Preparation of hydroxyapatite‐titania hybrid coatings on titanium alloy

Abstract Hydroxypapatite‐titania hybrid films on Ti6Al4V alloys were prepared by sol–gel technique by incorporating presynthesized hydroxypapatite (Ca₁₀(PO₄)₆(OH)₂ or HAp) powders into a titanium‐alkoxide dip coating solution. Titania network was formed by the hydrolysis and condensation of Ti‐isopropoxide Ti[OCH(CH₃)₂]₄‐based sols. The effect of titania sol formulation, specifically the effect of organic solvents on the microstructure of the dip coated films calcined at 500°C has been investigated. The coatings exhibit higher tendency for cracking when a high vapor pressure solvent, such as ethanol (C₂H₅OH) is used causing development of higher macroscopic stresses during evaporation of the sol. Titania sol formulations replacing the solvent with n‐proponal (CH₃(CH₂)₂OH) and acetly‐acetone (C₅H₈O) combinations enhanced the microstructural integrity of the coating during evaporation and calcination treatments. Sol–gel processing parameters, such as multilayer coating application and withdrawal rate, can be employed to change the titania thickness in the range of 0.120–1.1 μm and to control the microstructure of HAp‐titania hybrid coatings. A high‐calcination temperature in the range of 400–600°C does not cause a distinct change in crystals nature of the titania matrix or HAp, but results in more cracking due to the combined effect of densification originated stresses and thermal stresses upon cooling. Slower withdraw rates and multilayer dip coating lead to coatings more vulnerable to microcracking. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009