In the early days of the COVID-19 pandemic, much of the world discovered a lack of personal protective equipment (PPE) — particularly masks — to protect wearers against the virus. Not only did this point to an overall lack of preparation, it has also revealed broken links in the global supply chain.

Masks of all kinds — N95, surgical, cloth — critical equipment, gloves, hand sanitizer and even toilet paper were (and in some regions of the world, still are) in short supply. In the case of masks specifically, makers and manufacturers sought to remedy the problem, devising new and unique solutions for making the masks reusable. The following is an overview of just a handful of those creative attempts.

Heat

Source: MITIn response to the mask shortages due to the COVID-19 pandemic, engineers at Massachusetts Institute of Technology (MIT) created face masks that inactivate the COVID-19 virus with heat, making the masks suitable for reuse.

The MIT mask is made up of antimicrobial copper mesh that is heated to a temperature of 194° F to reduce viral particles from entering the wearer’s mouth or nostrils — which are the entry points for the virus.

Instead of having to heat the wearer’s face, causing him or her discomfort, the mask is heated via an electrical current, which reportedly runs across the 0.1 mm thick copper mesh, powered by a 9 V battery.

According to the MIT engineers, the copper mesh functions as a reverse-flow reactor wherein the wearer breathes in and out so that the airflow constantly reverses, thereby passing the virus back and forth through the mesh and subsequently inactivating it. Then, purified air is filtered through the mask’s side vents.

Cotton candy

The COVID-19-related mask shortage, or, in this case, the mask filter shortage, prompted a physicist from the Physics Unit at Okinawa Institute of Science and Technology (OIST) Graduate University in Okinawa, to devise a technique for manufacturing filters for N95-like respirator masks using a cotton candy machine.

Source: Joseolgon/CC BY-SA 3.0

OIST physicist Mahesh Bandi heated plastic — plastic water bottles and plastic shopping bags, for instance — and then placed the material in a cotton candy machine (otherwise known as a candy floss machine). Once inside, the plastic was spun into a mesh-like material that resembles cotton candy but that is also electrocharged due to the spinning.

The material is then cut into squares and positioned close to a standard air ionizer vent to enhance the material’s electrostatic charge.

In the lab, the filters were placed inside 3D-printed masks designed in the likeness of N95 respirators. According to Bandi, the filters performed as well as standard N95 masks that feature electrocharged filters capable of capturing viruses — including SARS-CoV-2 viruses like COVID-19 — before reaching the wearer.

Sunlight

Another effort to make masks reusable in response to the COVID-19 pandemic and its associated supply chain shortages, researchers from the University of California, Davis, have developed a cotton mask that can disinfect itself when exposed to sunlight.

Source: Adapted from ACS Applied Materials & Interfaces 2020, DOI: 10.1021/acsami.0c15540)

To develop the antimicrobial fabric, which researchers determined kills 99.9999% of bacteria and viruses on the surface of masks within 1 minute of sunlight exposure, the researchers used a relative oxygen species (ROS). When exposed to sunlight, the ROS kills microbes that collect on the mask’s surface and are still contagious despite most cloth masks being capable of filtering out nanoscale aerosol particles.

Researchers applied positively charged chains of 2-diethylaminoethyl chloride (DEAE-Cl) to standard cotton and then dyed that cotton in a negatively charged photosensitizer (a compound that emits ROS when exposed to light) solution. The negatively charged photosensitizer linked to the DEAE chains via electrostatic interactions.

The fabric was created using a dye called rose Bengal, which functioned as the photosensitizer and the fabric reportedly inactivated 99.9999% of the applied T7 bacteriophage (which is a virus believed to be more resistant to ROS than assorted coronaviruses) within half an hour of exposure to sunlight.

Electric cooker

Because disinfection permits reuse of PPE, researchers at the University of Illinois determined that dry heating, and thus sanitizing, masks for reuse could be accomplished via electric cooker.

Dry heating for 50 minutes at 100° C in an electric cooker reportedly decontaminated N95 respirators without affecting the masks’ filtration and fit properties. In the lab, the masks injected with four different viruses, including the coronavirus, were decontaminated using these thermal inactivation mechanisms.

Ozone gas

Researchers from the Georgia Institute of Technology have determined that ozone gas could be used to disinfect PPE.

To demonstrate the effectiveness of ozone gas as a disinfectant, researchers tested it on gowns, masks, face shields, goggles and respirators that were exposed to two viruses with similarities to coronavirus.

In a vacuum chamber with no less than 50% humidity, the researchers demonstrated that the introduction of ozone gas deactivated the viruses on the PPE.

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