By reusing common ingredients in hair conditioner , scientists have designed an inexpensive, transparent coating that can turn surfaces like windows and ceilings into sticky pads to trap airborne aerosol droplets. magazine ‘ Chem ‘.
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“In the face of a pandemic, we have to proactively harness all the different layers of defense mechanisms, including physical barriers, ” says corresponding author Jiaxing Huang, professor of materials science and engineering at Northwestern University in the United States . “At the end of the day, these viruses must travel through physical space before reaching people and eventually infecting them.”
The main way of spreading respiratory diseases like COVID-19 is through respiratory fluids emitted when an infected person speaks, sneezes or breathes. These virus-containing fluids include large droplets and fine aerosols that are especially difficult to control and remove from the air.
When colliding with a surface, aerosol droplets can easily bounce back and become airborne again . As a materials scientist, Huang wanted to help fight the pandemic in some way. He brought together several researchers from his lab, such as Drs Zhilong Yu and Murat Kadir, and another stay-at-home student, Yihan Liu, to brainstorm ideas.
Finally, they came up with the idea of converting PAAm-DDA , a polymer commonly used in hair and cosmetic products to retain moisture, into a surface coating . The coating they developed is hydrophilic , so it can capture droplets that contain pathogens and prevent them from bouncing off surfaces. “There are many indoor environmental surfaces that are hardly touched , such as the parts of the wall closest to the floor and ceiling,” Huang says, where their coating could be applied.
This was the simulated experiment
Huang and his team lined a Plexiglas partition and tested its droplet capturing ability. The team first sprayed the barrier with an aerosol vapor, generated by a handheld facial steamer, to simulate the fine respiratory aerosols emitted when speaking.
By analyzing escaping droplets that land on a silicon wafer, they can estimate the coating’s ability to trap incoming aerosol droplets. Compared to an uncoated barrier, the coating captured almost all aerosols and barely let any of them escape .
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They then sprayed salt water on the Plexiglas to simulate the large droplets released by coughing and sneezing, and found that the coating also dramatically reduced the number of splattered droplets. In the simulated experiment, the number of droplets that escaped from the Plexiglas barrier was reduced by 80% .
In the past, scientists have designed water trapping agents that target mostly large water droplets for use in applications such as extracting water from the air in the desert or in applications in agriculture . “We did an extensive literature search, but we didn’t find much work to capture aerosol droplets. Perhaps there was not a great need for these types of coatings to trap aerosols before the pandemic,” Huang says.
Applicable to various materials
To make the product applicable to more types of surfaces, the team added another common cosmetic ingredient, called APG, to the coating. They tested it on materials such as concrete, wood, metal, glass and textiles, which are typical surfaces of interior spaces . Huang says more ingredients can be added to give the coating additional functions, such as the copper ion as a disinfectant or pigment particles for coloring.
“What we want is to provide scientific evidence for a future public health capacity.”
Although human experiments must be pre-approved by some regulatory bodies and are outside the scope of the study, the team calculated the number of respiratory droplets released by people who speak loudly and continuously in a typical office environment in interiors .
Their calculation shows that the threshold of the coating before saturating with droplets is about 7 to 10 orders of magnitude higher than what would be emitted in the office setting. Also, if necessary, the coating can be easily cleaned with water and reapplied .
“We understood that the current pandemic may end before this concept is applied,” he says. “What we want is to provide scientific evidence for a future public health capacity . It may or may not be used now. But next time, when it occurs. an outbreak like this, I think we will be better equipped, “concluded the researcher.