Biomechanical properties and mechanobiology of the articular chondrocyte.

To withstand physiological loading over a lifetime, human synovial joints are covered and protected by articular cartilage, a layer of low-friction, load-bearing tissue. The unique mechanical function of articular cartilage largely depends on the composition and structural integrity of the cartilage matrix. The matrix is produced by highly specialized resident cells called chondrocytes. Under physiological loading, chondrocytes maintain the balance between degradation and synthesis of matrix macromolecules. Under excessive loading or injury, however, degradation exceeds synthesis, causing joint degeneration and, eventually, osteoarthritis (OA). Hence, the mechanoresponses of chondrocytes play an important role in the development of OA. Despite its clear importance, the mechanobiology of articular chondrocytes is not well understood. To summarize our current understanding, here we review studies of the effect of mechanical forces on mechanical and biological properties of articular chondrocytes. First, we present the viscoelastic properties of the cell nucleus, chondrocyte, pericellular matrix, and chondron. Then we discuss how these properties change in OA. Finally, we discuss the responses of normal and osteoarthritic chondrocytes to a variety of mechanical stimuli. Studies reviewed here may provide novel insights into the pathogenesis of OA and may help in development of effective biophysical treatment.