A simple kitchen sink experiment helped Northwestern researchers discover that green tea leaves not only can be used to steep a good cup of tea, but they make an excellent antibacterial coating, too.
And so can red wine, dark chocolate and cacao beans, they found. It’s the powerful and healthful polyphenols at work in a new way. (Polyphenols are naturally occurring molecules found in plants whose functions include structural support and defense against bacteria and oxidative damage.)
Polyphenols are sticky, and the researchers exploited this useful property, while also retaining some of the compounds’ well-known biological properties. They made new multifunctional coatings based on tannic acid and pyrogallol—inexpensive compounds resembling the more complex polyphenols found in tea, wine and chocolate.
Simply dissolving polyphenol powder in water with the proper dash of salt quickly produces colorless coatings that have antioxidant properties, are non-toxic and can kill bacteria on contact.
The coatings—which can stick to virtually anything, including Teflon—could be used on a wide range of consumer, industrial and medical products, from catheters and orthopedic implants to membranes for water purification and materials used in food processing, packaging and preparation.
The study was published on August 22 in the journal Angewandte Chemie.
“We discovered a way to apply coatings onto a variety of surfaces that takes advantage of the sticky properties of the polyphenol compounds,” says Phillip B. Messersmith, biomedical engineering, who led the research. “It’s a very simple dip-coating process, and the antibacterial and antioxidant properties are preserved in the coating.”
One could take a stainless-steel hip implant, he says, apply the process to it, and the coating that emerges spontaneously and with no other modifications will kill bacteria and quench reactive oxygen species, such as free radicals.
Messersmith’s team tested all kinds of materials—medically relevant polymers, engineering polymers, metals, inorganic substrates and ceramics—and a coating stuck to each one. The researchers also demonstrated they can easily modify the coatings to give them additional functions, such as an antifouling property to prevent cells from building up on a surface, such as a pacemaker.
“What’s interesting is that the raw materials we regularly encounter in our diets can benefit us in a way we had never envisioned—as coatings on medical devices,” says Tadas S. Sileika, a graduate student in Messersmith’s lab and first author of the paper.
Article by Megan Fellman