Researchers at Northwestern University, Evanston, IL, discovered that natural products, like green tea leaves, red wine, dark chocolate, and cacao beans could inspire excellent antibacterial coatings. That’s because they all contain polyphenols, naturally occurring plant molecules that defend against bacteria and oxidative damage.

Natural products rich in polyphenols inspired a new form of antibacterial coating.

Since polyphenol compounds are sticky, the researchers used tannic acid and pyrogallol—inexpensive compounds resembling the more complex polyphenols in tea, wine, and chocolate to make new multifunctional coating materials that have antioxidant properties, are non-toxic, and can kill bacteria on contact.

The team of scientists say that the coatings can stick to virtually anything, including Teflon, and 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.

"It's a very simple dip-coating process, and the antibacterial and antioxidant properties are preserved in the coating," said Phillip B. Messersmith, Erastus O. Haven Professor of Biomedical Engineering at Northwestern's McCormick School of Engineering and Applied Science, who led the research. One could take a stainless-steel hip implant, he said, apply the process, and the coating that emerges will kill bacteria and quench reactive oxygen species, such as free radicals.

Messersmith's team tested all kinds of materials, including medically relevant polymers, engineering polymers, metals, inorganic substrates, and ceramics, and demonstrated that a coating stuck to each one. They were also able to 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.

The coatings have innate properties that, without further modification, can help prolong the life of a medical device, reduce inflammation in a patient, and prevent bacterial infections, they said. In addition, the coatings are only 20 to 100 nanometers thick, depending on the material being coated, so would not alter biomedical instruments in a negative way.