New replaceable, more efficient filter for N95 masks developed

Researchers have developed a more efficient membrane filter that can be attached to a regular N95 mask and replaced when needed.

The filter has a smaller pore size than normal N95 masks, potentially blocking more virus particles, according the researchers from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia.

Since the outbreak of COVID-19, there's been a worldwide shortage of face masks -- particularly the N95 ones worn by health care workers, they said.

Although these coverings provide the highest level of protection currently available, they have limitations, the researchers noted in the journal ACS Nano.

N95 masks filter about 85 per cent of particles smaller than 300 nm, they said.

The researchers noted that SARS-CoV-2, the coronavirus that causes COVID-19 is in the size range of 65-125 nanometres (nm), so some virus particles could slip through these coverings.

Due to shortages, many health care workers have had to wear the same N95 mask repeatedly, even though they are intended for a single use.

To help overcome these problems, Muhammad Mustafa Hussain and colleagues wanted to develop a membrane that more efficiently filters particles the size of SARS-CoV-2 and could be replaced on an N95 mask after every use.

The researchers first developed a silicon-based, porous template using lithography and chemical etching.

They placed the template over a polyimide film and used a process called reactive ion etching to make pores in the membrane, with sizes ranging from 5-55 nm.

The researchers then peeled off the membrane, which could be attached to an N95 mask.

To ensure that the nanoporous membrane was breathable, the researchers measured the airflow rate through the pores.

They found that for pores tinier than 60 nm, the pores needed to be placed a maximum of 330 nm from each other to achieve good breathability.

The hydrophobic membrane also cleans itself because droplets slide off it, preventing the pores from getting clogged with viruses and other particles, according to the researchers.