Biphasic xenograft pairs for in vivo autogenous bone formation

Monophasic anorganic bone grafts such as Bio-Oss^®, OsteoGen™ and OsteoGraft™ have achieved commercial success as xenografts in dentistry and maxillofacial surgery. Integration of these bone substitutes with host tissue is facilitated by the chemical and crystalline similarity of anorganic bone, which is carbonated hydroxyapatite (Hap). Biphasic hydroxyapatite containing 20 – 30% beta-tricalcium phosphate (β–TCP), on the other hand, is known to possess better in vivo resorption that leads to better adhesion of bone growing cells as well as better osseointegration and remodeling at the deployment site. In this work, we report successful preparation of a biphasic xenograft from anorganic bone and demonstrates its efficacy in stimulating bone repair in vivo. Bovine bone was first calcined to produce monophasic (Hap) and biphasic (Hap and β–TCP) precursors, which were then ground and sintered. Bone augmentation performance of these two sintered xenografts was then studied in vivo by placing them side by side in contact with the Volkmann canals of the periosteum on rabbit tibias without causing any perforation or fracture to the host bone. We also placed two to three sintered xenografts along the tibia to study host bone - graft and graft - graft interactions. Five weeks after the surgical deployment, a new bone mass in the form of a collar was observed at the interface between each of the grafts and the host bone. A small bridge was also created between each pair of grafts due to their own interactions. The biphasic graft allowed a relatively thick layer of new bone mass to grow when compared to the monophasic graft within the same time after deployment. Both grafts showed a formation of organic fibers but vascularization (appearance of pores) at the graft/host bone interface was better for the biphasic graft. X–ray Diffractometer (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, and Scanning Electron Microscopy (SEM) carried out on newly generated bone mass as well as the deployed grafts showed that the presence of better resorbing β–TCP in the biphasic graft accelerated bone regeneration in vivo compared to a monophasic graft.