Repair of segmental defects in rabbit humeri with titanium fiber mesh cylinders containing recombinant human bone morphogenetic protein-2 (rhBMP-2) and a synthetic polymer

To develop a new technology that enhances the regeneration potential of bone and the repair of large intercalated defects in long bone, recombinant human bone morphogenetic protein-2 (BMP-2; 20 microg or 40 microg) was mixed in a polymer gel (poly-lactic acid-polyethyleneglycol block copolymer; PLA-PEG; 200 mg) and incorporated into titanium fiber-mesh cylinders. Three 5-mm cylinders were placed end-to-end to fill a 15-mm defect created in the humeri of adult rabbits and were stabilized by an intramedullary rod. In controls, the titanium fiber-mesh cylinders were combined with PLA-PEG in the absence of BMP. Six weeks after implantation, new bone had formed on the surface of the implant and had bridged the defect. All of the defects (5/5) treated by cylinders containing 120 microg (40 microg x 3) of BMP were repaired completely. New bone formation was also found inside the pores of the cylinders. The defect was not repaired in the control animals. These results demonstrate that these new composite implants fabricated by combining rhBMP, synthetic degradable polymers and compatible biomaterials enhance the regeneration potential of bone. Thus, it is possible that large skeletal defects can be repaired using this prosthesis in lieu of autogenous bone graft.