Sintering behavior, mechanical properties, and biocompatibility of TiO₂–Co-calcium phosphates composites prepared by AROS process

TiO₂–Co–hydroxyapatite (TCN–HA) powders, in which TCN prepared by an alloying–recomposition–oxidation–sintering process was mixed with HA (5–40 vol%), were sintered at 1100, 1200, 1300, and 1400 °C. Structural characterization was performed using X-ray diffraction, field-emission scanning electron microscopy, and energy-dispersive spectroscopy. The relative density (RD) of the sintered TCN–20HA increased until 1200 °C, followed by a rapid decrease at temperatures higher than 1300 °C. The density decrease at higher temperatures was related to the release of a large amount of H₂O by the decomposition of hydroxyapatite (HA). The flexural strengths and fracture toughness of the TCN–HA samples with HA contents up to 20 vol% and Vickers hardness of all of the samples were higher than those of the pure TCN sample. The enhancements in their mechanical properties could be attributed to the higher densification. In a cytotoxicity test, the viabilities of cells cultured for 2 days on the TCN–HA samples were significantly increased for HA contents up to 20 vol% (p < 0.05). In addition, all of the samples with HA exhibited increased viabilities of cells cultured for 4 days. Therefore, the HA addition is effective for the enhancements in their mechanical properties and cell viability and proliferation with the culture time.