XPS study on potential suppression factors of suppressing in vitro apatite formation on anatase films prepared on various substrates

Multilayer anatase films were coated by sol–gel technology on various substrates such as stainless-steel, alumina, and glass, respectively. Their in vitro apatite-forming ability was examined by immersion in Kokuboʹs simulated body fluid (SBF; pH 7.4, 36.5 °C). Although on anatase layer on alkali-free glass apatite was deposited within 7 d, no apatite was found on anatase deposited onto stainless steel, alumina or glass substrates within 7 d to prove they were bioinert. X-ray photoelectron spectroscopy was able to detect chromium, aluminum, or sodium on the surface of the anatase films. This indicated that these ions possibly inhibited the in vitro apatite-forming ability.