Integration of a collagen-hydroxyapatite scaffold into osteochondral cylinders from bovine knee joints : an in vitro study

Numerous techniques and treatments have been developed to prevent joint cartilage from degenerating or to restore its properties. One of these is MaioRegen® (MR) -a cell-free hybrid scaffold consisting of 3 collagen 1 layers with increasing hydroxyapatite content from the top cartilage to the bottom bone layer-, which demonstrated very promising results in clinical studies. A novel model was developed for the investigation of MR’s behavior in an in vitro setting. Ring-shaped osteochondral cylinders (outer diameter 8 mm; inner diameter 6 mm) were prepared from fresh bovine knee joints using standardized punches. Osteochondral autologous transplants or MR scaffolds with a diameter of 6 mm were then inserted into the osteochondral rings and cultured for periods of up to 10 weeks. Histological (HE, Safranin-O, and aggrecan immunohistology), transcriptional (collagen 1, 2, aggrecan, and COMP), biochemical (DMB assay, ELISA for collagen 1, 2 and aggrecan), and biomechanical analyses were performed at the start, as well as after 4, 8 and 10 weeks of in vitro culture. The culture system remained stable without signs of cell death or necrosis for any tissue component throughout 10 weeks of cell culture. In the OAT group, fibrocartilaginous tissue formation in the osseous part and a complete bridging of the gap between the osseous and transplant was observed after 8 weeks. Despite substantial cell migration into the scaffold, local proteoglycan deposition and increases in aggrecan gene expression, the MR scaffold progressively dissolved and thus showed decreased biomechanical resistances over time. The novel model appears suitable for high-throughput investigation of osteochondral regeneration in vitro. Due to its rapid degradation in vitro and in vivo, the MR scaffold may show limitations in the present in vitro model and in the clinical context of osteochondral regeneration.