Dynamic behavior of a biphasic cartilage model under cyclic compressive loading.

It is well known that dynamic mechanical loads can stimulate the biosynthetic activity of articular cartilage. Studying the mechanical environment of chondrocytes under dynamic loading conditions can help to explain this mechano-biological phenomenon in articular cartilage. In this study, the linear biphasic theory was used to examine the dynamic mechanical behavior of articular cartilage under a cyclic compressive force. We first studied the dynamic confined compression of a cartilage disk as a simplified one-dimensional model and then investigated the role of the relatively impermeable subchondral bone structure on the dynamic behavior of the cartilage extracellular matrix (ECM). Under an assumption of articular cartilage as a biphasic composite structure of a porous elastic solid matrix and interstitial fluid, the porous ECM of the articular cartilage was repeatedly compressed and expanded during the loading-unloading phases of the cyclic compressive force. One interesting finding of this study was the oscillating positive (supra-ambient)-negative (sub-ambient) hydrostatic pressure within the cartilage ECM under cyclic compressive loading. The pattern of the dynamic behavior of the cartilage ECM strongly depended on the loading frequency and the primary diffusion characteristic time, tau d. This finding is consistent with those of previous studies (Guilak et al., 1990 Adv Biomech. ASME, 225-228; Mow et al., 1990, Biomechanics of Diarthrodial Joints, pp. 215-260.