Approximately 95,000 total knee replacements and 41,000 other surgical procedures to repair cartilaginous defects of the knee are performed annually in the United States (1). The response of normal articular cartilage to injury or arthritic degeneration is often a sub-optimal repair; the biochemical and mechanical properties of the new tissue differ from the native cartilage, resulting in inadequate or altered function. It is believed that the chondrocytes from the surrounding areas, although perhaps capable of some limited migration at the damaged site, are not able to proliferate and produce the macromolecules necessary to create an organized matrix characteristic of normal articular cartilage (2,3). Current therapeutic options for articular cartilage injuries and degeneration have resulted in repair tissue which may be hyaline-like, but does not approximate the durability and function of the normal articular surface. Numerous studies have been performed to increase our understanding of the normal repair process of articular cartilage and its limitations, and to devise methods and materials to regenerate the joint surface.