Implantation study of a novel hydroxyapatite/collagen (HAp/col) composite into weight‐bearing sites of dogs

Abstract

A hydroxyapatite/type I collagen (HAp/Col) composite, aligning hydroxyapatite nanocrystals along collagen molecules, has been prepared. The biocompatibility, osteoconductive activity, and efficacy as a carrier of rhBMP‐2 of this novel biomaterial implanted in the weight‐bearing site have been examined. The HAp/Col implants (15 mm in diameter and 20 mm in length) with a surface cross‐linked layer containing rhBMP‐2 (0 or 400 μg/ml) were implanted into bone defects of tibiae in three beagle dogs and fixed according to the Ilizarov method. As a control, bone defects of 20 mm in two beagle dogs did not receive implants, and the dogs were allowed to walk using an Ilizarov extraskeletal fixator. The specimens were removed from one dog in each group after 12 weeks. Also, the Ilizarov fixators in the rhBMP‐treated dogs were removed after 12 weeks, after which full weight bearing started. The specimens were further taken out after 18 and 24 weeks in the rhBMP‐treated and non‐rhBMP‐treated dogs, and after 24 weeks in the control group. The change of bone mineral density, as well as radiological and histological findings, suggest that the implants are able to induce bone remodeling units and are a superior carrier of rhBMP‐2 due to the stimulation of early callus and new bone formation. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 507–515, 2002