Hydroxyapatite coating on NiTi shape memory alloy by electrophoretic deposition process

In this study, natural hydroxyapatite has been electrophoretically deposited on NiTi shape memory alloy. The hydroxyapatite powder was characterized using transmission electron microscopy, X-ray diffraction and also particle size measurement. A stable suspension was prepared by adding 80 g/l natural hydroxyapatite powder to n-butanol and stabilized using triethylenamine as a dispersant and binder. Electrophoretic deposition was executed on a cathode at a constant voltage, namely at 40, 60 and 80 V in 120 s. After deposition, samples were dried at room temperature for 24 h then the coated samples were sintered at 800 degrees C for 2 h under argon atmosphere. It was illustrated that the sample coated at 60 V has a continuous and dense surface. Scanning electron microscope and X-ray diffraction analysis were used to investigate the microstructure and phase purity of hydroxyapatite coating. The release of Ni ions from coated samples in simulated body fluid was studied and results revealed that the performance of the sample coated at 60 V as a barrier against the release of Ni ions is more effective than samples coated at 40 and 80 V. Also, the bonding strength of the hydroxyapatite film coated at 60 V was found to be 18.1 +/- 3.2 MPa. The bioactive behavior of hydroxyapatite coatings was investigated by immersion in simulated body fluid for 7 days. As expected, hydroxyapatite crystals formed on the surface of the coated samples which confirms the bioactivity of the surface. (c) 2012 Elsevier B.V. All rights reserved.