Coating and characterization of thin hydroxyapatite coatings on titanyium by sol-gel and biomimetic coating technique

In this study hydroxyapatite (HA) was coated on the titanium surfaces which is prepared by acid passivation technique and hydrogen sputtering technique by sol-gel and biomimetic techniques and characterization of coating was performed. Improvement of HA film adhesion increased the bond formation between implant bone interface and allows fast bone ingrowths. Titanium surfaces were passivated by acid solution and threaded by hydrogen sputter at 300 oC for 1 hour. Ca(NO3)2.4H2O and NH4H2PO4 were chosen as starting precursors for Ca and P source. NH4OH was used for sol stabilization and pH adjustment. Simulated body fluids with different concentrations (1.5, 10XSBF) were prepared for HA coating by biomimetic method. HA coatings on titanium surface which were produced by sol-gel method was sintered at temperatures between 750 and 900 oC under normal atmosphere. Structural, morphological and surface chemistry characterization were done by using XRD,SEM,XPS, AFM, FTIR AND DSC/TG analysis techniques. Nano indentation and scratch tests were used for the determination of the elastic modulus of the coatings which produced by sol-gel technique. Corrosion behaviour of the implant was determined by Gamry Referance 600 potentiometer/galvanometer. As result of the experimental studies, it was found that; adhesion strength of the coatings to the implant surface was increased when hydrogen sputtering applied to titanium surfaces. Presence of TiO2 layer between titanium and HA interface increased the adhesion of the coating applied by sol-gel technique. In addition it was seen that TiO2 layer play a barrier role against corrosion. Depending on the dipping time and process cracks and weak coatings were obtained at thick coatings. For this reason corrosive effect was reduced. Certain coating thickness increased the barrier potentials (Eb). Current values was measured as 900 nA for the uncoated samples whereas 20-30 nA values were measured for HA coated samples. HA coated samples allowed 90% better corrosion protection behaviour than uncoated titanium samples.