Scientists at MIT have designed a novel face mask that can not only filter out the SARS-CoV-2 virus, which causes COVID-19, but also inactivate it using heat.
The new mask incorporates a heated copper mesh and does not need to be decontaminated or thrown away after use, according to the researchers.
As the person wearing the mask breathes in and out, air flows repeatedly across the mesh, and any viral particles in the air are slowed and inactivated by the mesh and high temperatures, the researchers said.
Such a mask could be useful for healthcare professionals, as well as members of the public in situations where social distancing would be difficult to achieve, such as a crowded bus, they said.
"This is a completely new mask concept in that it doesn't primarily block the virus. It actually lets the virus go through the mask, but slows and inactivates it," said Michael Strano, a professor at Massachusetts Institute of Technology (MIT) in the US.
The researchers have begun building prototypes and hope to begin testing them soon.
The new design has been described in a paper posted on online preprint server ArXiv, and submitted to a peer-reviewed journal.
"The masks that we wear now are designed to capture some of the virus. They do offer protection, but there's no one really thinking about inactivating the virus and sterilising the air. That surprised me," Strano said.
The researchers set out to design a mask that would kill viruses using heat.
They decided to use copper mesh as the heating and capture element, and performed some mathematical modelling to determine the optimal temperature range needed to kill coronaviruses flowing inwards or outwards from natural breathing.
"The vast majority of masks today function by filtration, filtering particles by size or electric charge," said MIT graduate student Samuel Faucher, the lead author of the study.
"This mask relies on a different mechanism and works predominantly by thermal inactivation," Faucher said.
The researchers calculated how rapidly coronaviruses degrade at different temperatures and trapping conditions, and found that a temperature of about 90 degrees Celsius could achieve between a thousandfold and millionfold reduction in viral particles, depending on the final mask size.
They also showed that that temperature can be achieved by running an electrical current across a 0.1-millimetre thick copper mesh or thermoelectric heater, powered by a small battery.
The current prototypes include a 9-volt battery, which would provide enough power to heat the mask for a few hours and would cool the air before it is inhaled.
"Of course, we need to be mindful of the safety and comfort of mask users. The air will be cooled after viral inactivation to make the mask comfortable and safe to use," Faucher said.
The researchers were able to enhance the efficiency of virus deactivation by taking advantage of the breath to create a type of reactor known as a reverse-flow reactor.
As the person wearing the mask breathes in and out, the air flow continually reverses, allowing any viruses in the mask to pass over the mesh many times and making it more likely that they will be deactivated.
Purified air flows out of vents on both sides of the mask, the researchers said.
"This design means you can wear a small mask, something that will fit on your face, but the virus can spend much more time getting deactivated than it would without the reverse flow reactor design," Strano said.
The copper mesh is surrounded by neoprene, an insulating material that prevents the outside of the mask from becoming too hot to wear.
N95 respirators, surgical masks, and cloth masks are effective and should be used during the pandemic as directed, Strano said, but one potential advantage of heated masks is that because they kill the virus, they don't need to be decontaminated or thrown away after use.
They may offer extra protection by eliminating the virus rather than only filtering it.
"What we show is that it's possible to wear something on your face that's not too cumbersome, that can actually allow you to breathe medically sterile air," Strano said.
Heated masks would be more expensive than cloth masks or surgical masks, but they may be useful in situations where exposure risk is high, and cost is less of a concern, the researchers said.