sequential delivery of bmp-2 and igf-1 using a chitosan gel with gelatin microspheres enhances early osteoblastic differentiation

the purpose of this study was to develop and characterize a chitosan gel/gelatin microsphere (mss) dual delivery system for sequential release of bone morphogenetic protein-2 (bmp-2) and insulin-like growth factor-1 (igf-1) to enhance osteoblast differentiation in vitro. we made and characterized the delivery system based on its degree of cross-linking, degradation, and release kinetics. we also evaluated the cytotoxicity of the delivery system and the effect of growth factors on cell response using pre-osteoblast w-20-17 mouse bone marrow stromal cells. igf-1 was first loaded into mss, and then the igf-1-containing mss were encapsulated into the chitosan gel which contained bmp-2. cross-linking of gelatin with glyoxal via schiff bases significantly increased thermal stability and decreased the solubility of the mss, leading to a significant decrease in the initial release of igf-1. encapsulation of the mss into the chitosan gel generated polyelectrolyte complexes by intermolecular interactions, which further affected the release kinetics of igf-1. this combinational delivery system provided an initial release of bmp-2 followed by a slow and sustained release of igf-1. significantly greater alkaline phosphatase activity was found in w-20-17 cells treated with the sequential delivery system compared with other treatments (p < 0.05) after a week of culture.