Preparation and characterization of chitosan microspheres for controlled release of synthetic oligopeptide derived from BMP-2.

The localized and temporally controlled release of growth factors is key to achieving optimal clinical efficacy. To achieve sustained delivery of a novel bone-induced growth factor, chitosan microspheres loaded with synthetic oligopeptide (S([PO4])KIPKASSVPTELSAISTLYLDDD, P24) were prepared by an emulsion-ionic cross-linking method in the presence of tripolyphosphate, with bovine serum albumin (BSA) as a control. Both microspheres containing oligopeptide or BSA were of spherical shape with size ranging from 10-60 µm. The encapsulation efficiency was usually higher than 80% and the loading capacity was affected by initial protein dosage. From the release experiments, it was found that both proteins were slowly released from the microspheres over 7 days in a PBS solution (pH 7.4), in which the release rate of oligopeptide was much lower than that of BSA. Released oligopeptide was demonstrated to possess biological activity as evidenced by stimulation of rabbit marrow mesenchymal stem cells (MSCs) alkaline phosphatase (ALP) activity in vitro. These results indicate that the TPP-chitosan microspheres loaded with synthetic oligopeptide may possess potential application in bone tissue engineering.