Generation of an osteochondral interface using rabbit mesenchymal stem cells and collagen gel

Abstract

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. In a separate rabbit cartilage repair model, preliminary data showed excitingly promising results. At 1 month post-operation, the natural healing side was filled with massive reparative tissue, which was covered by a thick fibrous tissue negative for chondrogenic markers. On the microsphere repaired side, a pale yellow with shiny white gross appearance, characteristic to hyaline cartilage, was observed. In only 1 month’ time, the repaired osteochondral tissue showed excellent zonal organization with a tidemark denoting the beginning of the calcified interface, which separates the upper non-calcified chondrogenic microsphere layer and the underlying osteogenic microsphere layer. This encouraging outcome demonstrates the importance of appropriate zonal organization in cartilage repair. A full scale animal study is underway.