An in vitro model of biomaterial-augmented microfracture including chondrocyte–progenitor cell interaction

Background Biomaterials, acting as scaffolds for cell migration and differentiation, may be used to improve outcomes after microfracture. Three mechanisms determine the success of such procedures and are tested herein: the general capacity of adult femoral mesenchymal progenitor cells (MPC) to differentiate into cartilage, their capacity to do so in a biomaterial, and finally potential interactions between MPC and autologous chondrocytes. Methods Human adult chondrocytes and MPC were obtained with informed consent and cultured individually or in co-culture on a collagenous biomaterial. Differentiation potential of MPC was assessed using PCR and proliferation and biosynthesis were compared to test for differences between individual cultures and co-cultures. Finally, potential interaction between chondrocytes and MPC was assessed by comparing the observed levels of proliferation and biosynthesis with those expected in independent growth. Results We found that adult femoral marrow-derived MPC have the potential to differentiate into multiple lineages, and, seeded in a biomaterial, show similar differentiation when compared with autologous chondrocytes. Finally, there was a strong indication for an interaction between MPC and chondrocytes in biosynthetic activity, which was twice as high as would be expected in independent cell activity. Proliferation rates were unaffected. Conclusion Our study showed that biomaterial-augmented microfracture is a viable option in cartilage repair from a biological perspective because adult femoral MPC have a strong capacity to differentiate into chondrocytes, which is further enhanced by the surrounding cartilage. Failure in in vivo studies must be explained by other factors of the intra-articular environment, such as cytokines or biomechanics.