Effect of P2O5 on mechanical properties of porous natural hydroxyapatite derived from cortical bovine bones sintered at 1,050 °C

In the current study, the effect of P2O5 on the mechanical properties of porous natural hydroxyapatite (NHA) derived from cortical bovine bones sintered at 1,050 degrees C is assessed. Hydroxyapatite (HA: Ca-10(PO4)(6)(OH)(2)) was synthesized using several methods and manufactured from natural materials such as coral or bone after removal of the organic matter by heating (noted NHA). The in vitro and in vivo studies showed that the natural apatite was well tolerated and has better osteoconductive properties than synthetic HA. Consequently, the NHA was manufactured from cortical bovine bone in all our studies. Nevertheless, its poor mechanical properties are one of the most serious obstacles for wider applications. So, P2O5 was added into NHA in order to enhance its initially poor mechanical strength. A careful combination between the main parameters controlling NHA elaboration such as milling techniques, compacting pressure, sintering temperature, and holding time may lead to an interesting NHA-based bioceramics. In this way, a vibratory multidirectional milling system using bimodal distribution of highly resistant ceramics has been used for obtaining submicron-sized NHA powders. To enhance the densification and lower the sintering temperature of porous NHA, different percentages of P2O5 (0.5-5.0wt%) were added into NHA powders. The porosity ratio ranged between 36 and 41%. Using this modified milling system, the best Vickers micro-hardness and the three-point bending strength values of powders sintered at 1,050 degrees C were 1GPa and about 46MPa, respectively. The latter value is significantly higher than that reported by other researchers (35MPa) using the sol-gel method.