- Iatridis, J.C. and Setton, L.A. and Weidenbaum, M. and Mow, V.C., The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear,
J. Biomech. (UK), vol. 30 no. 10
pp. 1005 - 13 [S0021-9290(97)00069-9] .
(last updated on 2007/04/10)
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-1). 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 τ1≪t≪τ2), 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