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Microscopic images reveal the science and beauty of face masks

Studying tissues at a very high magnification helps determine how some masks filter particles better than others. And the close-ups reveal an invisible beauty of worldly objects that have now become an essential part of life around the world.

While scientists continue to demonstrate how effective masks can be in slowing the spread of the new coronavirus, especially when they fit well and are used correctly, some have adopted microscopic approaches (SN: 2/12/21).

"Embedded in microscale textures are clues as to why materials have multiple properties," says Edward Vicenzi, a microanalysis expert at the Smithsonian's Museum Conservation Institute in Suitland, MD. "Unveiling that evidence turns out to be a fun job."

Prior to the pandemic, Vicenzi spent his days observing meteorites, rocks, and other museum specimens under a microscope. But in March 2020, as the COVID-19 pandemic progressed, he and colleagues at the National Institute of Standards and Technology in Gaithersburg, Maryland, felt a strong desire to help recover the virus. So they started studying materials to cover their face.

Cotton flannel: In this view of the fabric a network of cotton fibers “glides” over a woven surface. This chaotic arrangement offers cotton flannel fibers additional opportunities to pick up particles as they flow through the fabric. E.P. Vicenzi / Smithsonian’s Museum Conservation Institute and NIST

microscopic image of a polyester cotton blend fabric

Polyester-cotton blend: Crumpled (pale) natural cotton fibers contrast with almost identical (blue) polyester fibers in this false color image. Polyester fibers are highly organized, mostly straight and smooth, so they are less effective than cotton fibers just for trapping particles at the nanometer scale. E.P. Vicenzi / Smithsonian’s Museum Conservation Institute and NIST

ray tissue microscope image

Rayon: Like the patterns observed in the rigatoni paste, the grooves run along the length of the ray fibers. Unlike cotton flannels, rayon has no apparent webl-shaped structures formed from raised fibers, which facilitates the movement of particles from one side of the synthetic fabric to the other. E.P. Vicenzi / Smithsonian’s Museum Conservation Institute and NIST

microscope image of wood flannel fabric

Flannel of the: Lives in cross section, these fibers look like a whirlwind of hurricanes. Wool flannel can also form fiber bands that block particles, but those bands are not as effective as those of a percent cotton, the researchers found. E.P. Vicenzi / Smithsonian’s Museum Conservation Institute and NIST

microscope image of a mask n95

Mask n95: In an N95 mask (false cross-sectional view), a thin outer layer (top) and a thick inner layer (bottom) sandwich a filtration layer (purple), which traps smaller particles. The multilayer set made of plastic melts and melts into a fabric similar to what makes N95 filter particles better than fabric masks, even cotton ones. E.P. Vicenzi / Smithsonian’s Museum Conservation Institute and NIST

Using a scanning electron microscope, Vicenzi and colleagues examined dozens of materials, including coffee filters, pillowcases, surgical masks, and N95 masks. In 2020, the team discovered that N95 respirators are the most effective at providing protection against aerosols such as those traveled by SARS-CoV-2, the virus that causes COVID-19. And the researchers reported that synthetic fabrics, such as chiffon or rayon, do not trap as many particles as well-woven cotton strips.

Microscopic textures can explain the ability of each tissue to filter aerosols. The random nature of cotton fibers – with their wrinkled texture and complex shapes like twists, folds and folds – will likely allow cotton to trap more particles at the nanometer scale than other fabrics, Vicenzi says. In contrast, polyester fabrics have highly organized fibers, mostly straight and smooth, which makes them less efficient as face masks.

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Cotton strips also provide extra protection by absorbing moisture from the breath, Vicenzi and colleagues report on March 8 at ACS Applied Nano Materials.

“Since cotton loves water, it swells in humid environments and that makes it harder for particles to make their way through a mask,” says Vicenzi. In contrast, polyester and nylon masks "repel water from breathing, so there is no additional benefit."

Through his work, Vicenzi explored the invisible world of face-covering materials. Some textiles remind you of foods, such as ray fibers that resemble the texture of rigatoni pasta. Others, like wool, remind him of atmospheric patterns like the whirlwind of a hurricane.

Vicenzi plans to keep a close eye on the face masks. And he hopes his research will help people decide how best to protect themselves and others during the COVID-19 pandemic. “It’s good to use an effective material for a mask if you can,” he says. "However, wearing any mask compared to any makes the biggest difference in slowing the spread of pathogens."

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