Nanothread filter forms barrier against coronavirus aerosols

A filter made from polymer nanothreads has been shown to capture 99.9 per cent of coronavirus aerosols compared to other forms of face coverings and air filters.

Left: A nanofibre filter that captures 99.9 per cent of coronavirus aerosols; Right: A highly magnified image of the polymer nanofibres (Image: Yun Shen)

The study, led by engineers at UC Riverside and The George Washington University, is said to be the first to use coronavirus aerosols for evaluating filtration efficiency in such masks and filters.

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“Previous studies have used surrogates of saline solution, polystyrene beads, and bacteriophages – a group of viruses that infect bacteria,” said corresponding author Yun Shen, a UC Riverside assistant professor of chemical and environmental engineering. The team’s findings have been published in Environmental Science & Technology Letters.

The study compared the effectiveness of surgical and cotton masks, a neck gaiter (or snood), and electrospun nanofibre membranes at removing coronavirus aerosols to prevent airborne transmission. The cotton mask and neck gaiter removed about 45 per cent-73 per cent of the aerosols. The surgical mask removed 98 per cent of coronavirus aerosols but the nanofibre filter was found to remove almost all the coronavirus aerosols, which have been identified as a major mechanism of COVID-19 virus transmission.

Efforts to curb aerosol spread of COVID-19 have focussed on minimising individual exposure and reducing the overall quantity of aerosols in an environment by asking people to wear masks and by improving indoor ventilation and air filtration systems.

To date, all studies during the pandemic on mask or filter efficiency have used other materials thought to mimic the size and behaviour of coronavirus aerosols. The new study improved on this by testing an aerosolised saline solution and an aerosol that contained a coronavirus in the same family as the virus that causes COVID-19, but only infects mice.

Shen and George Washington University colleague Danmeng Shuai produced a nanofibre filter by sending a high electrical voltage through a drop of liquid polyvinylidene fluoride to spin threads about 300nm in diameter. The electrospinning process created pores only a couple of micrometres in diameter on the nanofibre’s surfaces, which helped them capture 99.9 per cent of coronavirus aerosols.

The nanofiber technique is cost effective and could be used to mass produce nanofibre filters for personal protective equipment and air filtration systems. Electrospinning also leaves the nanofibres with an electrostatic charge that enhances their ability to capture aerosols, and their high porosity makes it easier to breathe wearing electrospun nanofibre filters.

“Electrospinning can advance the design and fabrication of face masks and air filters,” Shen said in a statement. “Developing new masks and air filters by electrospinning is promising because of its high performance in filtration, economic feasibility, and scalability, and it can meet on-site needs of the masks and air filters.”