate ligament in the knee of greyhound dogs. An experimental protocol was designed to quantify the essential equilibrium and biphasic material properties of cartilage in tension compression and shear, as well as the parameters of isometric swelling behavior. All properties were measured at several sites to elicit differences between sites of frequent and less frequent contact. Hydration was determined at each site and was compared with the material properties of cartilage from corresponding sites. There were extensive changes in all compressive, tensile, and swelling properties of cartilage after transection of the anterior cruciate ligament. Twelve weeks after surgery, the intrinsic moduli were reduced significantly in compression (approximately 24 % of control values), tension (approximately 64%), and shear (approximately 24 %), and the hydraulic was elevated significantly (approximately 48 %). Significant-increases in hydration (approximately 9 %) also were observed, as well as a strong correlation of hydration with hydraulic permeability. The pattern of these changes was not found to differ with site in the joint, but significant differences were observed in the magnitude of change for cartilage from the femoral groove and the femoral condyle. The pattern and extent of changes in the material properties following transection of the anterior cruciate ligament indicate that altered loading of the joint severely compromises the overall mechanical behavior of articular cartilage. The observed loss of matrix stiffness in compression, tension, and shear is associated with increase in the deformation of the solid matrix, a diminished ability to resit swelling, and the increase in hydration observed in this study.}, Key = {94091407741} } @article{93061004853, Author = {Setton, Lori A. and Zhu, Wenbo and Weidenbaum, Mark and Ratcliffe, Anthony and Mow, Van C.}, Title = {Compressive properties of the cartilaginous end-plate of the baboon lumbar spine}, Journal = {Journal of Orthopaedic Research}, Volume = {11}, Number = {2}, Pages = {228 - 239}, Year = {1993}, Keywords = {Cartilage;Body fluids;Viscoelasticity;Compressibility of liquids;Compression testing;Flow of fluids;Mechanical properties;Composition;Mathematical models;Curve fitting;}, Abstract = {The viscoelastic behavior of the cartilaginous end-plate of the baboon (Papio anubis) was studied in an experiment on compressive creep. Data were analyzed with the biphasic poroviscoelastic constitutive theory to assess the relative contributions of flow-dependent and flow-independent viscoelastic mechanisms to the observed creep behavior. Material coefficients describing the equilibrium compressive behavior (H<sub>A</sub>) and both flow-independent (c, τ<sub>1</sub>, and τ<sub>2</sub>) and flow-dependent (k) viscoelastic effects were determined for the end-plate by the curve-fitting of the theoretical solution to the experimental creep data. Biochemical analyses were performed to test for potential relationships between material properties and composition which may give rise to the viscoelastic behavior of the end-plate. The results indicate that the cartilaginous end-plate has a hydraulic permeability of 14.3×10<sup>-14</sup> m<sup>4</sup>/N-s, which is associated with rapid transport and pressurization of the interstitial fluid in response to loading and an increased emphasis on flow-independent viscoelastic effects. Biochemical analyses for water, sulfated glycosaminoglycan content, and hydroxyproline indicate that the end-plate of the baboon is compositionally similar to the cartilaginous end-plate in humans. Interpretation of the mechanical and compositional data suggests that fluid pressurization in the cartilaginous end-plate may be important in the maintenance of a uniform stress distribution across the boundary between vertebral body and intervertebral disc.}, Key = {93061004853} } @article{94031231322, Author = {Setton, L.A. and Lai, W.M. and Mow, V.C.}, Title = {Swelling-induced residual stress and the mechanism of curling in articular cartilage in vitro}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {26}, Pages = {59 - 62}, Address = {New Orleans, LA, USA}, Year = {1993}, Keywords = {Residual stresses;Swelling;Mathematical models;Physical properties;Biomedical engineering;Biological materials;}, Abstract = {The triphasic theory has been used to analyze the in vitro free-swelling behavior of two-dimensional strips of articular cartilage with an inhomogeneous distribution of negative fixed charge density. The results indicate that the model can predict the characteristic curling behavior of cartilage strips. The free swelling geometry demonstrated a dependence on aspect ratio of the strip length thickness, so that the curling or cartilage strips increased with decreasing cartilage thickness. It was concluded that a physiological variation in fixed charge density gives rise to a non-uniform distribution of residual stress and strain, and is thus responsible for the curling of excised samples in vitro. The mathematical solution presented in this study provides a means for calculating the residual strains, stresses and swelling pressures in the equilibrium free-swelling configuration and may prove useful in the development of an experimental protocol for measurement of the residual strains in vitro and in situ.}, Key = {94031231322} } @article{4410101, Author = {Setton, L.A. and Zhu, W. and Mow, V.C.}, Title = {The biphasic poroviscoelastic behavior of articular cartilage: role of the surface zone in governing the compressive behavior}, Journal = {J. Biomech. (UK)}, Volume = {26}, Number = {4-5}, Pages = {581 - 92}, Year = {1993}, Keywords = {biorheology;creep;viscoelasticity;}, Abstract = {To assess the influence of the surface zone on the viscoelastic properties of cartilage under compressive loading, the authors prepared osteochondral plugs from skeletally mature steers, with and without the surface zone of articular cartilage, for study in the confined compression creep experiment. The relative contributions of two viscoelastic mechanisms, i.e. a flow-independent mechanism (Hayes and Bodine, ibid., vol.11, p407-19, 1978), and a flow-dependent mechanism (Mow et al., J. Biomech. Engng. ibid., vol.102, p.73-84, 1980), to the compressive creep response of these two types of specimens were determined using the biphasic poroviscoelastic theory proposed by (Mak., ibid., vol.20, p.703-14, 1986). From the experimental results and the biphasic poroviscoelastic theory, the authors found that frictional drag associated with interstitial fluid flow and fluid pressurization are the dominant mechanisms of load support in the intact specimens, i.e. the flow-dependent mechanisms alone with sufficient to describe normal articular cartilage compressive creep behavior. For specimens with the surface removed, the authors found an increased creep rate which was derived from an increased tissue permeability, as well as significant changes in the flow-independent parameters of the viscoelastic solid matrix}, Key = {4410101} } @article{93020709999, Author = {Setton, L.A. and Gu, W.Y. and Lai, W.M. and Mow, V.C.}, Title = {Pre-stress in articular cartilage due to internal swelling pressure}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {22}, Pages = {485 - 488}, Address = {Anaheim, CA, USA}, Year = {1992}, Keywords = {Stress analysis;Elasticity;Dynamic loads;Structural analysis;Pressure effects;Mathematical models;}, Abstract = {The triphasic theory has been used to calculate the pre-stress in spherical and cylindrical layer models of articular cartilage. In the present study, cartilage was assumed to be homogeneous with a uniform fixed charge density. The tissue is attached to subchondral bone of a given radius of curvature. It has been determined that: 1) the maximum radial elastic stress occurs at the cartilage-bone junction and the maximum circumferential elastic stress occurs at the cartilage surface; 2) radial elastic stress is generally larger than the tangential elastic stress; 3) the maximum elastic stress increases with decreasing radius of curvature for cartilage layers of fixed thickness. The existence of pre-stresses may serve to reduce collagen tension resulting from joint loading, and may also be an important factor in determining the collagen ultrastructure within the cartilage solid matrix.}, Key = {93020709999} } @article{93020710026, Author = {Setton, L.A. and Mow, V.C.}, Title = {Generalized biphasic poroviscoelastic model for articular cartilage: Theory and experiments}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {22}, Pages = {589 - 592}, Address = {Anaheim, CA, USA}, Year = {1992}, Keywords = {Viscoelasticity;Porosity;Strength of materials;Shear stress;Deformation;Anelastic relaxation;Loads (forces);Mechanical testing;Joints (anatomy);Mathematical models;}, Abstract = {The shear and bulk deformation viscoelastic spectrums of the solid matrix of articular cartilage has been determined using the biphasic poroviscoelastic theory in combination with data from two independent stress-relaxation experiments in compression and pure shear. The results show that viscoelasticity of the solid matrix in bulk deformation exerts a strong influence on the compressive behavior of cartilage for short times after rapid loading. For long time periods, shear and bulk viscoelasticity contribute almost equally to the deformational response of the tissue. Results indicate that the model for studying cartilage behavior should reflect the particular time scales and configuration of the specific test. The method presented in this study should allow investigators to choose the appropriate biphasic model to represent cartilage deformational behavior in studying diarthrodial joint biomechanics.}, Key = {93020710026} } @article{93020704622, Author = {Lai, W. Michael and Gu, Weiyong and Setton, Lori A. and Mow, Van C.}, Title = {Conditional equivalence of chemical loading and mechanical loading on articular cartilage}, Journal = {American Society of Mechanical Engineers, Bioengineering Division (Publication) BED}, Volume = {20}, Pages = {481 - 484}, Address = {Atlanta, GA, USA}, Year = {1991}, Keywords = {Stresses;Chemical reactions;Sodium chloride;Solutions;Joints (anatomy);}, Abstract = {The objective of this paper is to ascertain the conditions for equivalence between chemical or osmotic loading and mechanical loading on articular cartilage. Constitutive equations for a charged-hydrated-soft tissue are given and chemical potentials are derived. Equivalence between chemical vs. mechanical load is discussed. Using the triphasic constitutive equations, it is shown that for every chemical load generated by a given concentration of polyethylene glycol (PEG) in a NaCl solution there corresponds an isotropic mechanical load, P<sub>A</sub>, which imparts to the tissue an identical equilibrium deformation. However, the mechanical load must be delivered in an isotropic manner via rigid-porous, free-draining loading platens.}, Key = {93020704622} } @article{7435933, Author = {Flahiff, C.M. and Narmoneva, D.A. and Huebner, J.L. and Kraus, V.B. and Guilak, F. and Setton, L.A.}, Title = {Osmotic loading to determine the intrinsic material properties of guinea pig knee cartilage}, Journal = {J. Biomech. (UK)}, Volume = {35}, Number = {9}, Pages = {1285 - 90}, url = {http://dx.doi.org/10.1016/S0021-9290(02)00079-9}, Keywords = {biochemistry;biological techniques;biological tissues;biomechanics;elastic moduli;fluorescence;optical microscopy;osmosis;swelling;}, Abstract = {Few methods exist to study cartilage mechanics in small animal joints due to the difficulties associated with handling small tissue samples. In this study, we apply an osmotic loading method to quantify the intrinsic material properties of articular cartilage in small animal joints. Cartilage samples were studied from the femoral condyle and tibial plateau of two-month old guinea pigs. Swelling strains were measured using confocal fluorescence scanning microscopy in samples subjected to osmotic loading. A histochemical staining method was developed and calibrated for quantification of negative fixed charge density in guinea pig cartilage. Site-matched swelling strain data and fixed charge density values were then used with a triphasic theoretical model for cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. Moduli obtained in this study (7.2 MPa femoral condyle; 10.8 MPa, tibial plateau) compare well with previously reported values for the tensile moduli of human and other animal cartilages determined from uniaxial tension experiments. This study provides the first available data for material properties and fixed charge density in cartilage from the guinea pig knee and suggests a promising method for tracking changes in cartilage mechanics in small animal models of degeneration}, Key = {7435933} } | |
Duke University * Pratt * CBTE * Reload * Login |