| Abstract [eng] |
Healthcare-associated infections driven by resilient, spore-forming pathogens present a severe challenge for clinical sterilization protocols. Photocatalytic semiconductor coatings, particularly titanium dioxide (TiO2) doped with noble metals, offer a promising solution via the generation of reactive oxygen species (ROS) and localized antimicrobial effects, such as cytotoxic ion release. Analysis of the fabrication and microbial evaluation of anatase TiO2 thin films modified with silver nanoparticles (AgNPs) yielded critical flaws in current antimicrobial study methodology. TiO2 films were deposited using direct current (DC) magnetron sputtering and annealed to stabilize the anatase phase. Nanoparticle modification was achieved by depositing silver layers (5 nm, 7.5 nm and 10 nm) via radiofrequency (RF) magnetron sputtering, followed by solid-state dewetting at 400 °C. Surfaces were characterized using optical microscopy and water contact angle measurements. Antibacterial efficacy against B. subtilis was evaluated by adapting ISO 27447:2019 film cover method. Water contact angle measurements revealed highly hydrophilic films, from baseline 57.44° (TiO2) to approximately 1° (10 nm Ag). Microbiological testing yielded zero colony growth across all irradiated samples when using saline or 1/500 Nutrient Broth (NB) as washout liquid. The modified ISO 27447:2019 protocol did not take into consideration the production of EPS by bacteria. Methylene blue staining confirmed the presence of bacterial spores on the films post washing. XDLVO simulations demonstrated TiO2 and AgNP/TiO2 film interactions with B. subtilis bacteria. Investigations with TiO2 showed that anatase remains inert under both dark and UV conditions, while AgNP/TiO2 films showed a reduction in the bacterial population based on silver concentration. The simulation failed to consider biological factors of bacterial interactions, which overpower electrostatic interactions of TiO2 thin films. Bright-field and dark-field microscopy confirmed the degradation of AgNP/TiO2 film surface morphology post-experimentation. Mechanical forces required to detach EPS compounds compromise structural integrity, potentially leading to release of cytotoxic Ag+ ions into post-wash bacterial suspension. |
