Assessment of cartilage graft maturation in vitro

Osteoarthritis (OA) represents a considerable societal and economic burden in today’s society. Despite the tremendous developments in the field of articular cartilage tissue engineering (AC TE) in the recent decade, none of the TE-based approaches has been able to regenerate the cartilage to levels of native tissue. The established paradigm of AC TE involves employment of undifferentiated MSCs in combination with 3D scaffolds/hydrogels and appropriate growth factors to induce chondrogenic differentiation of cells and deposition of ECM components like collagen and glycosaminoglycans. Once successful tissue has been formed in vitro, engineered cartilage grafts can be studied in vivo in large animal models to assess safety and efficacy of such grafts. Unfortunately, a considerable amount of grafts fails in vivo, which indicates the overall unsuitability and immaturity of the engineered tissues to function in the mechanically demanding environment of the joint in vivo. More importantly, there is no incentive to publish or submit for publication unsuccessful studies, which indicates that the number of failed studies employing large animal models could be considerably higher. Therefore, there is a need for novel strategies to screen and identify in vitro engineered cartilage grafts that have higher chances of success in vivo. In addition to increasing the success rate of such studies, this approach would have a great potential to reduce the number of animals utilized in such studies. In this context, there is evidence suggesting that chondrogenically differentiating MSCs respond anabolically to mechanical stress at later stages of differentiation by producing ECM components like glycosaminoglycans. Interestingly, the differentiation of MSCs is also associated with metabolic changes, where glycolysis is reduced and oxidative phosphorylation is enhanced as maturation progresses. The goal of this project is to develop a platform that could be used to assess such metabolic changes by sampling metabolites in- and outside the developing cartilage grafts to make statements concerning the maturity. By establishing such platform an additional readout would be available, in addition to commonly used biochemical and histological techniques within AC TE, that would facilitate a more informed decision making prior to an in vivo transition of a potential cartilage graft.