Development of a novel hydroxyapatite/collagen composite biomaterial

A hydroxyapatite/type I collagen (HAp/Col) composite, in which the hydroxyapatite nanocrystals align along the collagen molecules, was prepared. The biocompatibility, osteoconductive activity and efficacy as a carrier of recombinant human bone morphogenetic protein (rhBMP)-2 of this novel biomaterial were examined. The composite materials (4 x 4 x 1 mm(3)) were implanted in the back of Wistar rats, and specimens were collected for histological observations until week 24. The composite materials (5 x 5 x 10 mm(3)) containing rhBMP-2 (0, 200, 400 mug/ml) were grafted in radii and ulnae in beagle dogs. X-ray images were prepared, and specimens collected for histo logical observation at week 8 and 12. The implants (15 mm in diameter and 20 mm in length) containing rhBMP-2 (0, 400 mug/ml) were implanted in tibiae in beagle dogs and fixed with Ilizarov method. Soft X-ray images were prepared each week. The bone mineral density (BMD) was measured and the implants were harvested at 12, 18 and 24 weeks after surgery. X-ray images and histological findings for the composites support the idea that HAp/Col has a high osteoconductive activity and is able to induce bone-remodeling units. In cases where the implants are grafted at weightbearing sites, treatment with rhBMP (400 mug/ml) may be useful to shorten the time until bone union.