Fabrication, characterization and in vitro properties of silver-incorporated TiO2 coatings on titanium by thermal evaporation and micro-arc oxidation

In this study, as a first step, a silver (Ag) thin film layer was deposited on cp-Ti (Grade-2) by thermal evaporation-physical vapor deposition (TE-PVD). And then, Ag-based titanium surface was coated by micro-arc oxidation (MAO) in solution, consisting of sodium silicate and potassium hydroxide at the second step. The phase structure, surface morphology, elemental composition, functional groups, wettability and surface topography of both coatings were characterized by XRD, SEM, EDS-mapping, contact angle goniometer, ATR-FTIR and surface profilometer, respectively. The XRD results indicated that anatase and rutile were detected on the surface after MAO and TE + MAO. Both coatings' surfaces were rough and porous due to the existence of plasma chemical reactions on micro discharge channels. The Ag-incorporated MAO coating exhibited much more hydrophilic character than MAO coating. The Ag was homogeneously distributed through the surface. The biological properties such as bioactivity and anti-bacterial tests of the coatings were analyzed by immersion test in SBF and bacterial formation. The apatite-forming abilities of both coatings were evaluated by soaking in simulated body fluid (SBF) up to 28 days. After soaking, apatite structure was formed on the MAO and Ag-incorporated MAO surfaces and the bioactivity of MAO surface on Ti was considerably improved compared to the MAO surface under SBF conditions. The homogenous and dense apatite distribution was observed on Ag-incorporated MAO coatings. The bacterial adhesion of Ag-incorporated MAO coatings was significantly reduced compared to plain MAO surface.