Adhesion Behavior of Escherichia coli on Plasma-Sprayed Zn and Ag Co-incorporated Calcium Silicate Coatings with Varying Surface Roughness

Our previous work demonstrated the good biocompatibility and bactericidal activity of a plasma-sprayed Zn and Ag co-incorporated calcium silicate ceramic coating (Ag-Ca₂ZnSi₂O₇), namely Ag-HT. In this work, we evaluated the influence of the surface roughness of Ag-HT coatings for Escherichia coli adhesion behavior, considering that surface topography is an important factor that regulates bacterial responses to biomaterials. Surface characteristics of as-sprayed and satin-finished Ag-HT coatings were investigated by scanning electron microscopy and measured using a surface roughness tester. Bacterial adhesion experiments showed that the number of viable E. coli cells on the as-sprayed or satin-finished coating surfaces was substantially lower than on the Ti-6Al-4V control surface, which can be explained by the antimicrobial effect of Ag and/or Zn. Moreover, the density of E. coli on the as-sprayed Ag-HT coating was considerably lower than on the satin-finished derivative. We attribute this difference to the fact that the as-sprayed coating surface was relatively smooth at a scale comparable to the size of an individual bacterium, while the satin-finished surface was slightly rough at this length scale and thus favored bacterial adhesion.