Properties of fluoridated hydroxyapatite–alumina biological composites densified with addition of CaF2

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] composites with 20 vol.% alumina (Al2O3) were sintered without pressure by adding CaF2. In the CaF2-free composites, severe decompositions occurred, resulting in poor densification. However, the addition of CaF2 suppressed the decomposition completely through the substitution of F− for OH− and consequent formation of fluor-hydroxyapatite [FHA, Ca10(PO4)6(OH)2−2xF2x]–Al2O3 composite. Hence, the obtained bodies reached full densification possessing enhanced mechanical properties. The hardness, flexural strength and fracture toughness of the CaF2-added composites improved by factors of ∼2–3 compared to CaF2-free composites, having values of 8 GPa, 125 MPa and 1.2 MPa m1/2, respectively. The osteoblast-like cells showed a similar proliferation behavior with respect to pure HA and plastic control for up to 7 days. The alkaline phosphatase (ALP) activity of the proliferated cells on the composites was higher than that on plastic control and slightly lower than that on pure HA, especially after prolonged culture periods.