Biomimetic coatings vs. collagen sponges as a carrier for BMP-2:: A comparison of the osteogenic responses triggered in vivo using an ectopic rat model

We have developed a new carrier system for bone morphogenetic protein 2 (BMP-2). This agent has been successfully incorporated into biomimetic calcium phosphate implant coatings without losing its osteoinductive potency. Numerous materials have been tested for their efficiency in carrying BMP-2 and in promoting its osteoinductive effects at both ectopic and orthotopic sites. In the present study, we compare the osteoinductive effects of BMP-2 delivered by biomimetic coatings and by classical collagen sponges in vivo using an ectopic rat model. Titanium-alloy discs, either bearing a co-precipitated layer of calcium phosphate and BMP-2 (1.7 mug/disc) or inserted into collagen sponges impregnated with the same drug (10 mug/sponge), were implanted subcutaneously in the dorsal region of rats and the bone-formation process monitored after 2 and 5 weeks. After 2 weeks, the net volume of bone formed in the biomimetic coating group (5.8 mm(3)/disc) was greater (p < 0.01) than in the collagen sponge one (2.3 mm(3)/sponge). By the end of the fifth week, the net volume of bone deposited had increased significantly (p < 0.001) in the biomimetic coating group (11.6 mm(3)/disc), whereas in the collagen sponge one it remained unchanged (3.0 mm(3)/sponge; p = 0.82). As a carrier for BMP-2 and in facilitating its osteogenic effects, biomimetic calcium phosphate coatings offer a distinct advantage over the classical collagen sponge.