Enhancing bioactivity of chitosan film for osteogenesis and wound healing by covalent immobilization of BMP-2 or FGF-2.

This study compares the efficacy of growth factors that are covalently immobilized to those that are adsorbed in improving the bioactivity of a biomaterial. Bone morphogenetic protein-2 (BMP-2) or fibroblast growth factor-2 (FGF-2) was covalently bonded to chitosan films using carbodiimide chemistry. For BMP-2, a growth factor loading efficiency of ∼64% was obtained with this method compared to ∼25% from adsorption. As for FGF-2, the growth factor loading efficiency of the two methods was similar at ∼50%. The covalently immobilized BMP-2 promoted attachment, proliferation, and differentiation of osteoblasts in a dose-dependent manner, whereas the covalently immobilized FGF-2 stimulated fibroblast attachment, proliferation, and collagen synthesis. After three weeks immersion in phosphate buffered saline, about 80% of the covalently immobilized growth factors were retained on the films, while only ∼16 and ∼21% of the adsorbed BMP-2 and FGF-2 remained on the corresponding films. The higher retention rate of the covalently immobilized growth factors enabled their stimulatory effects to persist for a longer period than when adsorbed growth factors were used.