How to make a homemade mask as good as an N95 – News @ Northeastern


You’ve probably heard that homemade face masks can prevent you from inadvertently spreading the coronavirus when you cough, sneeze, talk, sing, laugh, or breathe out. You may also have heard that they may not be as good at blocking virus particles as N95 respirators, the type of masks designed and tested to prevent medical personnel from inhaling harmful microbes such as the SARS-CoV-2 coronavirus that causes COVID-19.

Steve Lustig is Associate Professor and Associate Research Chair in Chemical Engineering at the College of Engineering at Northeastern. Photo by Matthew Modoono / Northeastern University

But when Steve lustig goes out for a walk, he covers his face with a homemade mask that has the same ability to stop viral particles as an N95. His mask consists of a pair of layers of terry cloth. And Lustig, an associate professor of chemical engineering at Northeastern, trusts him because he and his team have tested these materials in the lab.

After testing how nanoparticles penetrated more than 70 combinations of fabrics, the team find several common material combinations that can be as effective at blocking coronavirus particles as N95s, or even better. The trick, Lustig says, is that the fabrics have to be layered tactically.

“Most fabrics are not as good as official and certified N95 respirators.” Lustig said. “But no one really thought about how many layers it would take for cotton, for example, to be as good as an N95.”

One of the most important aspects of laying a fabric capable of blocking viral particles is combining materials with enough fibers to increase their chances of trapping or absorbing germs.

Another key part of this puzzle is to use at least one diaper with hydrophobic properties, which would repel aqueous substances such as respiratory droplets from a person’s airways and prevent them from passing through the mask. If the fluid wets the tissue, it can move viral material through it.

This combination of layers, along with a tight fit around the face and proper physical distance, can be an important defense system, Lustig says.

A SARS-CoV-2 particle is no larger than a white blood cell or a light dust particle, which human eyes cannot see without a microscope. The coronavirus gets its name from a set of crown-shaped spikes that surround its tightly packed genetic material.

John Biswakarma sprays fluorescent nanoparticles through tissue and measures their concentration as they land on glass slides inside the Interdisciplinary Science and Engineering Complex on April 22, 2020. Photos by Matthew Modoono / Northeastern University

To study how such a tiny and peculiar particle passes through a material, Lustig worked with Ming Su, professor of chemical engineering at Northeastern. Su’s team had developed fluorescent nanoparticles.

Because these nanoparticles were so similar in size to the coronavirus and because they interact the same way SARS-CoV-2 interacts with water, Su prepared a batch specifically for experiments at Lustig’s lab. The idea was also to take advantage of the fluorescence of the nanoparticles to count them after their passage through the tissue using a special microscope.

Lustig’s team dispersed the nanoparticles in water and then sprayed the substance into the air to mimic the coughing and sneezing of a person with the virus. The tests also created different changes in airflow to account for the type of dynamics a wearer creates while breathing, which helps virus particles pass through a material.

“You also breathe through the mask, so we had to replicate that in a physically and biologically meaningful way,” Lustig explains. “There has been a lot of trial and error about the type of flow rates we should be using, the type of nanoparticle concentrations, and the speed at which the nanoparticles should be sprayed.”

The results show that absorbent diapers that can stop coronavirus particles with equal or greater effectiveness than an N95 mask include those using terrycloth, quilted cotton, and flannel. The best water repellent layers to add in these suits involve non-woven polypropylene – the Lustig team tested OLY-Fun fabric – and materials made of polyester and polyaramid, a blend used in the fabric of lab coats.

PhD student Devyesh Rana measures the concentration of sprayed fluorescent nanoparticles (virus simulant) through tissue on glass slides in the Interdisciplinary Complex of Science and Engineering. Photos by Matthew Modoono / Northeastern University

The team also tested cotton coated with Scotchgard, a commercial fabric and padding protector that repels water. It’s one way to turn a fabric into a decent water repellent barrier, Lustig says.

“With many types of cotton, one or two coats won’t work,” he says. “But multiple coats will work, and if you have at least one or two hydrophobic coats, you’ll get pretty good protection.”

Scotchgard can help. But people shouldn’t breathe the spray directly and shouldn’t use it in layers of tissue that are closest to the mouth, Lustig says. The idea is to use Scotchgard if that’s the only option people have for a water repellent, spray it on the outer or middle layer of a mask and let it dry before putting it on.

Illustration by Gregory Grinnell / Northeastern University

Like virus droplets expelled by a person, water droplets carrying nanoparticles can accumulate on the surface of a material. This may give the impression that the particles will not pass through it. But the team’s tests have shown that a material’s absorbance alone doesn’t speak to its abilities to block viral-like particles.

When droplets accumulated on the surface of the materials the team tested, airflow modifications designed to mimic the breathing of a mask wearer helped the nanoparticles pass through.

“It’s a real possibility, because if you sneeze and it’s a big sneeze, or if you have some kind of wet cough, you can flood your mask,” Lustig explains, explaining that there are other ways. which a mask can get wet, such as when someone else’s sneezing or cough floods the outer layer of a mask.

“That’s the purpose of hydrophobic layers,” he says. “To make sure that aerosols don’t get all the way in if someone sneezes on your mask, that you don’t pick up this virus particle when your tongue touches the mask.”

Because of the effect breathing might have on the effectiveness of a face mask, Lustig says trying to change the way people breathe can also help people in situations where they are at greater risk. high to inhale the coronavirus.

“If someone just sneezed in front of you and they’re not wearing a mask, you’d better hold your breath as you walk past, or turn around to walk away before you start breathing heavily into your mask again.” . “, says Lustig.

The team began designing the experiment shortly after reading in an email that Michael Rosenblatt, chief medical officer at Lahey Hospital and Medical Center, was asking for help testing common fabric materials. that medical staff could use amid mask shortages in the US

The US military and the US Department of Agriculture have also experienced face mask shortages, and they have also used the team’s research, Lustig says.

“They needed science-based answers,” he says. “We realized that we would rather help rather than stand by. “

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