Self-sterilizing polymer proves effective against drug-resistant pathogens

Researchers at North Carolina State University have discovered that an elastic polymer has broad-spectrum antimicrobial properties, allowing it to kill a range of viruses and drug-resistant bacteria in just a few minutes, including methicillin-resistant bacteria. Staphylococcus aureus (MRSA).

"We were exploring a different approach to the creation of antimicrobial materials when we observed an interesting behavior of this polymer and decided to explore its potential further," said Rich Spontak, co-authoring author of an article on work and distinguished professor of chemistry. and biomolecular engineering at NC State. "And what we have found is extremely promising as an alternative weapon to existing approaches to materials in the fight against drug-resistant pathogens. This could be particularly useful in clinical environments – such as hospitals or doctor's offices – as well as in seniors' facilities, where the transmission of pathogens can have disastrous consequences. "

The antimicrobial properties of the polymer come from its unique molecular architecture, which attracts water to a sequence of chemically modified (or functionalized) repeating units with sulfonic acid groups.

"When the microbes come in contact with the polymer, the water on the surface of the microbes interacts with the sulfonic acid functional groups of the polymer, creating an acidic solution that quickly kills the bacteria," says Reza Ghiladi, badociate professor of chemistry at NC. State and corresponding author of the article. "These acidic solutions can be made more or less potent by controlling the number of sulfonic acid functional groups in the polymer."

The researchers tested the polymer against six types of bacteria, including three strains resistant to antibiotics: MRSA, vancomycin resistant Enterococcus faeciumand carbapenem resistant Acinetobacter baumannii. When 40% or more of the polymer units concerned contain sulfonic acid groups, the polymer kills 99.9999% of each strain of bacteria in less than five minutes.

The researchers also tested the polymer against three viruses: a similar virus for rabies, an influenza strain and a human adenovirus strain.

"The polymer has been able to completely destroy the flu and the rabies badogue in five minutes," says Frank Scholle, an badociate professor of biological sciences at NC State and co-author of the article. "While the polymer with lower concentrations of sulfonic acid groups had no practical effect on the human adenovirus, it could destroy 99.997% of this virus at higher sulfonic acid levels."

The researchers feared that the antimicrobial effect of the polymer could become progressively worse over time, with the sulfonic acid groups being neutralized when they interacted with positively charged ions (cations) in the water. However, they discovered that the polymer could be fully "recharged" by exposing it to an acidic solution.

"In the lab, you can do that by dipping the polymer into a strong acid," says Ghiladi. "But in other settings, such as in a hospital room, you can simply spray vinegar on the surface of the polymer."

This process of "refilling" works because whenever one of the negatively charged sulfonic acid groups combines with a cation in water – which can occur when the polymer comes into contact with microbes – the sulfonic acid group becomes electrically neutral. This makes the acid group ineffective against microbes. But when the neutralized polymer is subjected to an acid, these functional groups can exchange bound cations with protons from the acid, making the sulfonic acid groups active again – and ready to destroy the agents. microbial pathogens.

"Our work highlights a promising new approach to creating antimicrobial surfaces for use in the fight against drug-resistant pathogens – and nosocomial infections in particular," Ghiladi said.

"Functional block polymers such as this one are very versatile – usable as water treatment media, soft actuators, solar cells and gas separation membranes – and environmentally friendly because they can be easily recycled and recycled. reused, "adds Spontak. "These features make them particularly attractive for widespread use.

"And this work focused on a single series of polymers made by Kraton Polymers," says Spontak. "We are very excited to see how we can further modify this polymer and other polymers to maintain these effective, fast-acting antimicrobial properties, while enhancing other features that would be of interest for other applications."

The document, "Intrinsically self-sterilizing multiblock loaded polymers that kill drug-resistant microbes in minutes", is published in the journal Horizons Materials. The first author of the article is Bharadwaja S. T. Peddinti, Ph.D. student at NC State. The document was co-authored by Mariana Vargas, an undergraduate student at NC State; and Steven Smith of The Procter & Gamble Company.

The work was supported by the Nonwovens Institute at NC State. The researchers also received imaging badistance from the NC State Cellular and Molecular Imaging Center, which is supported by the National Science Foundation under grant number DBI-1624613.

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Note to editors: The summary of the study follows.

"Intrinsically self-sterilizing multiblock polymers that kill drug-resistant microbes in minutes"

authors: Bharadwaja S. Peddinti, Frank Scholle, Mariana G. Vargas, Reza A. Ghiladi, and Richard J. Spontak, North Carolina State University; and Steven D. Smith, from Procter & Gamble

published: July 17th Horizons Materials

DO I: 10.1039 / C9MH00726A

Abstract: Drug-resistant microbes pose a growing threat to healthcare worldwide by dramatically increasing the risk of infections contracted in hospitals that could potentially become life-threatening, particularly for elderly, injured and immunocompromised patients. As a result, several antimicrobial strategies related to materials have been developed to mitigate this ubiquitous concern, resulting in different levels of success and, in some cases, introducing complications that are detrimental to environmental safety. Here, we demonstrate that charged multiblock polymers in which the central block is selectively sulfonated, and therefore hydrophilic and water-swell, inherently provide self-sterilizing surfaces that act rapidly (eliminating more than 99.9999% in just 5 min) positive and negative bacteria, three of which are resistant to antibiotics. This surprising response, which depends on the degree of sulphonation of the average blocks, is attributed to a dramatic reduction in surface pH, a remarkable efficiency against the anionic outer membrane microbes. These polymers, which can be used in biomedical applications, smart textiles, separation membranes, common accessories and food packaging, are also effective against infectious virus strains. Although the antimicrobial efficacy of these polymers is progressively diminished by the complexation of sulfonic acid groups with cationic species during cyclic exposure to electrolytic solutions, these thermoplastic elastomers can be fully rejuvenated at their performance level maximum by relatively short immersion in acidic solutions. As a very promising supplement and alternative design paradigm to the expanding arsenal of antimicrobial materials, these medium block sulphonated multi-block polymers provide an easy, inexpensive, comprehensive and environmentally friendly preventative pathway to combat the global proliferation of drug-resistant microbes.