Finite Element Analyses of Articular Cartilage Models Considering Depth-Dependent Elastic Modulus and Collagen Fiber Network

Articular cartilage has high water content and biphasic property. The structures of the tissue are inhomogeneous and anisotropic. Furthermore, the mechanical behavior of cartilage shows depth-dependence. Therefore it is necessary to consider not only the average tissue property but also the local one to explain mechanical and functional behavior. Previously, we created two-dimensional biphasic finite element (FE) cartilage tissue models considering the depth-dependence of elastic modulus distribution based on experimental results. As a result, this finding indicates that the depth-dependence of elastic modulus has a remarked influence on the deformed profile. In this study, the effectiveness of collagen fiber network in addition to the depth-dependent elastic modulus of cartilage tissue is evaluated. By creating of cartilage tissue models using axisymmetric biphasic elements and spring elements, we analyzed the unconfined compressive behaviors of articular cartilage specimens and compared the FE analyses to experimental results. Every FE model has depth-dependence of elastic modulus based on our previous formula, while the Poisson's ratio and permeability of solid phase were assumed as constant in literature data. To compare experimental result with finite element analysis (FEA), boundary conditions for FEA were given to correspond to the compression test. As a result, total load capacity and deformed profiles immediately after compression of FEA simulation on eventual model corresponded to experimental results by controlling spring constant. Furthermore, local strain of axial direction in FEA results for eventual model and experimental ones show the same tendency about time-dependent change. Then, we considered intrinsic fluid flow of eventual model.