Accelerated repair of a bone defect with a synthetic biodegradable bone-inducing implant.
BACKGROUND
Nothing 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 (beta-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.


METHODS
The 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 x 5 mm) 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 (beta-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 three-dimensional computed tomography and histology.


RESULTS
The 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 beta-TCP was resorbed in the BMP-H group at 6 weeks after surgery, whereas a significant amount of beta-TCP remained in the BMP-L and control A groups.


CONCLUSIONS
beta-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 beta-TCP and restoration of the normal anatomy of bone tissue are two notable features of this approach.
Matsushita
Naofumi
N
Department of Orthopaedic Surgery, Osaka City University School of Medicine, 1-4-3 Asahi-machi, Abeno-ku, Osaka, 545-8585, Japan.
Terai
Hidetomi
H
Okada
Takao
T
Nozaki
Kazutoshi
K
Inoue
Hikaru
H
Miyamoto
Shimpei
S
Takaoka
Kunio
K
D020341:Absorbable Implants; D000818:Animals; D001672:Biocompatible Materials; D001847:Bone Diseases / Q000000981:diagnostic imaging / Q000601:surgery*; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002130:Calcium Phosphates / Q000494:pharmacology*; D004195:Disease Models, Animal; D008297:Male; D019919:Prosthesis Implantation / Q000295:instrumentation*; D011817:Rabbits; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
D001672:Biocompatible Materials; D019485:Bone Morphogenetic Proteins; D002130:Calcium Phosphates; C485817:beta-tricalcium phosphate