In our centuries-old struggle against germs, we may soon have a new weapon: the first long-lasting coating that can kill bacteria and viruses in minutes and continue to kill them for months at a time.
Developed by a team of University of Michigan engineers and immunologists, it proved deadly to SARS-CoV-2 (the virus that causes COVID-19), E. coli, MRSA and a variety of other pathogens. It killed 99.9% of microbes even after months of repeated cleaning, abrasion and other punishment on real-world surfaces like keyboards, cell phone screens and chicken-slathered cutting boards.
According to Anish Tuteja, a professor of material science and engineering at U-M and co-corresponding author of the research published in Matter, the coating might be a game changer in typically germ-infested public venues such as airports and hospitals.
“We’ve never had a decent way to keep constantly-touched surfaces clean, like airport touch displays,” he explained. “Disinfectant cleansers may kill germs in a matter of seconds, but they swiftly fade, leaving surfaces exposed to reinfection. We do have antibacterial surfaces that are long-lasting and made of metals like copper and zinc, but they take hours to destroy germs. This coating combines the benefits of both worlds.”
The transparent coating, which may be brushed or sprayed on, receives its resilience and germ-killing power from a novel combination of tried-and-true chemicals. It employs antimicrobial compounds derived from tea tree oil and cinnamon oil, both of which have long been utilised as safe and powerful germ killers that operate in less than two minutes. Polyurethane, a strong, varnish-like sealant often used on surfaces such as floors and furniture, provides the coating’s longevity.
“The FDA classifies the antimicrobials we tested as ‘generally considered as safe,’ and several have even been approved as food additives,” Tuteja explained.
“Polyurethane is a safe and widely used coating. But, just to be sure, we conducted toxicity testing and discovered that our specific mix of chemicals is even safer than many of today’s antimicrobials.”
According to the findings of the study’s durability tests, the coating might destroy germs for six months or more until its oil evaporates, reducing its disinfection efficacy. Tuteja claims that it may still be recharged by wiping it with fresh oil; the new oil is reabsorbed by the surface, restarting the cycle.
Tuteja believes the technology will be commercially accessible within a year; it has been licenced to Hygratek, a spinoff firm created by Tuteja with help from U-M Innovation Partnerships.
The main issue was to blend the oil and polyurethane in such a manner that the oil molecules could accomplish their germ-killing activity while not evaporating fast. The research team, which included Geeta Mehta, associate professor of materials science and engineering and biomedical engineering, and PhD students Abhishek Dhyani and Taylor Repetto, co-first authors, discovered a possible solution in cross-linking, a well-known process that uses heating to link materials together at the molecular level. The smaller oil molecules quickly joined with the cross-linking polymer molecules, resulting in the formation of a stable matrix.
However, in order to kill germs, oil molecules must enter their cell walls, which they cannot accomplish if they are strongly linked to the matrix. They eventually discovered a happy medium by partially cross-linking the materials – just enough to keep some of the oil molecules free to conduct their function while keeping others snugly linked to the polyurethane.
“There was some trial and error,” Tuteja explained, “but we soon discovered that cross-linking only portion of the oil achieved what we required.” “The free oil prefers to stick with the oil that’s cross-linked into the matrix, extending the life of the coating.”
Once the fundamental recipe was established, the researchers went about identifying a mixture of active substances capable of killing a wide range of the bacteria that cause the greatest problems for people. They collaborated with co-corresponding authors Christiane E. Wobus, an associate professor of microbiology and immunology, and J. Scott VanEpps, an assistant professor of emergency medicine, both at the University of Michigan Medical School, to select a representative sample of bacteria. Finally, scientists discovered an exact mix of antibacterial compounds that were efficient, safe, and cheap.
Tuteja notes that they are not bound by a single formula; the team’s mastery of the qualities of various chemicals allows them to alter the recipe for certain uses or rebalance the antimicrobial agents to kill specific microorganisms.
“Our objective is never to create a one-off covering, but rather to create a library of underlying material qualities from which to draw,” Tuteja explained. “We can build coatings that satisfy the demands of certain applications if we understand their qualities.”