Sol–gel derived hydroxyapatite coatings on titanium substrates

The oscillatory micromovements at the interface between the implant and the bone induce fretting wear and sometimes, fatigue cracks, causing early failure of the joint prosthesis. Hydroxyapatite films were formed using a sol–gel method from an organic precursor solution. The average film thickness was found to be 1.0 μm. Composite coatings containing HA doped with ZrO2 were also formed. Hydroxyapatite (HA) and composite films of HA and ZrO2 formed on commercial titanium substrates using an organic precursor solution by sol–gel route, were tested for fretting wear using a ball-on-flat fretting apparatus. The moderately lower values of the coefficient of friction (0.4–0.5) and morphology of the wear pits for considerably long cycles of fretting indicate strong bonding of the HA coating to the titanium surface. The interface shear strength of a thin hydroxyapatite film on commercial purity titanium has been evaluated using a substrate straining method. The maximum interfacial strength was about 570 and 678 MPa, for the pure HA and composite films, respectively, on the highly polished surface. However, the maximum interfacial strength was found to be about 263 MPa on the oxidized surface.