The goal of this proposal is to develop the osteochondral HyCart product to enable resurfacing of entire knee joint compartments and repair of defects up to 20cm2 in articular cartilage of the knee joint. The HyCart implant will be custom-shaped to the defect and consist of engineered cartilage functionally interdigitated to nano-hydroxyapatite (nHA). As articular cartilage lacks the ability to properly mount a healing response, injuries to this tissue, through trauma or wear-and-tear, persist and can lead to osteoarthritis. In an attempt to regain normal joint function and halt these delterious changes, over 400,000 surgeries are performed in the USA every year to treat injuries to articular cartilage. The current and prospective biologic treatment options suffer from a number of significant drawbacks including the inability to repair large defects, insufficient integration of repair cartilage, and fibrous repair tissue that degrades over time. HyCart will alleviate these problems by 1) enabling biologic repair of large, compartmental defects; 2) providing a biomechanically mature articular cartilage surface; 3) encouraging stable fixation into the joint through bone-nHA integration; and 4) promoting neocartilage-cartilage integration by high cellularity. The 1st Aim focuses on identifying an appropriate time to mate the cartilaginous and bony portions of HyCart that will maximize functional interdigitation. The 2nd Aim focuses on identifying the maturational level of HyCart that is most conducive to integration with adjacent native osteochondral tissue. The primary success criterion of both Aims will be the mechanical integrity of interdigitation or integration. Secondarily, the quality of the engineered osteochondrl tissue will be determined by a battery of biomechanical, biochemical, and histological assessments to ensure tissue functionality. This Phase I proposal will establish feasibility for th HyCart product Phase II studies, additional product development, and eventual clinical testing. Development of this innovative product will enable clinicians, for the first time, to biologically resurface entire joint compartments and effectively treat focal injuries to articular cartilage, ths lowering the incidence of osteoarthritis.