Initiation of mesenchymal condensation in alginate hollow spheres--a useful model for understanding cartilage repair?

A promising strategy for the regeneration of degenerated cartilage tissue structure in osteoarthritic joints is the use of mesenchymal precursor cells. These cells can be triggered to undergo differentiation into functional active chondrocytes resulting in newly synthesized cartilage. Because chondrogenic differentiation is initiated by the step of mesenchymal condensation in vitro, it is of great interest to fully characterize the first lineage specific step in vitro. Therefore, a modified culture system was developed which mimics the process in vitro and may finally help to identify the key factors that are essential for the induction of chondrogenic differentiation in vivo. Compared to other established 3D culture systems like alginate beads and micromass cultures, the use of alginate hollow spheres bears the advantage to analyze different phases of cell aggregation starting from a single cell suspension of previously isolated and expanded human primary cells of mesenchymal origin.