Surface and in vitro properties of Ag-deposited antibacterial and bioactive coatings on AZ31 Mg alloy

Abstract Ag (silver)-based bioceramic coatings were fabricated on AZ31 Mg alloy by combining the MAO (micro-arc oxidation) and PVD (physical vapor deposition) methods. As a first step, AZ31 Mg surfaces were coated using MAO using a solution consisting of sodium silicate and potassium hydroxide. As a second step, an Ag layer was accumulated on the MAO surfaces using the PVD method. The XRD patterns thus obtained demonstrated the presences of Mg (magnesium), Si (silicon), M2SiO4 (forsterite) and MgO (periclase) on the Ag-deposited MAO surfaces. The elemental or compound structures of Ag were not detected due to the homogeneous distribution of a trace amount of Ag on the surfaces. Both coatings' surfaces were porous due to the existence of discharge channels. All elements were found to be uniformly distributed across the entirety of the surfaces. The Ag-deposited MAO surfaces were found to have hydrophobic properties with respect to plain MAO surfaces. Newly formed layers consisted of Ca 15 (SiO 4 ) 6 (PO 4 ) 2 (calcium silicate phosphate), Ca 3 (PO 4 ) 2 (tuite) and Ca 10 (PO 4 ) 6 (OH) 2 (hydroxyapatite) as produced on plain MAO and Ag-deposited MAO surfaces by immersion in SBF (simulated body fluid); these layers were more homogeneous on Ag-deposited MAO coatings than ones on plain MAO. Also, for E . coli ( Escherichia coli ) and S . aureus ( Staphylococcus aureus ) bacteria, the numbers of active bacterial colonies on Ag-deposited MAO surfaces were significantly reduced with respect to plain MAO surfaces.