In situ formation of bioactive titanium coating using reactive plasma spraying

Abstract

In vitro nucleation of apatite was studied on surface-modified Ti coatings prepared by reactive plasma spraying (RPS). The in situ surface modification of Ti particles was conducted by making use of plasma-enhanced reactions between the Ti particles and the reactive gaseous species in the plasma flame during RPS. Surface-modified Ti coatings were deposited on Ti substrates by rf-RPS using a thermal plasma of Ar gas containing 1%–6% N2 and/or 1%–6% O2. As a means of surface modification, Ti powders impregnated with 0.05–0.2mol% Ca were also sprayed. Compositional changes in the coatings’ surface after soaking in simulated body fluid (SBF) were evaluated by Fourier transform infrared spectroscopy and thin-film x-ray diffraction analyses (TF-XRD). The Ti coatings prepared with Ar-O2 and Ar-N2-O2 plasma formed bone-like apatite after three days of soaking in SBF. On the other hand, no compositional change was observed in the surface of the Ti coatings sprayed with Ar-N2 plasma, even after seven days of soaking in SBF. In the TF-XRD patterns for the Ti coatings sprayed with oxygen-containing plasma, TiO2 (anatase and rutile phase) were commonly observed. In SBF tests, we observed a retardation of apatite deposition for the Ca-added Ti coatings prepared with Ar-O2 and Ar-N2-O2 plasmas. Analyses by x-ray photoelectron spectroscopy indicated that the Ca impregnated in the RPS-Ti coatings formed a Ca-O compound.