Antimicrobial and self-cleaning wall paints

Antimicrobial and self-cleaning wall paints that provide antiviral surfaces have been developed in a new research project. The effect of the coatings is unlimited in time and not harmful to the environment.

Virologists agree: the next pandemic will come. The only question is when. Antimicrobial wall paints and coatings could reduce the risk of infection in hospitals and public facilities. But so far they have two serious disadvantages: On the one hand, their effect fades after a certain amount of time. The surfaces constantly release so-called active substances. These are metallic ions, silver nanoparticles or organic substances that attack and kill viruses. But at some point, the reservoirs are empty and all the active substances are used up. The surface loses its antimicrobial properties.

On the other hand, antimicrobial surfaces release their active substances into the environment. Silver ions and silver nanoparticles in particular can damage the microbiome in the soil, algae and other living organisms in and around water.

A research team led by Christina Bauder from the Fraunhofer Institute for Manufacturing Engineering and Automation IPA has now succeeded in developing antimicrobial wall paints that are permanently effective and do not release any substances into the environment. "For an unlimited antimicrobial effect, the active substance itself must not be involved in a chemical reaction and be consumed in the process," says Bauder, head of the Paint Chemical Application Technology research team at Fraunhofer IPA. The researcher therefore relies on so-called photocatalysis, i.e. a chemical chain reaction that never ends when exposed to light and can be repeated an infinite number of times.

Photocatalysis is triggered by sunlight or an artificial light source. It can therefore also take place under indoor lighting. The light puts the semiconductor titanium dioxide into an excited state. The titanium dioxide transfers the light energy it receives to water and oxygen molecules in the air. They react to form unstable radicals. On contact with viruses, these radicals react with their outer skin and destroy them in the process. The viruses die. In the dark, photocatalysis gradually comes to a standstill. The previously so active titanium dioxide reverts to its original inactive state - until the chain reaction is restarted by light.

In field tests, Bauder's research team painted walls in two clinics and a kindergarten with their newly developed antimicrobial paints. At regular intervals, the researchers took samples from the walls with swabs and cultivated them on a culture medium in a Petri dish. No germs were detectable in the laboratory.

However, it is not only viruses that fall victim to photocatalysis, but also dirt particles. In studies, test strips of wall paint were contaminated with blood, red wine, mustard, coffee and black shoe polish. After five or 30 minutes of exposure, most of the stains could be removed with a single wipe and left hardly any residue. After a week, most of the stains had either disappeared by themselves or were barely visible.

The antimicrobial wall paints were developed by the project team, which also included employees from Griwecolor in Döggingen and IBT Deutschland in Baienfurt, as part of the research project "Interior coatings with antiviral effect through the use of photocatalytically active coatings with high long-term durability that can be activated in the visible area" (InVisiBL). The Dr. Michael Lohmeyer Microbiology Laboratory in Münster has developed procedures to investigate their antiviral and antimicrobial effect and confirmed the effectiveness of the new coating. The field tests were carried out at the St. Marien Catholic kindergarten in Döggingen, the Oberschwabenklinik in Ravensburg and the Graubünden Cantonal Hospital in Chur.

The InVisiBL research project was supported by the Invest BW funding program of the Baden-Württemberg Ministry of Economic Affairs, Labour and Tourism. (OM-9/24)