Surface Activation of NiTi Alloy by Using Electrochemical Process for Biomimetic Deposition of Hydroxyapatite Coating (TECHNICAL NOTE)

Electrochemical depositions of calcium phosphate (Ca-P) film on NiTi alloy in concentrated simulated body flood (SBF×5) were carried out by cathodic polarization. The Ca-P layer was successfully deposited on Ni-Ti alloy substrate under 10mA/cm2 current density for 2 hours at room temperature. Then, in order to investigate the bioactivity of the pre-calcified samples, they were immersed in SBF for 1 and 3 days. The microstructure, composition and bioactivity of the coatings were evaluated by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. Results showed that the activation of the surface of the NiTi alloy by electrochemical process can significantly enhance the biomimetic deposition during time. On the other hand, by increasing immersion time of pre-calcified samples in SBF from 1 to 3 days, the biomimetic coating uniformly covered the surface of the sample. The ratio of the Ca/P for the pre-calcified sample after immersion in SBF for 3 days was about 1.5 which is very close to the Ca/P ratio of stoichiometric hydroxyapatite.