Preclinical evaluation of a xenogenic hydroxyapatite/ collagen-based bone substitute material

Objective: The aim of this study was to evaluate the physical, chemical and biological properties of a bovine xenograft for bone repair. Methods: Physicochemical analysis was performed using X-ray diffraction, Fourier transform infrared spectroscopy and scanning eletron microscopy. In vitro biocompatibility was evaluated through cytotoxicity and cell adhesion assays using a fibroblast cell line culture and murine pre-osteoblasts, respectively. Furthermore, an in vivo assay using a subcutaneous grafting on a rat model (5 and 10 weeks, synthetic hydroxyapatite as a control material) and yet a long term experiment in criticalsize calvarial defects (6 and 9 months, blood clot and autogenous bone as negative and positive controls, respectively). Results: The test material presented a three-dimensional architecture consisting of dense granules and micropores (various sizes), composed of crystalline hydroxyapatite/collagen fibers. The xenograft was cytocompatible and after 7 days pre-osteoblast spreading on material granules was observed. Histopathological analysis of the implanted material into rat subcutaneous showed the intact xenograft after 10 weeks surrounded by loose connective tissue with a mild inflammatory infiltrate and giant multinuclear cells around the particles (5 and 10 weeks) similar to the synthetic hydroxyapatite. Concerning the critical-size calvarial defects it was observed 1.7 times more new bone formation in the xenograft than the blood clot group (P<0.001), a similar result was verified on autograft. There was no significant variation in the volume density of the xenograft (37.9%±4.3). Conclusion: It was concluded that the xenogenic material is biomimetic, biocompatible, osteoconductive and non-resorbable, therefore being a promising material for bone repair.