Sol–gel derived fluor-hydroxyapatite biocoatings on zirconia substrate

Fluor-hydroxyapatite (FHA) film was coated on a zirconia (ZrO2) substrate by a sol–gel method. An appropriate amount of F ions was incorporated into the hydroxyapatite (HA) during the preparation of the sols. The apatite phase began to crystallize after heat treatment at 400°C, and increased in intensity above 500°C. No decomposition was detected by X-ray diffraction analyses up to 800°C, which illustrates the high thermal stability of the FHA films. The films showed a uniform and dense morphology with a thickness of 1 μm after a precisely controlled heat treatment process. These FHA films adhered firmly to the zirconia substrate, representing notable adhesion strengths of 70 MPa after heat treatment above 500°C. The dissolution rate of the FHA coating layer varied according to the heat treatment temperature, which was closely related to the film crystallinity. The dissolution rate of the FHA film was lower than that of the HA film, suggesting the possibility of a functional gradient coating of HA and FHA. The MG63 cells seeded onto the FHA films proliferated in a similar manner to those seeded onto pure HA ceramic and a plastic control.