Effect of surface chemistry and structure on bacterial adhesion on titanium dioxide materials with extreme wetting

Although it is widely believed that the antibacterial adhesion resistance of superhydrophobic surfaces stems from trapped air layers, the specific contributions of surface microstructure and trapped air layers in preventing bacterial adhesion remain unclear. In this study, four hydrophobic titanium dioxide (TiO₂) materials with different nanostructures were prepared, and ultrasonication was used to effectively remove trapped air, enabling a direct comparison of the hydrophobic materials with variations in surface morphology and trapped air. The results demonstrated that for the superhydrophilic samples, a large number of bacteria adhered to the surfaces, and no significant differences were observed among the various nanostructures. In sharp contrast, all four hydrophobic materials significantly reduced bacterial adhesion, with no significant differences observed among surfaces with different topographies. Millimeter scale, macroscopically visible air bubbles at the solid-liquid interphase greatly suppressed the bacterial adhesion, and the bubbles disappeared or decreased with the elapsed time. In contrast, invisible small bubbles (micrometer- or nanometer-scale) cannot decrease bacterial adhesion compared with the ultrasonicated sample (without trapped air). Therefore, the main reason for the significant reduction in bacterial adhesion on various hydrophobic surfaces is the fluorosilane surface modification. Air at the solid-liquid interface can only suppress the bacterial adhesion when it forms millimeter scale, visible bubbles. This work gives new ideas to the antibacterial application of superhydrophobic materials and is of great significance for the design of biomaterial surfaces with anti-adhesive properties.