Although existing coatings kill harmful germs on frequently handled surfaces, most of those compounds either need to be applied repeatedly or take a while to affect. However, a new coating created at the University of Michigan may solve both issues using antimicrobial molecules derived from natural oils.
What is the Coating Made of?
The substance is made of polyurethane plastic, tea tree oil, and cinnamon oil. The safety of each component for humans is already well-known. They have been used for centuries as safe and effective germ killers. A new solution uses heat to link the materials together at a molecular level.
The team performed toxicity testing to be sure that the combination of ingredients is even safer than currently available antimicrobials. “The antimicrobials we tested are classified as ‘generally regarded as safe’ by the FDA, and some have even been approved as food additives,” Professor Anish Tuteja said. “Polyurethane is a safe and very commonly used coating.”
How Does the Coating Kill Harmful Bacteria?
The solution is brushed or sprayed onto objects like touchscreens or door knobs while it is still liquid. After drying, it creates a clear, durable coating that effectively eliminates bacteria and viruses.
Some tea tree and cinnamon molecules are free to travel between the plastic matrix and the coating’s surface since they are cross-linked to the polyurethane molecules. Others are confined to the plastic matrix and kept permanently. Yet, the free molecules usually stick with the cross-linked ones, slowing the rate of evaporation of the oils. Consequently, when microorganisms come into contact with the coating, the oil molecules penetrate their cell walls and kill them within two minutes.
Successful Test Results
To evaluate the coating’s effectiveness, the researchers tested the antimicrobial coating on real-world surfaces like keyboards, cell phone screens, and cutting boards with raw chicken. The durability tests showed that the solution held up for at least six months and killed 99.9% of bacteria like MRSA, E. coli, and the SARS-CoV-2 virus that causes Covid-19. Even after being constantly scrubbed and disinfected, it achieved these impressive results.
Eventually, when the oils evaporate, the disinfectant power declines. Then the antibacterial coating can be quickly “recharged” by cleaning it with fresh tea tree and cinnamon oils absorbed by the polyurethane matrix.
Professor Anish Tuteja, professor of material science and engineering at U-M and the co-corresponding author of a paper on the research, explained:
“We’ve never had a good way to keep constantly-touched surfaces like airport touch screens clean. Disinfectant cleaners can kill germs in only a minute, but they dissipate quickly and leave surfaces vulnerable to reinfection. We also have long-lasting antibacterial surfaces based on metals like copper and zinc, but they take hours to kill harmful bacteria. This coating offers the best of both worlds.”
The solution, a potential game-changer, is currently being commercialized by the spinoff company Hygratek. The research was published in Matter on August 23, 2022.
Other Recent Antimicrobial Innovations
The First-of-its-Kind Spray-on Coating
Researchers at the University of Sydney created a different yet highly-effective coating, preventing around 99.9% of bacteria and halting their growth. The spray works in two ways. Professor Antonio Tricoli, the co-lead author of the research, explains the process:
“Like a lotus leaf, the surface spray creates a coating that repels water. Because the pathogens like to be in water, they remain trapped in the droplets and the surface is protected from contamination.If this mechanism fails, a secondary burst of ions is triggered by carefully designed nanomaterials dispersed in the coating.”
The spray coating is safer than existing disinfectants, with no harmful side effects, and has more stable potency.
The authors say the coating can prevent the spread of viruses and bacteria by applying it to various surfaces. These include elevator buttons, stair rails, hospital surfaces, schools, restaurants, and nursing homes.
“For this study, we tested metal surfaces. However, in the past, we have shown the spray can be applied to any surface, for example, blotting paper, plastic, bricks, tiles, glass and metal.” said Professor David Nisbet.
The researchers have created a start-up company to progress the technology and make the spray commercial available within three years.
The research was published in Advanced Science in July 2022.
Copper Nano-coating Research
Copper can eliminate up to 99.9% of harmful bacteria within two hours of contact. This isn’t quite as fast as the newer coating innovations. This is why the University of British Columbia (UBC) has experimented with copper coatings and installed over 400 antimicrobial copper patches on door handles and railings in its buildings.
The new copper coating was created with an innovative process involving copper and zinc called “electrodeposition,” which could offer a low-cost solution for healthcare facilities. The new process has led to an advanced copper coating that can kill certain bacteria quicker than regular unmodified copper.
The new material took just one hour to kill 99.7% of Staphylococcus aureus, a Gram-positive pathogen, compared to two hours for pure copper. “Not only does this coating kill pathogens faster than pure copper, it helps ensure antibiotics remain effective,” said Dr. Amanda Clifford, Assistant Professor in the Department of Materials Engineering. “By using this new formulation, we’re killing pathogens before patients become infected and need to use antibiotics against them, slowing the rise of antibiotic resistance.”
The installation is a part of Teck’s Copper & Health program. The program has also installed copper surfaces on buses, SkyTrain Metro Vancouver cars, and various types of vehicles in Greater Toronto.
“It’s important that we work with industry leaders like Teck, who display a commitment to innovation and sustainability,” said Professor James Olson, Dean, UBC Faculty of Applied Science. “When we work together, we’re able to quicken our research and see its impact in the real world.”
The research was published in Advanced Materials Interfaces in July 2022.
Copper Nanowire Spray
Ames National Laboratory has produced two forms of copper nanowire spray. The first is a pure copper nanowire, just 60 nanometers wide. While the second is a combined copper-zinc nanowire.
Combined with a water or ethanol solution, these create an antimicrobial spray. When sprayed onto glass, plastic, or steel surfaces, the solution creates an antiviral coating.
The pure copper coating inactivated the SARS-CoV-2 virus twice as fast as the copper-zinc coating. However, the copper-zinc coating stays effective for longer, requiring less frequent reapplications.
The research was published in RSC Advances in February.