Microencapsulation and chondrogenic differentiation of human mesenchymal progenitor cells from subchondral bone marrow in Ca-alginate for cell injection

The application of stem cells is a promising therapeutic approach for cartilage regeneration. For cell therapies, a biocompatible injectable carrier, which improves retention and cell distribution and enables cell differentiation, is a prerequisite. In this study, Ca-alginate microcapsules containing human subchondral cortico-spongious progenitor cells were prepared and the chondrogenic differentiation potential was verified by real-time reverse transcription-polymerase chain reaction analysis of typical chondrogenic marker genes. The results confirmed that these cells were able to differentiate along the chondrogenic lineage when encapsulated in Ca-alginate microcapsules with a mean diameter of 600–700 μm and stimulated with TGF-beta3. Chondrogenic marker genes type II collagen, aggrecan and cartilage oligomeric matrix protein were induced together with type I collagen, whereas adipogenic and osteogenic marker genes showed no induction over 14 days. After 28 days, proteoglycans and type II collagen were evident histochemically and immunohistochemically. Mechanical stability as well as permeability of Ca-alginate capsules were analysed over the course of cultivation and found to be qualified for stable cell immobilization and sufficient exchange of solutes. Therefore, from the cell biology point of view, Ca-alginate, an established hydrogel scaffold material is suited for regenerative therapies of cartilage defects based on the injection of progenitor cells.