Influence of Degrading Calcium Phosphate on the Remodelling and Mineralisation of Avascular Osseous Tissue in a Rat Calvaria Model

Artificial bone graftingis the subject of intensive investigation for craniofacial reconstruction. Among the syntheticcandi date materials, those incorporating Calcium Phosphates (CaP) have gained popularity, due to their osteoinductive properties. Despite many quantitative studies on the degradation rates of CaP biomaterials in vitro, there is lack of quantitative studies in relation to bone remodelling kinetics in vivo. In this investigation, we tested implants of degradable CaP/chitosan-based biomaterial in a rat calvaria model of critical-sized defects. We observed remarkable acceleration of bone growth in the initial stages (~0.8 g/day), which was markedly higher than normal bone growth rates (~0.1 g/day) in implant-free controls. The implanted CaP-based biomaterial significantly enhanced bone formation, with woven bone seen as early as 20 days and lamellar bone at 40 and 60 days post-implantation. However the mineralisation of cortical bone was delayed, due to the overly rapid degradation of the biomaterial: This therapeutically important issue has never been identified before to our best knowledge. A theoretical analysis revealed that during degradation CaP can be rapidly released from the new bone matrix. Hence, while the degradable CaP biomaterial was found to be highly osteoconductive in vivo, future modifications would seek to optimize degradation efficiency for more sustained release of mineral ions, to enhance bone mineralisation at later stages of the healing process after implantation.