Influence of Silver Doping and Anodization Current Density on Aluminum Surface Properties and Surface Adhesion of Staphylococcus aureus and Escherichia coli

In this study, we investigated the influence of crystal structure, topography, and elemental composition of aluminum oxide surfaces on bacterial adhesion. The structural properties of the surfaces were systematically controlled by varying the current density (1.5, 2.0, and 2.5 A/dm2) and silver doping during the anodization process. The resulting changes in structural and morphological properties were examined by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), contact angle measurements, and profilometry. Using FE-SEM analysis, we evaluated the adhesion of model bacteria, Escherichia coli and Staphylococcus aureus, to surfaces exhibiting diverse morphologies and elemental compositions. The surface roughness and crystal size of the aluminum oxide increased proportionally with the applied current density and silver doping. According to the XRD results, the slip plane crystal structure of (311) increased proportionally to the current density but decreased with silver doping. Specifically, while stepped atomic alignment of (311) planes facilitates bacterial attachment, smoother (200) planes reduce the adhered bacteria population. Further analysis via XPS revealed that the oxide crystal structure of undoped surfaces shifted from the tetrahedral to octahedral form with increasing current density, while silver-doped surfaces exhibited the opposite trend. Additionally, increasing current density during the preparation of silver-doped surfaces diminished the ratio of ionic silver to metallic silver, suggesting a lowered propensity for bacterial adhesion. S. aureus adhesion to undoped surfaces increased 4.46-fold for surfaces prepared at 2.5 A/dm2 compared to that at 1.5 A/dm2. Moreover, E. coli adhesion was completely inhibited on silver-doped surfaces anodized at 1.5 A/dm2. Reducing the surface roughness and incorporating silver during the anodization of aluminum surfaces decrease the number of bacteria adhering to aluminum oxide surfaces.