The pandemic has led to N95 masks quickly becoming one of the world's most sought-after resources as essential workers burned through billions of them. New research could lead to an N95 that you can recharge rather than throw away — or even one that continuously tops itself up for maximum effectiveness.
The proposed system, from researchers at Technion-IIT in Israel and the Tata Institute of Fundamental Research in India, is not one of decontamination, as you might expect. Instead, it focuses on another aspect of N95 masks that renders them less effective over time.
N95s use both mechanical filtering, in which particles are caught in a matrix of microscopic fibers, and electrostatic filtering, in which particles are attracted to surfaces that carry a static charge. It's like the old trick where you rub a balloon on your head and it sticks — but at the scale of microns.
The combination of these two methods makes N95 masks very effective, but the electrostatic charge, like any charge, dissipates after time as air and moisture pass over it. While decontamination via UV or high temperature may help keep the mechanical filter from becoming a tiny petri dish, they do nothing to restore the electrostatic charge that acted as a second barrier to entry.
In a paper published in the journal Physics of Fluids, Dov Levine and Shankar Ghosh (from Technion and Tata, respectively) show that it's possible to recharge an N95's filter to the point where it was close to off-the-shelf levels of efficacy. All that's needed is to place the filter between two plate electrodes and apply a strong electric field.
"We find that the total charge deposited on the masks depends strongly on the charging time... with the pristine value almost reattained after a 60 min charge at 1000 V," write the researchers in their paper.
A self-charging N95 mask prototype
It's unlikely that healthcare workers are going to be disassembling their masks after every shift, though. While a service and special mask type could (and if it's effective, should) be established to do this, the team also explored the possibility of a mask with a built-in battery that recharges itself constantly:
A solution that can help replenish the lost charge on the masks in real time would be desirable. In this section, we provide a proof-of-concept method of keeping the masks charged, which comes as a logical extension of our recharging method.
We tested a technique by which the filter material maintains its charge and thus its filtration efficiency... Since the currents required are extremely small, a large battery is not required, and it is possible that a small compact and practical solution may be feasible.
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The image above shows a prototype, which the team found to work quite well.
Of course it's not quite ready for deployment; IEEE Spectrum asked Peter Tsai, the creator of the N95 mask, for his opinion on it. He suggested that the team's method for testing filtration efficacy is "likely questionable" but didn't take issue with the rest of the study.
Though it won't be in hospitals tomorrow or next week, the team notes that "crucially, our method can be performed using readily available equipment and materials and so can be employed both in urban and rural settings." So once it's thoroughly tested it's possible these rechargeable masks could start showing up everywhere. Let's hope so.