Evaluation of the in-vitro behavior of nanostructured hydroxyapatite and zinc doped hydroxyapatite coatings obtained using solution precursor plasma spraying

The in-vitro behavior of hydroxyapatite (HA) and zinc (Zn) doped HA coatings obtained using solution precursor plasma spraying is evaluated in this work. The modifications of the surface morphology and phase composition of the coatings after immersion in simulated body fluid (SBF) were analyzed. In particular, apatite layer was formed on the pure HA coating's surface and inside their micropores. The layer exhibited needle-like nanostructures where needles had diameter of 7-10 nm. The formation of apatite was explained by the surface charge mechanism. The formed thin apatite layer is considered to be bone-like apatite based from the thin film-X-ray diffraction analysis. The nanometric/submicrometric deposits of the HA coatings resulted to greater effective surface area exposed to SBF which allows for the accelerated formation of homogeneous apatite layer. Moreover, apatite was not formed in all Zn doped HA coatings due to the inhibiting effect of Zn ions present at the coatings' surface. This observation helped understand the mechanism of apatite formation based on the exchange of ionic charges between the SBF and the surface of the HA coating. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2101-2108, 2018.