Effect of TiO2 doping on densification and mechanical properties of hydroxyapatite by microwave sintering

Abstract Hydroxyapatite (HAP) possesses excellent bioactivity/osteointegration properties. Nevertheless, its inferior flexural strength and fracture toughness limit its use in human weight-bearing parts. We investigated a microwave sintering technology which can be effectively used to develop titanium dioxide-hydroxyapatite (TiO2-HAP) ceramics with different amounts of TiO2 (0.8,1.6,2.4,3.2,4.0,4.8,5.6 and 6.4 wt%), which contribute to extremely high flexural strength (90–130 MPa) along with a good combination of elastic modulus and fracture toughness. The results of the Rietveld refinement show that multiphase bioceramics (HAP, β-TCP) can be achieved by doping nano-TiO2 under microwave sintering. Despite the fact that the main phases of the sintered TiO2-HAP ceramics are HAP and β-TCP, X-ray diffraction confirms the formation of the CaTiO3 and CaTi2O4(OH)2 phases. Furthermore, the sintering reactions to form these phases are discussed and the results show that an appropriate amount of nano-TiO2 can not only effectively inhibit the growth of grain, but also change the fracture mode and increase the relative density. Finally, it is found that doping nano-TiO2 by microwave heating is an effective technique for producing HAP/β-TCP composite load-bearing implants in clinical applications without coarsening the size of grain.