As highlighted during the COVID-19 pandemic, face masks lower the risk of viral infection by reducing the spread of respiratory droplets.
FDA spokesperson Audra Harrison told Medical News Today that, to date, National Institute for Occupational Safety and Health (NIOSH)-approved N95 respirator masks are “the gold standard for respiratory protection for healthcare personnel.”
However, traditional masks — including N95s — are not able to deactivate viruses on contact.
The risk of contamination increases with wear time, and healthcare workers are advised to dispose of face masks after patient exposure. This may lead to mask shortages and generate significant plastic waste.
But researchers at Rensselaer Polytechnic Institute (RPI) in New York developed a method that gives antiviral and antibacterial properties to N95 face mask filters. They found that incorporating materials with antiviral properties into face masks improved their ability to protect against infection while also prolonging wear time and thus reducing plastic waste.
The new research was published in the June issue of ACS Applied Materials & Interfaces.
How the N95 face mask was modified
Prior research has created face masks with antiviral activity by incorporating metal nanomaterials capable of deactivating viruses, such as copper, in the filter fibers.
However, researchers were concerned that metal nanomaterials could detach from the mask filter and be inhaled, causing toxicity.
Polycations — long-chain molecules with a net positive charge — can be used instead of metal nanomaterials to endow surfaces with antiviral activity. Previous studies documented the ability of polycations to kill bacteria and viruses upon contact by disrupting their cell membranes.
Dr. Helen Zha, assistant professor of chemical and biological engineering at Rensselaer and co-author of the new face mask research, explained the polycation-based method she and her research team developed in a press release. The method confers antimicrobial properties to polypropylene fabric, which is commonly used as a filtration material in N95 masks.
“The process that we developed uses a really simple chemistry to create this non-leaching polymer coating [on top of the N95 mask filter material] that can kill viruses and bacteria by essentially breaking open their outer layer.”
– Dr. Helen Zha
Dr. Zha’s team applied a quaternary ammonium polymer (a polycation) to polypropylene fiber surfaces, using ultraviolet (UV) light to drive the grafting process. The resulting ultra-thin polymer coating gives the filter a permanent positive charge without greatly changing the fiber structure or the breathability of the filter.
Antibacterial and antiviral activity
The researchers found that the polymer-coated polypropylene could deactivate several lipid-enveloped viruses, as well as Staphylococcus aureus and Escherichia coli bacteria, upon contact.
The antiviral activity of polymer-coated polypropylene was tested using different viruses. These included a mouse coronavirus similar to the human coronavirus SARS-CoV-2, a human coronavirus, and a suid herpesvirus (also called pseudorabies virus). After contact with the coated filter, the number of infectious viral units decreased, although antiviral activity varied significantly depending on the virus strain and the method for quantifying infectious virus.
Based on antimicrobial mechanisms described in previous studies, the researchers believe that positively-charged polypropylene kills viruses and bacteria upon contact by disrupting their cell membrane.
The researchers noted that the filtration efficiency of the N95 filter decreases after the application of the antimicrobial polymer coating.
However, this issue can be resolved by wearing an unaltered N95 mask under the polymer-coated mask.
In the future, mask manufacturers could use antimicrobial polymer in the exterior layer of the N95 mask.
Commercialization and other applications
The antimicrobial polymer-coating process can be applied to existing mask filters, rather than requiring the manufacture of new ones.
However, the polymer coating method was also designed “to facilitate commercialization” Dr. Zha told MNT.
“We purposely used reagents, solvents, and equipment that are readily available. We pursued simple chemistries and methods that have the potential to be scaled up,” said Dr. Zha. “I think that there’s a viable pathway for scaled-up manufacturing and commercial realization.”
According to a press release, Shekhar Garde, dean of the School of Engineering at Rensselaer, referred to the antimicrobial polymer coating method as “a smart strategy” and pointed out its versatility.
“Given the abundance of polypropylene in daily life, perhaps this strategy is useful in many other contexts, as well,” Garde said.