Articular cartilage bioreactors and bioprocesses.

This review summarizes the major approaches for developing articular cartilage, using bioreactors and mechanical stimuli. Cartilage cells live in an environment heavily influenced by mechanical forces. The development of cartilaginous tissue is dependent on the environment that surrounds it, both in vivo and in vitro. Chondrocytes must be cultured in a way that gives them the proper concentration of nutrients and oxygen while removing wastes. A mechanical force must also be applied during the culturing process to produce a phenotypically correct tissue. Four main types of forces are currently used in cartilage-culturing processes: hydrostatic pressure, direct compression, "high"-shear fluid environments, and "low"-shear fluid environments. All these forces have been integrated into culturing devices that serve as bioreactors for articular cartilage. The strengths and weaknesses of each device and stimulus are explored, as is the future of cartilage bioreactors.