Synthesis and characterization of photocrosslinked gelatin-silk fibroin composite microspheres for mesenchymal stem cell expansion and osteogenic differentiation

Microspheres have shown great potential as biomaterial substrates for culturing and expanding stem cells to meet the requirements of cell therapy. Gelatin microspheres have been widely researched in cell culture; however, the size, pore structure, and stability of these microspheres still need to be further optimized. In this study, gelatin methacrylamide (GelMA) and glycidyl-methacrylate-modified silk fibroin (SFMA) composite microspheres (denoted as GSM microspheres) were synthesized using a simple water-oil (W/O) emulsion method followed by photo-crosslinking. The swelling ratio (34 % (w/v) GelMA = 799.8 ± 67.7 %; 34 % (w/v) GSM = 643.1 ± 66.3 %) and degradation ratio (relative weights at 15 d: 34 % (w/v); GelMA = 13.3 ± 3.9 %; 34 % (w/v) GSM = 38.6 ± 6.2 %) of GSM microspheres decreased with the incorporation of SFMA. Moreover, the constructed microspheres demonstrated adjustable size distribution (from 75 to 775 µm for GM0 to 25–275 µm for GSM3), pore structure, and surface curvature. Thus, the initial cell adhesion efficiency of microspheres increased with the content of GelMA (GSM1, GSM2, and GSM3 was 39.5 %, 23.3 %, and 7.7 %, respectively), and the cell amplification achieved by microsphere-microsphere transfer demonstrates the potential for cell expansion in vitro . In addition, On the higher curvature surface of GSM3, the cells were overspread and the shape factor of the nucleus was high (0.88 ± 0.05). Alkaline phosphatase (ALP) activity, osteogenesis-related gene expression, and Alizarin Red S staining showed that the addition of SFMA could promote osteogenic differentiation of BMSCs. Thus, the composite microspheres can serve as an adjustable three-dimensional (3D) culture platform for the amplification and osteogenic differentiation of BMSCs.