Accelerated repair of a bone defect with a synthetic biodegradable bone-inducing implant

Abstract

BackgroundNothing has ever had osteoinductive capacity and degradability equivalent to that of autogenous bone, although many types of biomaterials have been developed. To address this issue, we constructed a new bone graft substitute with osteogenic potential and degradability by using porous beta-tricalcium phosphate (β-TCP) granules, bone morphogenetic protein (BMP), and a synthetic block copolymer composed of poly-d,l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG). In this experimental study, the bone-inducing capacity and degradation properties of the composite implant during the bone healing process were examined in vivo in a cortical and cancellous bone defect model in rabbits. MethodsThe advantages of this type of implant have been examined in a cortical bone defect model created in the distal femur of rabbits. The defects (6.5×5mm) were filled with 30 mg of various implants: BMP-H [rhBMP-2, 0.0025% (w/w)], BMP-L [rhBMP-2, 0.000625% (w/w)], control A (β-TCP alone), and control B (no implant). The distal femurs were harvested at scheduled intervals after surgery and examined for the evaluation of the bony repair of the defects by threedimensional computed tomography and histology. ResultsThe repair of both cortical and cancellous bone occurred predominantly in the BMP-H group, and only minor cortical bone repair and cancellous bone formation were noted in the BMP-L and control A groups. Most of the β-TCP was resorbed in the BMP-H group at 6 weeks after surgery, whereas a significant amount of β-TCP remained in the BMPL and control A groups. Conclusionsβ-TCP granules coated with a BMP-retaining synthetic polymer appear to be effective in enhancing the repair of both cancellous and cortical bone defects. The early disappearance of the implanted β-TCP and restoration of the normal anatomy of bone tissue are two notable features of this approach.