Mechanical performance and osteoblast‐like cell responses of fluorine‐substituted hydroxyapatite and zirconia dense composite

A fluorine‐substituted hydroxyapatite (FHA) and zirconia (ZrO 2 ) dense composite (50:50 by volume) was fabricated, and its feasibility for hard tissue applications was investigated in terms of its mechanical properties and osteoblast‐like cell (MG63) responses in vitro . The incorporation of fluorine into the hydroxyapatite (HA) structure was highly effective in producing a completely dense apatite–ZrO 2 composite through a pressureless sintering route, by preventing the thermal degradation of the apatite and ZrO 2 . The resultant FHA–ZrO 2 dense composite had excellent mechanical properties, such as flexural strength (310 MPa), fracture toughness (3.4 MPam 1/2 ), hardness (10 GPa), and elastic modulus (160 GPa). The flexural strength and fracture toughness of the composite showed a noticeable improvement by a factor of ∼4 with respect to the pure apatites (HA and FHA). The MG63 cellular responses to the composite were assessed in terms of the cell proliferation (cell number and [ 3 H]‐thymidine incorporation) and differentiation (alkaline phosphatase activity, osteocalcin, and collagen production). The cells on the FHA–ZrO 2 composite spread and grew well, and proliferated actively during the culture period. The expression of alkaline phosphatase, osteocalcin, and collagen by the cells on the composite showed a similar trend to that on the pure apatites, although slight down‐regulations were observed, implying that the FHA–ZrO 2 50:50 composite retains the osteoblastic functionality and traits of the pure HA ceramics to a high degree. This finding, in conjunction with the considerable improvements in mechanical properties, supports the extended use of this composite for hard tissue applications. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res 72A: 258–268, 2005