Using face masks has become necessary and even mandatory in many parts of the world to reduce the spread of the novel coronavirus. Virus transmission is believed to take place via respiratory droplets resulting from sneezing and coughing, which can be at least partially prevented by the use of masks.

This has caused a global spike in the demand for face masks and the decision to limit the sale of some models, especially the N95 mostly used by health workers. Still, shortages have been reported, leading to many using the same mask repeatedly, with many risks implied.

In this context, researchers have come up with a potential solution. They developed a membrane that can be attached to a standard N95 mask and be replaced when needed. What’s more, the filter has a smaller pore size than the actual masks, blocking more virus particles.

An N95 mask offers more protection than a surgical mask does because it can filter out both large and small particles suspended in the air. As the name indicates, the mask is designed to block 95% of very small particles. Some masks have valves that make them easier to breathe through.

Detachable filters for the most advanced face masks

Muhammad Mustafa Hussain from the University of California, Berkeley, California, and colleagues developed a silicon-based, porous template using lithography and chemical imprint. They placed it over a polyimide film and used a process called reactive ion etching to make pores in the membrane. Then, they peeled off the membrane, which can be attached to the mask.

To make sure that the membrane was breathable, the researchers measured the airflow rate through the pores. They found that for pores tinier than 60 nanometers (in other words, smaller than SARS-CoV-2), the pores needed to be placed a maximum of 330 nm from each other to achieve good breathability.

“The porous membrane is based on a naturally hydrophobic polymer such that the droplets that come into contact with the mask will roll and slide over the mask due to the large inclination angle of the membrane when worn on the face mask,” the researchers wrote.

The finding follows other recent studies that have been trying to provide answers to the mask’s scarcity. For instance, a team of CalTech researchers proposed a new way to clean masks, safely, efficiently, and in an inexpensive way — using ethanol instead of isopropyl alcohol.

In the US, the Centers for Disease Control and Prevention (CDC) recommended early this month that citizens should wear “non-medical, cloth masks” to help prevent the spread of the coronavirus. Previously, the CDC had recommended that only those with COVID-19 symptoms wear masks.

The study was published in the journal of the American Chemical Society.