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The pandemic has led to N95 masks rapidly becoming one of the world’s most sought-after resources, as essential workers consumed billions of them. New research could lead to an N95 that you can reload rather than pull, or even one that continually recharges for maximum effectiveness.
The proposed system, from researchers at the Technion-IIT in Israel and the Tata Institute for Fundamental Research in India, is not decontamination, as might be expected. Instead, it focuses on another aspect of N95 masks that makes them less effective over time.
N95s use both mechanical filtering, in which the particles are trapped in a matrix of microscopic fibers, and electrostatic filtering, in which the 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 on the micron scale.
The combination of these two methods makes N95 masks very effective, but electrostatic charge, like any charge, dissipates over time as air and moisture pass over it. While decontamination via UV or high temperature can help prevent the mechanical filter from turning into a small Petri dish, they do nothing to restore the electrostatic charge that acted as a second barrier to entry.
In an article published in the journal Physics of Fluids, Dov Levine and Shankar Ghosh (from Technion and Tata, respectively) show that it is possible to recharge an N95 filter to the point where it was close to standard efficiency levels. All that is needed is to place the filter between two plate electrodes and apply a strong electric field.
“We found that the total charge deposited on the masks is highly dependent on charge time … with the pristine value almost regained after a 60 minute charge at 1000 V,” the researchers write in their paper.
A prototype self-loading N95 mask
However, healthcare workers are unlikely to dismantle their masks after each shift. While a special mask type and service could be established (and if effective, it should) to do this, the team also explored the possibility of a mask with a built-in battery that is constantly recharged:
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 for keeping skins loaded, which is presented as a logical extension of our reload method.
We tested a technique by which the filter material maintains its charge and therefore its filtration efficiency … Since the required currents are extremely small, a large battery is not required, and it is possible that a small compact and practical solution is feasible.
The image above shows a prototype, which the team found works quite well.
Of course, it is not ready for implementation; IEEE Spectrum asked Peter Tsai, the creator of the N95 mask, for his opinion on this. He suggested that the team’s method of testing the effectiveness of the filtration is “probably questionable,” but had no problems with the rest of the study.
Although he will not be in hospitals tomorrow or next week, the team notes that “crucially, our method can be performed using readily available equipment and materials, and therefore can be used in both urban and rural settings.” So once it’s been thoroughly tested, these rechargeable skins may start popping up everywhere. Hopefully.
