Escherichia coli -derived BMP-2-absorbed β-TCP granules induce bone regeneration in rabbit critical-sized femoral segmental defects

Purpose This study investigated whether Escherichia coli -derived bone morphogenetic protein (BMP)-2 (E-BMP-2) adsorbed onto β-tricalcium phosphate (β-TCP) granules can induce bone regeneration in critical-size femoral segmental defects in rabbits. Methods Bone defects 20 mm in size and stabilized with an external fixator were created in the femur of New Zealand white rabbits, which were divided into BMP-2 and control groups. E-BMP-2-loaded β-TCP granules were implanted into defects of the BMP-2 group, whereas defects in the controls were implanted with β-TCP granules alone. At 12 and 24 weeks after surgery, radiographs were obtained of the femurs and histological and biomechanical assessments of the defect area were performed. Bone regeneration was quantified using micro-computed tomography at 24 weeks. Results Radiographic and histologic analyses revealed bone regeneration in the BMP-2 group but not the control group; no fracturing of newly formed bone occurred when the external fixator was removed at 12 weeks. At 24 weeks, tissue mineral density, the ratio of bone volume to total volume, and volumetric bone mineral density of the callus were higher in the BMP-2 group than in control animals. In the former, ultimate stress, extrinsic stiffness, and failure energy measurements for the femurs were higher at 24 weeks than at 12 weeks. Conclusion E-BMP-2-loaded β-TCP granules can effectively promote bone regeneration in long bone defects.