Articular cartilage lines the surfaces of joints and transmits the forces arising from locomotion. The poor ability of cartilage to self-repair has motivated efforts to engineer replacements that recapitulate this load-bearing function. While chondrocyte-laden constructs have been generated with near-native mechanical properties, limitations in chondrocyte availability may preclude their clinical use. Therefore, mesenchymal stem cells (MSCs), which can undergo chondrogenesis in 3D culture, have emerged as a promising alternative [1]. However, although MSCs deposit a cartilaginous matrix, mechanical and biochemical properties are lower than those achieved with chondrocytes [1, 2]. Using microarray analysis, we recently showed that limitations in functional MSC chondrogenesis may stem from incomplete or incorrect molecular induction; molecular differences were observed between donor-matched differentiated chondrocytes and newly differentiated MSCs over 8 weeks of culture [2]. While some genes remained consistently low in MSCs compared to chondrocytes, others gradually increased with time, approaching chondrocyte levels by 8 weeks. As these molecules may underlie the functional disparity between chondrocytes and MSCs, we hypothesized that longer culture durations may improve MSC-seeded construct properties and chondrogenesis. To test this hypothesis, we characterized the evolution of functional properties of MSC- and chondrocyte-seeded constructs over 4 months of in vitro culture in pro-chondrogenic medium.

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