Nose-hair-inspired air filters clean faster, last longer

Mucus in the nose plays a critical role in cleaning the air that’s headed toward our lungs. It coats nasal hairs, catching pollen and dust that would otherwise brush past. Now chemical engineers show they can apply the mucus model to manufactured air filters, such as those used in air conditioners. They coat filters with a liquid layer, a combination that captures more particles and holds them tighter than traditional bare filters, even when the air blows the other way (Nature 2025, DOI: 10.1038/s41586-025-09156-y).

Thin oil coatings often protect surfaces from ice and bacterial fouling. But those thin liquid coatings can also make a surface stickier because of the capillary force in the vertical direction, says Sanghyuk Wooh, a chemical engineer at Chung-Ang University. Think of glitter that falls on a wet tabletop. It easily moves with the liquid along the surface but is hard to remove from the table as long as the surface is wet.

Now imagine glitter falling on a net of wet fibers. That’s the idea behind Wooh and coworkers’ particle-removing oil-coated (PRO) filter. They first grafted polydimethylsiloxane (PDMS) molecules onto filter fibers and then sprayed silicone oil (also PDMS) over the filters, forming a stable thin film that sticks to and covers the fibers, like a thin oil sheen that stays in place.

They tried coating all sorts of filter fibers, from polyesters to cottons, and found that their liquid layer improved filtration efficiency by 10–30%. Plus, the PRO filter lasts longer because of how it holds particles. On bare filters, particles attach by stacking on top of each other in long, branching queues, one particle attached to the next. But those queues take up space and narrow filter pores. A PRO filter fiber holds crowded bunches of particles close to each fiber, keeping filter pores open longer and extending filter life.

In fact, in field tests that ran for 10–18 months at multiple locations in Seoul, they found the filters lasted two to three times as long as bare filters and saved about 25% in annual heating, ventilating, and air-conditioning (HVAC) operation costs.

Liquid-layer filters solve one more pesky filtration problem: particle redispersion. With most filters, blowing air back the other way loosens particles. This filter holds on to them. The group installed filters in an outdoor smoking area with wind blowing both directions. The bare filter lost whatever it caught with an off-direction gust. The PRO filter kept catching particles no matter the wind direction. “I think this can be a new paradigm of filtration” that takes advantage of existing wind, Wooh says.

That could mean that locations such as subway tunnels, construction sites, and train stations could add passive filtration to their air filtration systems. Wooh has patented the PRO filter in the US and South Korea and started a company called Wise and Yirop. His group is now working on a biodegradable version.

Caitlin Howell, a bioengineer at the University of Maine, says that because liquid is deformable, it’s “better at capturing particles than a solid would ever be.”

Xu Hou, a chemical engineer at Xiamen University, adds that “the PRO filter’s direction-dependent stickiness is a masterstroke” that achieves high filtration efficiency without the usual trade-off of shorter filter lifetime.