The primary objective of this thesis was to develop a better understanding of cartilage mechanics by revealing the material properties of the tissue to yet another level of complexity. The inhomogeneities of articular cartilage were investigated by determining the depth-dependent compressive Young’s modulus, Poisson’s ratio, intrinsic solid matrix stiffness and fixed charge density. The anisotropy of the tissue was discussed by focusing on the measurement of equilibrium compressive elastic properties along its three characteristic directions in order to determine material symmetry o f cartilage in compression. Tension-compression nonlinearity was explored through the strain-softening behavior of cartilage that has been observed in common compression tests. A triphasic conewise nonlinear elasticity model was proposed to interpret the strain-softening in the context of tension-compression nonlinearity and osmotic swelling. The mechano-electrochemical responses of the tissue were addressed by incorporating the depth-dependent material properties into the triphasic mixture model to describe the environment of chondrocytes.

Prior to these efforts, a methodology for measuring the deformation fields was developed and validated for its application to cartilage experimental mechanics. This methodology combines the common cartilage testing configurations with digital video microscopy, optimized digital image correlation, thin-plate smoothing spline and generalized cross-validation to achieve the desired efficiency and accuracy. This methodology formed the technique basis for all the experimental work in this thesis.

Finally, the implications of the complexity of tissue properties on chondrocyte environment were explored by incorporating the experimental measurements of the tissue inhomogeneities into rigorous theoretical modeling (e.g., the biphasic or triphasic mixture theory), representing an initial effort towards the understanding of mechanotransduction of chondrocytes.