Preparation of graded zirconia–CaP composite and studies of its effects on rat osteoblast cells in vitro

Hydroxyapatite (HAP) has excellent biocompatibility and bone bonding ability, but it is mechanically weak and brittle. To overcome this problem, we prepared a graded composite with calcium phosphide (CaP, decomposed from HAP during sintering) coating on the surface of zirconia (ZrO2) ceramics. The mechanical properties and microstructure characteristics were studied with various techniques. The biocompatibility of graded ZrO2–CaP composite was examined with rat osteoblast cells (OB cells) in vitro. Its effects on the production of alkaline phosphatase (ALP), Interleukin-6 (IL-6) and Growth-transforming Factor-β (TGF-β) by the OB cells were measured. The results showed that the mean tensile strength of the graded ZrO2–CaP composites was 17.8 MPa, the maximum bending strength was 1112.24 MPa, and KIC was 7.3–11.4 MPa·m1/2, indicating that the composite was physically strong for use as an implant material. The ALP activity, IL-6 and TGF-β concentrations of the graded composite treated OB cells were much higher than that of the pure ZrO2 treated group. There was no significant difference in ALP activity, the IL-6 and TGF-β concentrations between the graded ZrO2–CaP composite group and HAP. The cytotoxicity of the composite material to rat fibroblast cells was insignificant. The graded zirconia–CaP composite greatly facilitated the proliferation and differentiation of rat OB cells in vitro, demonstrating excellent biocompatibility.