Aug 5 2019
A research team from North Carolina State University (NC State) has discovered that an elastic polymer contains broad-spectrum antimicrobial characteristics that allow it to quickly destroy a host of viruses and drug-resistant bacteria such as methicillin-resistant Staphylococcus aureus, or MRSA for short.
We were exploring a different approach for creating antimicrobial materials when we observed some interesting behavior from this polymer and decided to explore its potential in greater depth. And what we found is extremely promising as an alternate weapon to existing materials-related approaches in the fight against drug-resistant pathogens.
Rich Spontak, Study Co-Corresponding Author and Distinguished Professor of Chemical and Biomolecular Engineering, NC State
Spontak continued, “this could be particularly useful in clinical settings—such as hospitals or doctor's offices—as well as senior-living facilities, where pathogen transmission can have dire consequences.”
The antimicrobial properties of the polymer arise from its special molecular design, which lures water to a series of repeat units that are chemically functionalized or altered with sulfonic acid groups.
“When microbes come into contact with the polymer, water on the surface of the microbes interacts with the sulfonic acid functional groups in the polymer—creating an acidic solution that quickly kills the bacteria,” stated Reza Ghiladi, an associate professor of chemistry at NC State and the study’s co-corresponding author. “These acidic solutions can be made more or less powerful by controlling the number of sulfonic acid functional groups in the polymer.”
The team tested the elastic polymer against six forms of bacteria, including three antibiotic-resistant strains—carbapenem-resistant Acinetobacter baumannii, vancomycin-resistant Enterococcus faecium, and MRSA.
The researchers observed that the polymer successfully destroyed 99.9999% of each bacterial strain in less than five minutes, if sulfonic acid groups are present in 40% or more of the pertinent polymer units. In addition, they tested the polymer against three types of viruses such as a strain of human adenovirus, a strain of influenza, and an analog virus for rabies.
The polymer was able to fully destroy the influenza and the rabies analog within five minutes. While the polymer with lower concentrations of the sulfonic acid groups had no practical effect against human adenovirus, it could destroy 99.997% of that virus at higher sulfonic acid levels.
Frank Scholle, Study Co-Author and Associate Professor of Biological Sciences, NC State
One of the major concerns of the scientists was that the antimicrobial effect of the polymer could increasingly worsen over time, because sulfonic acid groups get neutralized upon interacting with positively charged ions, or cations, in water. Conversely, the researchers discovered that the elastic polymer could be fully “recharged” by subjecting it to an acid solution.
“In laboratory settings, you could do this by dipping the polymer into a strong acid,” Ghiladi says. “But in other settings—such as a hospital room—you could simply spray the polymer surface with vinegar.”
This “recharging” process seems to work, because the sulfonic acid group becomes electrically neutral whenever a negatively charged sulfonic acid group integrates with a cation in water—which can occur when the polymer makes contact with the microorganisms.
As a result, the acid group becomes ineffective against the microbial pathogens. However, exposing the neutralized polymer to an acid solution causes those functional groups to exchange the bound cations with the protons from the acid. This reactivates the sulfonic acid groups and makes them ready to destroy the microbes.
“The work we've done here highlights a promising new approach to creating antimicrobial surfaces for use in the fight against drug-resistant pathogens - and hospital-acquired infections in particular,” stated Ghiladi.
Functional block polymers like this are highly versatile—usable as water-treatment media, soft actuators, solar cells and gas-separation membranes—and environmentally benign since they can be readily recycled and re-used,” Spontak added. “These features make them particularly attractive for widespread use.
Rich Spontak, Study Co-Corresponding Author and Distinguished Professor of Chemical and Biomolecular Engineering, NC State
Spontak continued: “And this work focused on only one polymer series manufactured by Kraton Polymers. We are very eager to see how we can further modify this and other polymers to retain such effective and fast-acting antimicrobial properties while improving other attributes that would be attractive for other applications.”
The paper, titled “Inherently self-sterilizing charged multiblock polymers that kill drug-resistant microbes in minutes,” was published in the journal, Materials Horizons. Bharadwaja S. T. Peddinti, a PhD student at NC State, is the first author of the paper. Mariana Vargas, an undergraduate at NC State; and Steven Smith of The Procter & Gamble Company, was co-authored the paper.
The Nonwovens Institute at NC State supported the study. The scientists also received imaging assistance from the NC State Cellular and Molecular Imaging Facility, which is supported by the National Science Foundation under grant number DBI-1624613.