Material Constants for Human Annulus Fibrosus Depend on Water Content and Reference Configuration

We apply a special theory of an incompressible mixture of an elastic solid and an inviscid fluid (Klisch and Lotz, 1998) to experimental data for healthy human annulus fibrosus tested in a stress-relaxation confined compression protocol. The material constants revealed no significant differences due to orientation (i.e., axial vs. radial, n = 16). The aggregate modulus and initial permeability constants were significantly different (n = 32) due to the choice of theory used to fit the data (i.e., that of Klisch and Lotz (1998) vs. that of Holmes and Mow (1990)) and were significantly correlated with initial water content.