A parametric study on the mechanical role of fibrillar rotations in an articular cartilage finite element model

Collagen network is one of the articular cartilage (AC) vital components, which contributes to the depth-dependent and anisotropic response of the tissue. As it is computationally expensive to simulate all the structural details of the AC network, they were typically simplified in numerical analysis. In particular, the so-called arcade-like structure, which has been widely used in the previous complex simulations, does not capture the rotations of the fibrillar bundles. In this study, we investigate the role of such possible rotations in the AC mechanical response by a set of advanced, biphasic, and parametric finite element (FE) simulations of indentation tests. Our results unveil the influence of fibrillar rotation (FR) on the mechanical response by increasing the fibrillar stress while regionally affecting the stress in the upper layers of the AC tissue. On the contrary, the FR did not significantly alter the tissue elasticity, and consequently might be ignored safely in pure contact mechanical problems. It is concluded that the excessive FR might regionally increase the stress, which can have a degenerative effect on the collagen constituent, and therefore, should not be neglected in the corresponding future studies, in which the upper AC layers resist high permanent shear strains.