Durability of photocatalytic ZnO-based surface coatings and preservation of their antibacterial effect after simulated wear

This study focused on antibacterial durability testing of surface coatings based on acrylic matrix-embedded UVA-activated ZnO. Such coatings on stainless steel were treated by dry rubbing, wet rubbing, and abrasive treatment to simulate wearing during everyday touching, cleaning, and aggressive scrubbing. Abrasive treatment caused clear topological changes to the surfaces, flattened the surface at the micrometer scale, and released a significant amount of surface material, which was partly acrylic matrix and partly the embedded ZnO. The highest release of Zn, the most prominent photocatalytic activity under UVA and the greatest antibacterial effect, was observed for abrasively treated surfaces. Although a small amount of surface material was released from surfaces after dry and wet rubbing, no significant increase in Zn release or photocatalytic activity was detected. On the contrary, antibacterial activity after those treatments decreased in comparison with untreated surfaces, likely due to partial surface masking by the released acrylic matrix. In summary, our results indicate that antimicrobial ZnO material immobilized in acrylic matrix creates stable surface coatings that may lose some of their efficacy during daily use and cleaning procedures, but activity of which will be retained during a more aggressive abrasion procedure.