Researchers from the Institute of Physics and the Institute of Molecular and Cell Biology of the University of Tartu have shown in a recently published study that antibacterial coatings which initially appear highly effective at destroying bacteria, may lose their performance over time. Therefore, long-term testing is essential for developing the best antibacterial materials.
Contamination of frequently touched surfaces with bacteria and other microorganisms is a major source of infectious disease outbreaks. Studies suggest that 40% of hospital-acquired infections may be spread specifically through contaminated surfaces. Therefore, coating these surfaces with light-activated, or photocatalytic, antibacterial coatings is a promising solution to reduce the spread of disease-causing bacteria.
Such coatings generate reactive oxygen species that destroy bacteria under exposure to UV-A radiation, which makes up most of the sunlight. Unfortunately, the properties of photocatalytic coatings change over time, and their beneficial effect diminishes.
Overactive TiO 2
The aim of the researchers' study was to determine the long-term effect of UV-A radiation on acrylic-based surface coatings that contained photocatalytic titanium dioxide (TiO2) and zinc oxide (ZnO) particles capable of destroying bacteria. To do this, the coating was applied to a steel surface and was exposed for nine weeks in conditions resembling everyday life with high humidity but with much more intense UV-A radiation.
The results showed that although TiO2 nanoparticles do produce antibacterial reactive oxygen species under UV‑A radiation, an undesirable side effect emerged within three weeks: these reactive species also degrade the acrylic‑based coating itself. As the coating breaks down, the nanoparticles are lost, causing the beneficial antibacterial effect to fade.
However, ZnO particles with similar antibacterial properties did not significantly degrade the lacquer – the coating remained intact and its antibacterial properties persisted even after prolonged exposure to UV-A light.
According to the researchers, this striking difference between the two antibacterial materials was surprising, as the photocatalytic antibacterial performance of the ZnO‑based coatings had initially been better than that of the TiO2‑based materials.
Need for long ‑ term testing
According to the researchers, the development of new antibacterial coatings should always consider the full picture. Therefore, long‑term experiments are indispensable alongside short‑term tests.
The article describing the results of the study, „Artificial aging induced changes in ZnO- and TiO₂-based polyacrylic surface coatings“ , was published in the journal npj Materials Degradation , and its open‑access publication was supported by the University of Tartu.
The authors of the study are Mati Kook, Celeste Peterson, Aadil Shafi Bhat, Alexandra Nefedova, Alexander Vanetsev, Angela Ivask and Vambola Kisand.
npj Materials Degradation
Experimental study
Not applicable
Artificial aging induced changes in ZnO- and TiO₂-based polyacrylic surface coatings
17-Jan-2026
There is no conflict of interest