This 3D image (taken with laser confocal microscopy) shows crater-like features generated by the captured droplets. Image: Northwestern University.
This 3D image (taken with laser confocal microscopy) shows crater-like features generated by the captured droplets. Image: Northwestern University.

Although plexiglass barriers are seemingly everywhere these days – between grocery store lanes, around restaurant tables and towering above office cubicles – they are an imperfect solution to blocking the transmission of viruses such as SARS-CoV-2.

Instead of capturing virus-laden respiratory droplets and aerosols, plexiglass dividers merely deflect droplets, causing them to bounce away but remain in the air. To enhance the function of these protective barriers, researchers at Northwestern University have developed a new transparent material that can capture droplets and aerosols, effectively removing them from the air.

As the researchers report in a paper in Chem, this material is a clear, viscous liquid that can be painted onto any surface, including plastic, glass, wood, metal, stainless steel, concrete and textiles. When droplets collide with the coated surface, they stick to it, get absorbed and dry up. The coating is also compatible with antiviral and antimicrobial materials, allowing sanitizing agents such as copper to be added to the formula.

"Droplets collide with indoor surfaces all the time," said Northwestern's Jiaxing Huang, the paper's senior author. "Right now, plexiglass dividers are deviating devices; they deflect droplets. If a surface could actually trap droplets, then every single droplet effectively removed from indoor air would be a successful elimination of a potential source of transmission."

In the study, the researchers found that even when they bombarded surfaces with aerosol droplets – at orders of magnitude higher concentrations than typical for an indoor environment – the coated surfaces still captured three times more aerosol droplets than uncoated surfaces.

Huang is a professor of materials science and engineering in Northwestern's McCormick School of Engineering. Zhilong Yu, Murak Kadir and Yihan Liu – all members of Huang's laboratory – co-authored the paper. The team embarked on this project during the stay-at-home order at the beginning of the COVID-19 pandemic.

The main ingredient in the Northwestern team's material is a polyelectrolyte polymer that is commonly used in a wide variety of cosmetic products. When applied with a blade or brush, the resulting formula yields uniform and conformal coatings on a broad range of indoor surfaces without damaging or discoloring the original material.

Huang's team found that the surfaces remained transparent and haze-free even when doused with droplets. If used on plexiglass barriers, the coated surfaces would not need to be cleaned more frequently than uncoated surfaces.

Most infectious diseases spread through respiratory droplets and aerosols, which humans release constantly when talking, laughing, singing and exhaling. Because the coating is so versatile, Huang imagines that it could be used on plexiglass barriers and face shields as well as on no-touch or low-touch surfaces, such as walls or even curtains, to eliminate droplets from the air.

"There are massive areas of indoor surfaces that are barely touched by people or pets. If we repurposed these 'idling' surfaces to capture respiratory droplets, then they could become functional 'devices' to help reduce air-borne transmission of infectious diseases," Huang said. "Surface-trapped pathogens can then be readily inactivated over time, which can be accelerated by pre-applied sanitization ingredients. They also can be removed during routine cleaning."

While Huang says that face masks are an irreplaceable public health tool to help prevent the spread of infectious droplets, he believes that trapping droplets on surfaces could be another effective tool.

"In a computer game, for example, you don't want to walk into a battlefield with only one piece of armor," he said. "It makes sense to leverage multiple layers of defense."

This story is adapted from material from Northwestern University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.