Fabrication and in vitro properties of zinc-based superhydrophilic bioceramic coatings on zirconium

In this study, as the first step, the bioceramic coatings were fabricated on Zr (commercial pure zirconium) in calcium acetate and β‑calcium glycerophosphate salt-based electrolyte by MAO (micro arc oxidation). And then, as the second step, the Zn (zinc) thin film layer measured an average thickness of 5 nm was coated on the MAO surface by TE (thermal evaporation). The phase composition, surface and cross sectional morphology, elemental composition and wettability of the MAO and Zn-based MAO coatings were analyzed by powder-XRD and TF-XRD, SEM, EDS-mapping and contact angle goniometer, respectively. The phases of cubic-ZrO2, perovskite-CaZrO3 and HA (hydroxyapatite) were observed on the surfaces by powder and TF-XRD analyses. The morphology of the MAO surface was not changed by TE although the chemistry of it was different from the MAO surface. The surfaces of both coatings were porous and rough. The Zn was uniformly deposited through the whole surface. After TE process, the wettability of the surface decreased and the Zn-based surface exhibited superhydrophilicity compared to MAO surface. In vitro bioactivity test of both coatings were investigated by immersion test in SBF (simulated body fluid) up to 10 days. The bone like apatite layer (secondary apatite) on the Zn-based bioceramic surface was compact and uniform compared the one on the MAO surface although it was completely propagated through both surfaces. In vitro anti-bacterial test of both coatings were carried out by microbial adhesion for Gram positive and Gram negative bacteria. It was observed that the microbial adhesions of the Zn-based bioceramic surfaces were lower than ones of the MAO bioceramic surfaces for all Gram-positive and Gram-negative bacteria.