In vitro apatite formation on surface-modified titanium coatings prepared by reactive plasma spraying

In vitro nucleation of apatite was studied over surface-modified Ti coatings prepared by reactive plasma spraying (RPS). An in-situ surface-modification of Ti particles is conducted by making use of plasma-enhanced reactions between the Ti particles and the reactive gaseous species in the plasma flame during plasma spraying. Surface-modified Ti coatings were deposited on Ti substrates by radio-frequency (rf)-RPS using a thermal plasma of At gas containing 1-6% N-2 and/or 1-6% 02 at an input power of 16 kW. As a means of surface modification, Ti powders impregnated with 0.05-0.2 mol% Ca were also sprayed. Compositional changes in the coatings' surface after soaking in simulated body fluid (SBF) were examined by Fourier transform infrared spectroscopy (FT-IR) and thin film X-ray diffraction (TF-XRD). The Ti coatings prepared with Ar-O-2 and Ar-N-2-O-2 plasma formed apatite after 3 days of soaking in SBF. On the other hand, no Compositional change was observed in the surface of the Ti coatings sprayed with Ar-N-2 plasma, even after 7 days of soaking in SBF. In SBF tests, we observed a retardation of apatite deposition for the Ca-added Ti coatings prepared with Ar-O-2 and Ar-N-2-O-2 plasmas. Analyses by X-ray photoelectron spectroscopy indicated that the Ca impregnated in the R-PS-Ti coatings formed a Ca-O compound.