Influence of oxygen content on the antibacterial effect of Ag-O coatings deposited by magnetron sputtering

Ag and AgOx thin films were deposited by pulsed DC magnetron sputtering, for medical devices, in order to provide antibacterial properties. During the deposition process, oxygen flow, and, consequently, oxygen fraction, was varied (0-15 sccm) to understand the influence of oxygen species in the physical, chemical and structural properties of thin films. Coatings morphology was observed by scanning electron microscopy (SEM) and their nanostructure and composition were assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. XRD and XPS analyses revealed that Ag thin films are composed by metallic Ag, which crystallizes in fcc-Ag phase; whereas AgOx showed a mixture of Ag2O and AgO phases for low oxygen fraction that became single AgO with the increase of oxygen fraction in the discharge. Surface wettability and surface tension of the coatings were also determined showing hydrophobic character. Halo inhibition zone tests were performed against Staphylococcus epidermidis, in order to evaluate the antibacterial behavior of coatings, and silver ion release was measured. Only AgOx presented antibacterial behavior, showing that the presence of silver oxide are the main reasons for the antibacterial effect, probably due to the increased production of ROS (Reactive Oxygen Species), making these coatings promising for medical applications. (C) 2016 Elsevier B.V. All rights reserved.