A BIMODULAR SECOND-ORDER ORTHOTROPIC STRESS CONSTITUTIVE EQUATION FOR CARTILAGE

摘要

The design of tissue-engineered constructs grown in vitro is a promising treatment strategy for degenerated cartilaginous tissues. Cartilaginous tissues such as articular cartilage and the annulus fibrosus are collagen fiber-reinforced composites that exhibit orthotropic behavior and highly asymmetric tensile-compressive responses. They also experience finite deformations in vivo. Successful integration with surrounding tissue upon implantation likely will require cartilage constructs to have similar structural and functional properties as native tissue. Reliable stress constitutive equations that accurately characterize the tissue's mechanical properties must be developed to achieve this aim. Recent studies have successfully implemented bimodular theories for infinitesimal strains (Soltz et al., 2000; Wang et al., 2003); those models were based on the theory of Curnier et al. (1995). The objective of this work was to develop a more accurate cartilage stress constitutive equation for finite strains. Specifically, the first aim was to derive an orthotropic bimodular stress-strain equation with three surfaces of discontinuity. The second aim was to assess the ability of the equation to simultaneously describe the nonlinear tensile and compressive responses in three orthogonal directions for the superficial region of articular cartilage.