Microstructure and material properties of porous hydroxyapatite-zirconia nanocomposites using polymethyl methacrylate powders

Bone like porous monolithic hydroxyapatite (HAp) and hydroxyapatite-zirconia (HAp-ZrO2) nanocomposites were fabricated by a pressureless sintering process with polymethyl methacrylate (PMMA) powders as the pore forming agent. It was found that such powders could be successfully removed by a burning-out process, leaving the sintered body with randomly distributed pores. The material properties, i.e., the pore morphology, compressive strength and elastic modulus, could be changed dramatically by increasing the pore forming agent. With 50 vol.% of the agent, both the porous monolithic HAp and HAp-ZrO2 nanocomposites formed interconnected porous microstructures. The compressive strengths of porous monolithic HAp and HAp-ZrO2 nanocomposites were about 31.4 and 34.9 MPa, respectively. Their elastic moduli were about 19.6 GPa and 23.4 GPa, respectively, which are almost the same as those of the human cortical bones. Porous HAp-ZrO2 nanocomposites exhibited better compressive strengths and elastic moduli than that of porous monolithic HAp bodies due to the strengthening effect of high strength and toughened reinforcing bio-inert ZrO2 nano-particles.