| Articular cartilage lines the surfaces of synovial joints to protect underlying bone and provide a smooth surface for articulation. Damage to articular cartilage typically leads to long-term pain and disability, as current treatments are unable to fully restore the functional tissue. Thus, tissue engineers seek to develop technologies to enhance cartilage repair. This thesis investigated two strategies for cartilage engineering: flow perfusion bioreactor culture and co-cultures of chondrocytes with mesenchymal stem cells (MSCs). First, we designed a novel bioreactor and then investigated the effect of flow perfusion on chondrocytes when combined with chondrogenic stimuli, including hypoxia and transforming growth factor-beta3 (TGF-beta3). We demonstrated that the combination of flow perfusion and hypoxic conditions enhanced proliferation, cartilage-like extracellular matrix production, and chondrogenic gene expression compared to perfusion alone. However, these results also demonstrated the need for a more potent chondrogenic stimulus, and thus the effect of perfusion with TGF-beta3 was investigated on both chondrocytes and co-cultures of chondrocytes and MSCs. Here, we described the advantages of using exogenous growth factors in flow perfusion cultures, and the utility of flow perfusion for creating large tissue-engineered constructs. The second part of this thesis investigated co-cultures of chondrocytes and MSCs having the potential to reduce the demand for chondrocytes, which overcomes a significant challenge to current approaches toward cartilage repair. We first investigated the sensitivity of this cell population to TGF-beta3 and then investigated the stability of the cell phenotype resulting from growth factor supplementation. The results demonstrated that co-cultures of chondrocytes and MSCs enable a reduced concentration and duration of TGF-beta3 exposure to achieve an equivalent level of chondrogenesis compared to chondrocyte or MSC monocultures. Thus, the present work implicates that the promise of co-cultures for cartilage engineering is enhanced by their robust phenotype and heightened sensitivity to TGF-beta3. The final section of this thesis investigated the ability of such co-cultures to repair cartilage in a rat osteochondral defect model. Here, it was demonstrated that co-cultures achieved equivalent cartilage repair compared to the chondrocytes, thus demonstrating the potential use of co-cultures of articular chondrocytes and MSCs for the in vivo repair of cartilage defects. |
