Bone morphogenetic protein-2 coating of titanium implants increases biomechanical strength and accelerates bone remodeling in fracture treatment: a biomechanical and histological study in rats.

Bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor (TGF)-beta superfamily, is known to be a very potent osteoinductive growth factor. The purpose of this study was to investigate the effect of BMP-2 (5% [w/w], 50 microg on each nail), locally released from poly(D,L-lactide) (PDLLA)-coated intramedullary implants, on fracture healing. A closed fracture of the right tibia of 5-month-old Sprague-Dawley rats (n = 64) was intramedullary stabilized with uncoated vs. BMP-2-coated titanium Kirschner wires. X-ray examinations (posteroanterior and lateral) were performed throughout the experiment. At 28 and 42 days after fracture, the animals were killed and both tibiae were dissected for biomechanical torsional testing. For histological and histomorphometric evaluation, 5 microm sections were obtained, stained with Safranin-O/light green and von Kossa, and examined using an image analysis system. The radiological results demonstrated progressed callus consolidation in the BMP-2-treated groups compared with the uncoated groups at both timepoints. Histomorphometric evaluation showed progressed callus remodeling with significantly increased mineralization and less cartilage of the periosteal callus. Due to the BMP-2 treatment, increased mineralization of the cortices was detected at 28 and 42 days after fracture. Biomechanical testing revealed significantly elevated maximum load and torsional stiffness in the BMP-2-treated groups compared with controls at both timepoints. The results clearly demonstrate that local application of BMP-2 from PDLLA-coated implants is feasible and significantly accelerates fracture healing. Local administration of growth factors from coated implants could reduce clinical problems in fracture treatment without opening of the fracture, implantation of further devices, or injection with the risk of infection or side effects caused by other carriers.