Chondrogenesis and integration of mesenchymal stem cells within an in vitro cartilage defect repair model

Abstract

Integration of repair tissue is a key indicator of the long-term success of cell-based therapies for cartilage repair. The objective of this study was to compare the in vitro chondrogenic differentiation and integration of agarose hydrogels seeded with either chondrocytes or bone marrow derived mesenchymal stem cells (MSCs) in defects created in cartilage explants. Chondrocytes and MSCs were isolated from porcine donors, suspended in 2% agarose and then injected into cylindrical defects within the explants. These constructs were maintained in a chemically defined medium supplemented with 10 ng/ml of TGF-β3. Cartilage integration was assessed by histology and mechanical push-out tests. After 6 weeks in culture, chondrocyte seeded constructs demonstrated a higher integration strength (64.4 ± 8.3 kPa) compared to MSC seeded constructs (22.7 ± 5.9 kPa). GAG (1.27 ± 0.3 kPa vs 0.19 ± 0.03 kPa) and collagen (0.31 ± 0.08 kPa vs 0.09 ± 0.01 kPa) accumulation in chondrocyte seeded constructs was greater than that measured in the MSC seeded group. The GAG, collagen and DNA content of both chondrocyte and MSC-seeded hydrogels cultured in cartilage explants was significantly lower than control constructs cultured in free swelling conditions. The results of this study suggest that the explant model may constitute a more rigorous in vitro test to assess MSC therapies for cartilage defect repair.