Effect of the structure of bone morphogenetic protein carriers on ectopic bone regeneration

To study the effect of the shape of carriers on bone regeneration, two biodegradable polymeric materials, a polyglycolide (PGA) nonwoven fabric and a gelatin hydrogel, were used as carriers of recombinant human bone morphogenetic protein-2 (rhBMP-2). The PGA nonwoven fabric was made from PGA fibers of 20 microm diameter without using any binders while the gelatin hydrogel was prepared by cross-linking of gelatin in aqueous solution with glutaraldehyde to a water content of 95% when swollen with water. Following impregnation of rhBMP-2, the carriers of disk type were implanted into the Wistar rat thigh muscle. The induction of ectopic bone formation from the rhBMP-2-impregnated carriers was evaluated by Softex and histologic observation after staining the explanted tissue with alizarin red S stain to identify calcium deposition. Both of the biodegradable polymeric carriers containing 10 microg of rhBMP-2 induced ectopic bone formation after 2 weeks of implantation but not at the first week after implantation. A remarkable finding was a difference in the macroscopic morphology between the ectopic bones induced by the PGA nonwoven fabric and the gelatin hydrogel. The PGA nonwoven fabric containing rhBMP-2 induced ectopic bone formation inside of the carrier, whereas the gelatin hydrogel formed bone at the periphery of the carrier.