In vitro generation of an osteochondral interface from mesenchymal stem cell–collagen microspheres

Creating biological interfaces between mechanically dissimilar tissues is a key challenge in complex tissue engineering. An osteochondral interface is essential in preventing mechanical failure and maintaining normal function of cartilage. Despite tremendous efforts in developing osteochondral plugs, formation of the osteochondral interface with proper zonal organization has not yet been reported. Here, we present a mesenchymal stem cell–collagen microsphere-based approach for complex tissue engineering and demonstrate in vitro formation of a stem cell-derived osteochondral interface with calcified cartilage interface separating a non-calcified cartilage layer and an underlying bone layer. Cells at the interface region are hypertrophic chondrocytes while the extracellular matrix in this region contains collagen type II and X, calcium deposits and vertically running fibers. The simultaneous presence of appropriate medium and configuration during co-culture is necessary for the interface formation.