A fully coupled poroelastic reactive-transport model of cartilage

Cartilage maintains its integrity in a hostile mechanical environment. This task is made more difficult because cartilage has no blood supply, and so nutrients and growth factors need to be transported greater distances than normal to reach cells several millimetres from the cartilage surface. The chondrocytes embedded within the extracellular matrix (ECM) are essential for maintaining the mechanical integrity of the ECM, through a balance of degradation and synthesis of collagen and proteoglycans. A chondrocyte senses various chemical and mechanical signals in its local microenvironment, responding by appropriate adaption of the local ECM. Clearly a 'systems understanding' of cartilage behaviour is of critical importance in developing an integrated understanding of both normal and abnormal physiology of cartilage. In a series of papers, we have developed a reactive-transport porous-media model to investigate the coupled processes of growth factor transport, mechanical deformation and fluid flow, and in this paper, we extend the model to include biosynthesis and degradation of matrix molecules. The model is validated using three independent experimental data sets, it being found that a single set of parameters described the experimental results remarkably well. The model is then employed to make predictions about changes in proteoglycan content under a variety of conditions. This model may prove useful in predicting the behaviour of tissue engineering constructs, or predicting the outcome of repair processes in cartilage.