Gelatin microspheres releasing transforming growth factor drive in vitro chondrogenesis of human periosteum derived cells in micromass culture

For cartilage tissue engineering, several in vitro culture methodologies have displayed potential for the chondrogenic differentiation of mesenchymal stem cells (MSCs). Micromasses, cell aggregates or pellets, and cell sheets are all structures with high cell density that provides for abundant cell-cell interactions, which have been demonstrated to be important for chondrogenesis. Recently, these culture systems have been improved via the incorporation of growth factor releasing components such as degradable microspheres within the structures, further enhancing chondrogenesis. Herein, we incorporated different amounts of gelatin microspheres releasing transforming growth factor β1 (TGF-β1) into micromasses composed of human periosteum derived cells (hPDCs), an MSC-like cell population. The aim of this research was to investigate chondrogenic stimulation by TGF-β1 delivery from these degradable microspheres in comparison to exogenous supplementation with TGF-β1 in the culture medium. Microscopy showed that the gelatin microspheres could be successfully incorporated within hPDC micromasses without interfering with the formation of the structure, while biochemical analysis and histology demonstrated increasing DNA content at week 2 and accumulation of glycosaminoglycan and collagen at weeks 2 and 4. Importantly, similar chondrogenesis was achieved when TGF-β1 was delivered from the microspheres compared to controls with TGF-β1 in the medium. Increasing the amount of growth factor within the micromasses by increasing the amount of microspheres added did not further improve chondrogenesis of the hPDCs. These findings demonstrate the potential of using cytokine releasing, gelatin microspheres to enhance the chondrogenic capabilities of hPDC micromasses as an alternative to supplementation of the culture medium with growth factors.