Every year, around four million people in Europe contract infections caused by hospital germs [1]. Pathogens spread via surfaces such as handrails, handles or touchscreens. The EU-funded joint project SanFlex is researching a photocatalytic coating that is (additionally) equipped with super-acidic surface properties.
The innovative coating prevents pathogens from adhering and also kills microorganisms. The specific aim of the SanFlex research project is to develop suitable coating technologies for the cost-effective production of antipathogenic protective films for touchscreens.
Surfaces slow down pathogens
With the onset of the colder season, infectious diseases and flu epidemics are on the rise again. Surfaces such as handrails, handles and touchscreens as well as other highly frequented surfaces harbor the risk of transmitting pathogens. This is particularly serious in healthcare facilities, where a large number of infected people come together. In Europe, around 4 million infections caused by hospital germs are recorded every year, 600,000 of them in Germany alone [1,2]. In order to reduce the spread of these germs, surfaces with antimicrobial properties can make a significant contribution to curbing the transmission of pathogens.
Titanium oxide miracle layer
Example of a microbially contaminated surface (Photo: Fraunhofer FEP, Daniel Mählich)Titanium oxide coatings, especially crystalline titanium dioxide (TiO2), are known for their antimicrobial and self-cleaning surface properties. The Fraunhofer FEP in Dresden has been researching and realizing coating systems and the associated coating processes for transfer to industrial production for many years. In addition to coatings on rigid substrates such as glass, the institute's scientists also develop surface coatings and their functionalization for flexible materials such as films and ultra-thin glass. As part of the EU research project SanFlex, a Swedish-German consortium is now working on new coating technologies to effectively reduce pathogens on surfaces. To this end, the team is developing a new type of titanium oxide coating that is modified to form super-acidic surfaces. The project is being funded as part of the European Union's Horizon 2020 research and innovation program. Saxony is also providing financial support for the research project.
Doubly effective antipathogenic coating
The superacidic surface properties are generated by a photofixation process, while the photocatalytic properties of the titanium oxide layers remain unaffected. This super-acidic coating has oleophobic and catalytic properties that prevent grease and pathogens from adhering to the surface. The coating acts as an antipathogenic protection that combines two properties in one product: the adhesion of pathogens is initially prevented and at the same time microorganisms on the surface are killed.
Researchers are pursuing two approaches
Nanocrystalline structures are required to bind the inorganic acid groups to the titanium oxide layers. The formation of such crystalline structures in titanium oxide layers usually requires process temperatures of at least 250 °C, which are problematic for flexible materials such as polymer films. The project is therefore investigating various process approaches that enable the production of crystalline layers at lower substrate temperatures. At Uppsala University in Sweden, high-power impulse magnetron sputtering (HiPIMS) is one of the methods used to achieve the desired crystallinity of the layers.
Titanium dioxide thin film crystallized by FLA on temperature-stable polymer. The graphic shows the XRD measurement of the anatase phase (Photo: Fraunhofer FEP)Fraunhofer FEP is pursuing another approach, as project manager Dr. Matthias Fahland explains: "We are using flash lamp annealing (FLA) as a further method for producing the crystalline structure of the previously sputtered - still amorphous - TiO2 layers at room temperature. We have already been able to demonstrate the basic production of crystalline layers using this method on rigid substrates such as glass and also on flexible ultra-thin glass. With our laboratory and pilot systems, we are able to reproducibly produce and scale up these layers. These initial successes not only take us further in the area of building equipment, but can also enable improved hygiene in public and medical facilities in the future."
Efficient and economical production possible
The results were achieved on glass substrates with an area of at least 50 × 50 mm2 in laboratory facilities and in the ILA 900 pilot production facility at Fraunhofer FEP. The latter can process coatings on an industrial scale and has additional equipment to not only treat rigid glass substrates, but also to process flexible thin glass in substrate sizes of up to 600 × 1200 mm2 without shading. The post-treatment process of the FLA is also scalable to this treatment area. A central goal of the SanFlex project is to adapt the processes for coating flexible substrates for the production of prototypical antipathogenic display films and to demonstrate the effectiveness of the coatings in real hospital environments. Thomas Preußner, technical project manager at Fraunhofer FEP, describes the current status: "Our first tests on the transfer to flexible films already show crystalline structures on the substrates. We are currently working on the stability of the layers produced. To make the transfer to flexible films a success, we are using our existing process expertise and looking at the entire layer production process, starting with layer deposition using large-area magnetron sputtering and crystallization of the layers using inline FLA through to the deposition process of the inorganic acid groups." If the project partners succeed in producing the dual-action, antipathogenic layers on film substrates, they will be able to use roll-to-roll processes to provide highly efficient and economical coating processes that support the transfer to industrial production. The Swedish partner ChromoGenics will contribute its expertise in the production of functional films and is working on roll-to-roll processes within the project. In order to ensure that the subsequent introduction of such products into real environments is successful from the outset, the project partner Fraunhofer ISI will accompany the research work and assess its ecological, economic and social aspects and effects. The Swedish partner Nanoform Science AB is also on hand to market the results at a later date.
New perspectives for interior solutions
The use of such coatings in the construction and building sector, especially for surfaces that regularly come into contact with people, opens up new perspectives for hygienic indoor solutions that significantly improve health safety. If scaling into cost-effective roll-to-roll production processes is successful, other applications are conceivable in addition to use in the building sector, e.g. in vehicle construction or display applications.
Literature
[1] C. Suetens et al, "Prevalence of healthcare-associated infections, estimated incidence and composite antimicrobial resistance index in acute care hospitals and long-term care facilities: results from two European point prevalence surveys, 2016 to 2017", Eurosurveillance, 2018, vol. 23/46.
[2] German Bundestag, https://www.bundestag.de/presse/hib/kurzmeldungen-973282
