The sintering and mechanical behavior of hydroxyapatite with bioglass additions

There is increasing interest in the potential of composites of hydroxyapatite with phosphate- or silicate-based bioactive glasses, and certain of these glass additions have been found, in previous work, to aid densification and form a mechanically-reinforced, bioactive material; in particular, large improvements in flexural strength and fracture toughness were obtained through the addition of small amounts of phosphate glass. Less is known about the mechanical behavior of HA/bioglass composites, although in vivo studies by other workers have shown encouraging biological results. In this investigation, the sintering behavior, mechanical properties, and microstructure of composites of HA with up to 50 wt % glass, were analyzed. X-ray diffraction showed the phase composition of sintered composites with up to 5 wt % added bioglass to be non-stoichiometric HA with alpha-TCP or beta-TCP. Phase analysis of composites containing higher glass additions was impracticable due to peak broadening and overlap, although reaction products, at the highest glass additions and sintering temperatures, may include wollastonite-2M and beta-Na2Ca4(PO4)2SiO4. Sintered density, and mechanical properties other than fracture toughness, showed no significant improvement over HA.