Mechanical properties and apatite forming ability of TiO2 nanoparticles/high density polyethylene composite: Effect of filler content.

Composite materials consisting of TiO(2) nanoparticles and high-density polyethylene (HDPE), designated hereafter as TiO(2)/HDPE, were prepared by a kneading and forming process. The effect of TiO(2) content on the mechanical properties and apatite forming ability of these materials was studied. Increased TiO(2) content resulted in an increase in bending strength, yield strength, Young's modulus and compressive strength (bending strength = 68 MPa, yield strength = 54 MPa, Young's modulus = 7 GPa, and compressive strength = 82 MPa) at 50 vol% TiO(2). The composite with 50 vol% TiO(2) shows a similar strength and Young's modulus to human cortical bone. The TiO(2)/HDPE composites with different TiO(2) contents were soaked at 36.5 degrees C for up to 14 days in a simulated body fluid (SBF) whose ion concentrations were nearly equal to those of human blood plasma. The apatite forming ability, which is indicative of bioactivity, increased with TiO(2) content. Little apatite formation was observed for the TiO(2)/HDPE composite with 20 vol% content. However, in the case of 40 vol% TiO(2) content and higher, the apatite layers were formed on the surface of the composites within 7 days. The most potent TiO(2) content for a bone-repairing material was 50 vol%, judging from the mechanical and biological results. This kind of bioactive material with similar mechanical properties to human cortical bone is expected to be useful as a load bearing bone substitute in areas such as the vertebra and cranium.