Simulated intervertebral disc-like assembly using bone marrow-derived mesenchymal stem cell sheets and silk scaffolds for annulus fibrosus regeneration

Most studies on the intervertebral disc (IVD) focus on the regeneration of the nucleus pulposus (NP). However, without a proper strategy to regenerate the damaged annulus fibrosus (AF), the NP replacements are bound to fail. Therefore the objective of this study was to investigate whether the use of bone marrow-derived mesenchymal stem cells (BMSCs) to form cell sheets, and incorporating them onto silk scaffolds, has the potential to regenerate the annulus fibrosus. The BMSC cell sheets and silk scaffolds were wrapped around a silicone NP substitute to form a simulated IVD-like assembly. The simulated IVD-like assembly was cultured for 4 weeks in static conditions and it was shown that the BMSC cell sheets remained viable, with no significant change in cell numbers. Histological analysis showed that the BMSC cell sheets adhered well onto the silk scaffolds and glycosaminoglycans (GAGs) were detected within the extracellular matrix (ECM). The ratio of collagen type I to collagen type II within the ECM of the BMSC cell sheets also decreased significantly over the period of culture. The results suggested that extensive remodelling of the ECM occurred within the simulated IVD-like assembly, and it is suitable for the regeneration of the inner AF.