Zinc-embedded polyamides inactivate SARS-CoV-2 and influenza A

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A viruses (IAVs) can spread via liquid droplets and aerosols. These viruses can be prevented from spreading by wearing face masks or other personal protective equipment (PPE). However, IAV and SARS-CoV-2 are stable for hours on various materials. Thus, the frequent and correct disposal of these PPE becomes crucial and also requires decontamination processes for reuse.

Many studies report the use of silver nanoparticles, copper nanoparticles, cuprous oxide (Cu₂O) or cupric oxide (CuO) spays, and copper or zinc surfaces or fibers to inactivate the virus; however, many confounding factors such as adsorption of viruses make it difficult to measure and optimize the inactivation characteristics.

In a recent study, interdisciplinary researchers demonstrated how they removed the IAV H1N1 and the SARS-CoV-2 from woven PA66 fabric to measure the number of remaining active viruses. Using this advancement, they found that a zinc-containing polyamide 6.6 (PA66)-based fabric decreased the IAV H1N1 and pandemic SARS-CoV-2 titer by approximately 2-logs (100-fold).

“This reduction is more than sufficient to inactivate the number of infectious IAV particles (∼24 plaque-forming units [pfu]) present in a cough,” observed the researchers.

The study provides new insights into the development of testing protocols for “pathogen-free” fabrics. This research is published in the journal ACS Applied Materials & Interfaces.

The researchers show that the fabric retains its virus-inactivating property and stable zinc content over 50 standardized washes.

The viral particles

The IAV particle consists of a double-layered membrane in which multiple copies of the viral hemagglutinin (HA), matrix 2 (M2), and neuraminidase (NA) proteins are embedded. The SARS-CoV-2 virion consists of a double-layered membrane, and the membrane proteins spike (S), envelope (E), and matrix (M).

Infection of a host cell requires binding of the SARS-CoV-2 S protein to the cellular receptor ACE2, while IAV uses its HA protein to bind sialic acid receptors.

Need for a robust antiviral strategy for PPE

The most effective way to stop the spread of new viruses is to inhibit or inactivate these viruses before they become epidemics or pandemics. PPE, such as coats, face masks, gloves, etc., should also be decontaminatable readily and repeatedly.

Because respiratory viruses are stable for days to hours on fabrics, there is a need for newly developed PPE that can trap and inactivate respiratory viruses.

“So far, few studies have investigated if metal ions embedded in fabrics can inactivate RNA viruses, in part because absorbance and fabric density differences present confounding factors that inactivation protocols do not account for,” noted the researchers in their paper.

The study

To better understand how respiratory RNA viruses are adsorbed and inactivated, the researchers added IAV and SARS-CoV-2 to the International Antimicrobial Council (IAC) issued cotton, a textile PA66 fabric, and polypropylene (PPP). The researchers found strong liquid absorption by cotton and PA66 in PBS (phosphate buffer solution) and that the addition of mild tween-80 resulted in efficient virus release from PA66 but not from cotton.

Therefore, the risk of reinfection from virus released from cotton masks after the wash is minimal as cotton does not release IAV or SARS-CoV-2 efficiently.

“By contrast, virus retention on PPP, which is used for the construction of disposable 3-ply masks, is poor, in line with its hydrophobic properties,” added the researchers.

Although copper and zinc surfaces or particles can inactivate IAV strains, SARS-CoV-2, and seasonal CoV HCoV-229E, and PPP imbued with copper oxide can inactivate IAV, the researchers used zinc in this study mainly because of three reasons: 1) zinc has a much higher propensity to ionize than copper, thereby providing a much faster reaction potential; 2) zinc oxide is considered a Generally regarded as Safe (GRAS) compound by the FDA, which can speed up the development process; 3) zinc does not cause discoloration of the polymer or fabric, enabling broader applicability.

The tests on zinc showed that zinc ions could inactivate an IAV H1N1 strain by destabilization of the viral surface proteins.

After constructing the fabric using zinc oxide, the researchers tested for zinc leaching under rigorous washing cycles – to find that the zinc ions were highly stable on the fabric. They analyzed the virus titers in the washed fabrics and observed that the fabric reduced the IAV titer by approximately 2-logs – property retained up to 50 washes. “Overall, these results suggest that the PA66 fabric containing zinc can inactivate both IAV and SARS-CoV-2 and that this property is retained after 50 washes,” the researchers said in the paper.

Conclusion

This fabric containing the zinc ions successfully inactivated the IAV and the SARS-CoV-2 titer by approximately 2-logs. PPE made out of such potent reusable pathogen-free materials could be a good shield. Our findings may be important for healthcare workers who are exposed to infected patients for prolonged periods, people with underlying risk factors needing additional protection, and people who need to frequently remove their PPE, the researchers write.

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.