International. Developed by a team of engineers and immunologists at the University of Michigan, it proved deadly for SARS-CoV-2 (the virus that causes COVID-19) and a variety of other pathogens.
The coating killed 99.9% of the microbes even after months of cleaning, abrasion and other repeated punishments on real-world surfaces such as keyboards, cell phone screens and cutting boards smeared with chicken.
According to Anish Tuteja, a professor of materials science and engineering at the University of Michigan, the coating could be a game-changer in public spaces traditionally laden with germs, such as airports and hospitals.
"We've never had a good way to keep constantly touching surfaces, like airport touchscreens, clean. Disinfectant cleaners can kill germs in just a minute or two, but they dissipate quickly and leave surfaces vulnerable to reinfection," said Professor Tuteja.
Tutela noted that "we have long-lasting antibacterial surfaces based on metals such as copper and zinc, but they take hours to kill bacteria. This coating offers the best of both worlds."
The coating, which is transparent and can be brushed or sprayed, gets its durability and germ-killing power by combining tried and true ingredients in a new way. It uses antimicrobial molecules derived from tea tree oil and cinnamon oil.
The durability of the coating comes from polyurethane, a sturdy varnish-like sealant that is commonly used on surfaces such as floors and furniture.
"The antimicrobials we tested are classified as 'generally considered safe' by the FDA, and some have even been approved as food additives. Polyurethane is a safe and very commonly used coating. But we did toxicity testing just to be sure, and we found that our combination of ingredients is even safer than many of today's antimicrobials," Tuteja said.
The results of the study's durability tests suggest that the coating could continue to kill germs for six months or more before its oil begins to evaporate and reduces its disinfectant power. But even then, according to Professor Tuteja, it can be recharged by cleaning it with new oil; the new oil is reabsorbed from the surface, restarting the cycle.
Tuteja estimates that the technology could be commercially available within a year; has been licensed to Hygratek. The key challenge was to combine the oil and polyurethane in a way that would allow the oil molecules to do their job of removing germs and prevent them from evaporating quickly.
The research team found a possible solution in cross-linking, a well-known process that uses heat to bind materials together at the molecular level. The smaller oil molecules easily combined with the cross-linked polymer molecules, forming a stable matrix.
But to kill germs, oil molecules need to penetrate their cell walls, which they can't do if they're tightly tied to the matrix. Eventually, they found a middle ground by partially crisscrossing the materials, enough to keep some of the oil molecules free to do their job, but keeping others firmly attached to the polyurethane.
"There was some trial and error, but we finally found that cross-linking only part of the oil did what we needed. The free oil tends to stick with the oil that's crisscrossed in the matrix, which helps the coating last longer," Tuteja said.
Tuteja emphasizes that they are not enclosed in a specific formula; The team's understanding of the properties of individual ingredients allows them to modify the formula for specific applications or rebalance antimicrobial agents to kill specific germs.
"Our goal is never just to develop a unique coating, but to develop a library of underlying material properties to take advantage of. If we can understand those properties, then we can develop coatings to meet the needs of specific applications," said the professor and researcher.
