Antibacterial surfaces contain antimicrobial agents who destroy bacteria or their ability to reproduce. Same antibacterial properties will help destroy virus. Despite considerable efforts the problem related to infection persits. Today widespread need of antivirus protection and general surfaces disinfection is in all agendas as we have seen media giving wides ranges figures about life time COVID19 can last on different surfaces. London Imperial College researchers published a work showing viral DNA stayed over a bed rail in a hospital room for ten to 18 hours in surfaces, including door handles chairs etc. Paying attention to the level of hygiene is a widespread task in several industries. In this context the antibacterial coatings will provide a long lasting antibacterials protection, and can also improve the cleanliness of any devices or surfaces. Available techniques and materials for surface coatings can get very different efficiency results on antibacterial properties . Thereby, after seeing how some metals can be used as coatings, we will pay attention to the way these coatings are investigated in Medical devices and food industry, to finally see how thin films which are used to achieve enhanced decorative colors for door handles, cutlery or plastics and metals in the faucet industry.
Antibacterial properties vary significantly according to the different metals and the effectiveness of metals to resist bacterial attachment varies depending on the bacterial strain. For a metal such as the copper bacteria are quickly destroyed by his surface.The antimicrobial activity of copper and copper alloys is now well established. Indeed, in 2008 copper was registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material. Touch surfaces commonly found in hospitals such as door handles, touch plates, bed rails, call buttons, or toilet seats can be highly contaminated with microbes. Thereby, there is an intense interest in the use of copper as a self-sanitizing materia, which provides protection from infectious microbes by reducing surface contamination. Dry copper surfaces in laboratory settings and in hospital trials proved to have great killing efficiency against a wide range of microbes, better than most copper surfaces. Similarly, metals such as cobalt, nickel, copper, zinc, zirconium, molybdenum or lead also have antibacterial properties. Expect pure titanium and Titanium Nitride do not exhibit antibacterial properties. Adding silver to TiO2 (which has antibacterial properties) improves the efficiency of the antimicrobial activity. TiO2 is used as a thin film so, in order to deposit the silver particles on the TiO2 films, the chemical photoreduction method can be used. Other methods as PVD (Physical Vapor Deposition) sputtering Ti/Ag alloys are currently being tested. Other possibility is combination of layer evaporation of Silver and TiO2 via electron beam.
For that matter, we saw previously that some metals like copper have natural and efficient antibacterial properties.Those properties can be used in the healthcare industry where a high level of hygiene is required.
In hospitals the use of antibacterial materials helps to reduce nosocomial infections. To prevent the HCAIs (healthcare associated infections) which cause significant morbidity and mortality, the use of materials that contain copper in surfaces in the hospital environment is important. Indeed, antimicrobial surfaces and copper kills a big range of microorganisms, thereby it does reduce the microbial contamination of the environment. These surfaces are installed in toilet seats, tap handles and door push plates because contamination of hand contact surfaces is an important reservoir of microorganisms. Another important infection in medical sector is related to orthopedics and surgery with PTI (pint tract infection). It is the most commonly expected complication when using an external bone fixation when bones are broken. Silver (Ag), titanium zirconium nitride (Ti-ZrN) and Ti-ZrN silver (Ti-ZrN/Ag) coatings have the potential to reduce the viability of bacteria that result in pin tract infections. Also, Zirconium nitride has been recognized as a potential biomaterial due to its excellent resistance to corrosion, good chemical stability and biocompatibility. zirconium nitride-silver displayed the most efficacious antimicrobial properties in relation to its tribological properties. All this thin films coatings are well know in a complete different sector: metallurgy hard coating for cutting tools and tribology applications. There are generally applied over steel alloys by PVD (Physical Vapor Deposition) sputtering or arc deposition.
After proving its effectiveness in the healthcare industry the antibacterials coatings can also be adapted to another industry where hygiene matters : the food industry. Food industry is a sector where antibacterial coatings are widespread. But innovation can have giant role to play. The World Health Organization (2019) estimates that 600 million people fall ill and 420,000 die each year due to contaminated food. In this context the sector developed new ways to upgrade their equipment and packaging. Microbial cross-contamination represents a significant challenge to maintaining product shelf life and food safety, quality, and security. Antimicrobial materials are a potential means to reduce such microbial cross-contamination by inactivating microorganisms that adhere to them. Metal coated surfaces have a potential antimicrobial activity. Among them Copper has the most efficient potential followed by silver and zinc surfaces. Evaporation thin films process are well know in roll to aluminization of plastics bags.
These protective coating methods using thin films can be extended in our daily life. For example decorative colors coating of door handles or cutlery in hospital can replace or improve brass or stainless steel materials.
Titanium and zirconium are already widely used in decorative thin films of metals parts but also adding copper coatings can be a good progress.Decorative coating with PVD thin films can produce colors and textures that can not be achieved with spray or dip coating. The coloured surface coatings that can be obtained using PVD include: gold (TiN), rose gold (ZrN), bronze (TiAlN), blue (TiAlN), black (TiAlCN), as well as a dark red (ZrN). PVD and electroplating are two methods used for thin films coatings. The PVD process provides a more uniform deposit, improved adhesion up to six times greater in some cases, wider choice of materials to be deposited and there are no harmful chemicals to dispose of, so it is more environmentally friendly. PVD colours will not fade over time and have the benefit of being more uniform in appearance and more abrasion-resistant than colouring which is done by the electrochemical processes. Furthermore, PVD can produce alloys that cannot be produced by any other method.
To conclude, we saw that the antibacterial properties of coatings are needed in several industries: food (packaging, equipment) or in the healthcare industry (medical supplies or decorative coatings) or even at home. The antibacterial coatings are part of our daily life and can make it easier and safer. The demand for antimicrobial coatings keeps growing, manufacturers are looking to embed the surfaces of their devices with a long-lasting and cost effective coatings agent. COVID19 has exposed the need of further and deeper studies of antibacterial coatings. Along with technical advancements in antimicrobial coatings, Photon Export provides the materials or alloys for PVD surface coaters that want to enhance antibacterial properties on their coated surfaces. Photon Export can also provide PVD coating services to implement new coating possibilities and help validating antibacterial efficiency on surfaces.
Authors: Meritxell Garcia / Gilliane Opinimo
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