Characterization and in vitro properties of anti-bacterial Ag-based bioceramic coatings formed on zirconium by micro arc oxidation and thermal evaporation

In this study, at the first step, the commercial pure zirconium (Zr) was coated by micro arc oxidation (MAO) technique in solution, consisting of calcium acetate and β-calcium glycerophosphate salt. Then, silver (Ag) thin film layer that had an average thickness of 20 nm was deposited on the MAO coated bioceramic surface by thermal evaporation (TE) technique. The phase structure, surface morphology, elemental composition and wettability of both Ag-coated and uncoated MAO coatings were characterized by powder-XRD and TF-XRD, SEM, EDX-mapping and contact angle goniometer, respectively. The powder and TF-XRD results indicated that cubic-zirconia, calcium zirconate and hydroxyapatite were detected on the surface after MAO and MAO + TE processes. Both coating surfaces were rough and porous. After TE process, Ag was homogeneously distributed on the surface. The Ag-based coated surface was hydrophobic compared to MAO surface. In vitro properties such as bioactivity and anti-bacterial tests of both coatings were investigated by soaking test in simulated body fluid (SBF) and bacterial formation, respectively. The apatite-forming abilities of both coatings were evaluated after soaking in SBF up to 10 days. After soaking process, secondary apatite layer formed on the Ag-based MAO coatings was more homogenous and denser than one on the MAO surface, whereas secondary apatite structure was completely formed on both surfaces. Therefore, the bioactivity of the Ag-based MAO surfaces was significantly improved compared to the uncoated MAO coatings under SBF conditions. For 10 Gram-positive and Gram-negative bacteria, the bacterial adhesion of the Ag-based MAO coatings was considerably reduced compared to plain MAO surface.