Polyimide membrane allows re-use of N95 respirators

Engineers in Saudi Arabia have fabricated a polyimide membrane to turn the N95 respirator into a reusable mask for protection against COVID-19.

N95 respirator
The membrane is attached to the outside of an N95 respirator and is removed and replaced after use (© 2020 American Chemical Society)

The N95 respirator is a single-use, tight-fitting, surgical-grade mask that filters 95 per cent of airborne particles. World health bodies and governments recommend their use only by healthcare professionals as they are in short supply.


Electrical engineer Muhammad Mustafa Hussain and his team at KAUST (King Abdullah University of Science and Technology) are said to have repurposed the N95 respirator by fabricating an attachable membrane that can be replaced after a single use. The new design facilitates reuse of the N95 mask, saving costs, resources and broadening its availability. The team’s advance is described in ACS Nano

Importantly, it could also improve the mask’s filtration efficiency for SARS-CoV-2, which causes COVID-19. Pores in N95 masks are around 300nm in size, while the SARS-CoV-2 virus is significantly smaller at 65 to 125nm.

According to KAUST, the team’s approach facilitates the design of ultrathin polymeric membranes that are hydrophobic and have pore sizes as small as 5nm. The method first involves etching funnel-shaped pores into a silicon-based template, producing an array of 90 x 90nm squares on one side and 5 to 55nm-sized pores on the other.

“The etching method controls the distances between the pores and overcomes the problem of randomly spaced and oriented pores found in polymeric, nanoporous membranes developed by other researchers until now,” Hussain said in a statement.

The template pattern is then etched on to a 10 micrometre-thick polyimide film that is removed from the template and can be attached to an N95 respirator.

The team’s theoretical calculations show that their repurposed N95 mask conforms to the breathability standards set out by the United States National Institute for Occupational Safety and Health.

“We are now working with commercial partners to further optimise our mask’s breathability and filtration efficacy,” says KAUST postdoc and the study’s first author, Nazek El-Atab.