Modelling the triphasic mechanics of porous material in articular cartilage

The unique mechanical properties of porous media in the articular cartilage have been attributed to the complex structure and the composition of the extracellular matrix, which consists of water and an air phase and a solid matrix that is composed of a fibrous network of collagen and aggregating cells. This paper employs a recent constitutive model to summarise the important characteristics of the mechanics of porous media in the articular cartilage. The constitutive functions are described as follows: the evolution of the constitutive effective stress with imposed solid matrix deformation; the intrinsic mass densities with intrinsic pressure on all three phase; and the relative flow vector with intrinsic pressure for the water and air phase. The progression of the deformation in large-scale boundary value problems under monotonic loading conditions has been mapped based on the summarised mechanical characteristics. Simulations are presented to demonstrate how the proposed criterion can be applied to real-world situations. The methodology proposed herein provides a powerful means of assessing articular cartilage mechanics based on a solid mechanical theory rather than empiricism.