Photocatalytic activity and antibacterial efficacy of UVA-treated titanium oxides

Studies have shown ultraviolet-A (UVA) irradiation of crystalline titanium oxides leads to the production of reactive oxygen species (ROS) via a photocatalytic process. The ROS exhibit antimicrobial properties that may be of benefit in preventing bacterial attachment to implant devices. Recent studies have suggested a potential benefit of mixed anatase and rutile oxides and dopants on the photocatalytic properties of titanium oxides. The goal of this work was to compare the photocatalytic activity of different anodized commercially pure titanium grade 4 (CPTi4) surfaces. CPTi4 specimens were anodized in three mixed-acid electrolytes to create crystalline oxide surfaces that were either primarily anatase, primarily rutile, or a combination of anatase and rutile. Additionally, the primarily anatase and combination oxides incorporated some phosphorous from the phosphoric acid component in the electrolyte. The photocatalytic activity of the anodized specimens was measured using both methylene blue (MB) degradation assay and comparing the attachment of S. aureus under irradiation with UVA light of differing intensities (1 mW/cm², 8 mW/cm², and 23 mW/cm²). Primarily rutile oxides exhibited significantly higher levels of MB degradation after exposure to 1 mW/cm² UVA lights. Primarily rutile specimens also had the largest reduction in bacterial attachment followed by the mixed phase specimens and the primarily anatase specimens at 1 mW/cm² UVA lights. Phosphorous-doped, mixed phase oxides exhibited an accelerated MB degradation response during exposure to 8 mW/cm² and 23 mW/cm² UVA lights. All anodized and unanodized CPTi4 groups revealed similar S. aureus attachment at the two higher UVA intensities. Although MB degradation assay and the bacteria attachment assay both confirmed photocatalytic activity of the oxides formed in this study, the results of the MB degradation assay did not accurately predict the oxides performance against S. aureus.