A new study found that silk could be a solution for COVID-19 prevention. Silk, as a component of face mask, might be better than cotton or synthetic materials.
The potential of silk-made face masks was investigated by biologists at the University of Cincinnati (UC), a US public research university. They confirmed that face masks made of silk were better compared to other fabric. This could enable startups of silk face masks. The advantages of silk were linked to copper and water repellency. They published their findings in PLOS One.
The Role of Face Mask in COVID-19 Pandemic
When the pandemic started, the world faced a major shortage in the supply of surgical masks. This limited the availability of medical-grade face masks for healthcare professionals. Eventually, the public used cloth face masks to avoid contracting COVID-19. Months later, major health organizations finally recognized that cloth masks are better than no masks at all. They simply limit medical-grade face masks among healthcare professionals, people with chronic illnesses, and people with respiratory symptoms.
According to Statista, a German portal for statistics, the effectiveness of face masks depends on the context. Cloth masks are generally unproven in various settings. But it can decrease droplet ejection and exhalation by wearers. It may also increase the physical distancing awareness of wearers. Medical masks are intended to protect others from wearers. This is because medical masks significantly reduce the wearer's ejection of droplets. Filtration masks are hardcore devices due to the high reduction of solid and liquid aerosols, and nanoparticles. Though, wearers may experience slight breathing difficulty.
In a Statista COVID-19 Barometer, a survey that ended on May 31, 2020, 66% of respondents in the US, 52% in Germany, and 20% in the UK wore face masks when going outside. Those figures were higher than 39% in the US, 16% in Germany, and 13% in the UK in the survey results that ended on April 12, 2020. In China, the rates were 81% in the week ending on April 12 and 78% in the week ending on May 31.
Meanwhile, Spain had the highest rate of face mask use in Europe, as of June 28, 2020. The countries always wearing a face mask outside was 84.1% in Spain, 83.1% in Italy, 63.1% in Germany, 53.3% in France, and 19.3% in the UK. The next five countries had rates for always wearing a face mask outside at 9.4% in the Netherlands, 3.6% in Norway, 2.4% in Sweden, 1.9% in Finland, and 1.6 in Denmark.
Silk as Material for Cloth Masks
Cloth masks that protect oneself from COVID-19 can be made from different materials. The most common ones are made of cotton. But there are products composed of other fabric, including synthetic. Despite the lower effectiveness of cloth masks than surgical masks, health experts recommend them for typical situations. At least, cloth masks act as a barrier between the wearers and liquid droplets in the air.
At UC, biologists investigated what fabric would be better on cloth masks. They examined if the type of fabric particularly mattered on filtering particles in the air. They found one with significant effect: silk. Silk could provide higher protection than cotton or synthetic fabric. The material was next to N95 respirators and medical-grade surgical masks, in terms of performance. However, the best silk could only be obtained from caterpillars.
“Silk has been with us for a while - since the days of the Silk Road. It’s not a new fabric, yet now we’re finding all these new uses for it,” said Patrick Guerra, the corresponding author of the study and assistant professor of biology at UC.
Among metals, copper is highly valued due to its excellent thermal and electrical conductivity. Medically, copper is known for its antimicrobial properties. Studies have shown that copper naturally destroys a wide range of microorganisms, including methicillin-resistant Staphylococcus aureus, adenoviruses, and influenza A virus. Because of the properties, certain regulatory entities approved antimicrobial copper products.
Presently, many medical frontliners use both N95 and surgical masks. Surgical masks are worn to protect N95 masks, which increase longevity. The result extends the availability of N95 masks and reduces waste per day. But the waste from masks in healthcare is inevitable. There is a great need for effective masks that can be reused to counter the environmental consequences.
Guerra's wife Evelyn, a physician, suggested silk as a good choice for covering the exterior of N95. Cloth masks made of silk could perform similar to medical-grade masks. To test silk's performance, the team obtained silk, cotton, and polyester fabric. They tested these materials in repelling water, which represented liquid droplets suspended in the air. Silk tested superior in repelling water than cotton and polyester. Results showed the silk absorbed water at a slower rate, compared to the other two fabrics.
Next, the study's first author Adam Parlin prepared a Styrofoam head and a silk mask. This test compared silk masks to other face masks in repelling aerosolized droplets. The silk mask could impede aerosolized droplets and water better than cotton, polyester, or other synthetic fabric. The team concluded that silk could be an excellent fabric for face masks. Not only it could be washed and reused, but its performance could be increased by tweaking the number of silk layers.
The silk in the study is the mulberry silk, created by mulberry silkworm Bombyx mori. A single silkworm can spin silk for 72 hours nonstop at a specific stage of their life cycle. Copper is included in the silk they produced. This is because the silkworm eats mulberry leaves that contain copper. As a result, the silk is infused with the metal.
Biologists are now planning for a follow-up study. Their goal is to determine how long SARS-CoV-2 can survive after being exposed to copper. They also need to compare the pathogen's survivability on copper to other materials used to make cloth masks. If SARS-CoV-2 cannot withstand copper, it will indicate silk's potential in COVID-19 prevention.