IIT-B researchers design a surface that makes coronavirus evaporate faster
Researchers at the Indian Institute of Technology-Bombay (IIT-B) have designed a surface that can expedite the evaporation of residual droplets carrying Sars-CoV-2, the virus that causes Covid-19, from surfaces.
According to the World Health Organisation, Covid 19 primarily spreads when small liquid particles are released into the air when a person infected with the virus coughs, speaks, sings or sneezes. The disease can also transmit via droplets settled on surfaces of objects, often known as fomite transmission. However, fomite transmission is now widely regarded as the least transmissible mode of spread of the virus.
When a person infected with Covid-19 coughs or sneezes, respiratory droplets containing the virus are released into the air. This is primarily how Covid-19 spreads. However, the disease can also transmit via droplets settled on surfaces of objects, often known as fomite transmission.
IIT-B researchers have proposed a way of designing surfaces for accelerating the evaporation of the residual droplets on surfaces by tuning surfaces’ wettability and creating geometric microtextures on them. Their paper titled— Designing antiviral surfaces to suppress the spread of Covid-19—was published in the Physics of Fluids letter of the peer-reviewed journal AIP Publishing on Wednesday.
The lifespan of the respiratory droplet on the surface determines how likely the surface is to spread the virus. While 99.9% of the droplet’s liquid content evaporates within a few minutes, a residual thin film that allows the virus to survive can be left behind. On some surfaces such as glass, the film can last up to four days and on plastic or stainless steel up to seven days.
Sanghamitro Chatterjee, Janani Srree Muralidharan, Amit Agrawal, and Rajneesh Bhardwaj — all researchers from IIT-B — had in the past shown that the survival time of the Covid-19 virus was correlated to the drying time of a respiratory droplet on an impermeable (non-porous) surface along with a residual film left on it by the droplet. In a follow-up study in February, they demonstrated how the mass loss of a respiratory droplet and the evaporation mechanism of a thin liquid film is different for porous and non-porous surfaces.
In their new study, they’ve found that an optimally designed surface will make a viral load decay rapidly, rendering it less likely to contribute to the spread of viruses.
“We’ve extended our findings from the previous studies to design a surface that can make droplets evaporate faster. It works just like a lotus leaf. The surface of a lotus leaf has microscopic pillars on them that make the water droplets roll-off. Bioinspired from lotus leaf, the proposed antiviral surface has microscopic pillars on them,” said co-author of the study Rajneesh Bhardwaj, associate professor of Mechanical Engineering, IIT-B. They designed microtextures or microscopic pillars on surfaces to accelerate the evaporation of liquid.
“In terms of physics, the solid-liquid interfacial energy is enhanced by a combination of our proposed surface engineering. The pressure inside the liquid film increases and helps it to dry quickly,” said Chatterjee, lead author and a postdoctoral fellow in the mechanical engineering department.
The researchers tried a combination of surface microtextures to determine the most optimal one. “Continuously tailoring any one of these parameters wouldn’t achieve the best results,” said Agrawal, institute chair professor at the department of mechanical engineering and co-author of the paper.
“We also propose a design methodology and provide parameters needed to engineer surfaces with the shortest virus survival times,” said Muralidharan, an assistant professor in the department of mechanical engineering.
The researchers discovered that surfaces with taller and closely packed pillars, with a contact angle of around 60 degrees, show the strongest antiviral effect or shortest drying time. “This study lays the foundation for fabricating antiviral surfaces that will be useful in designing hospital equipment, medical or pathology equipment, as well as frequently touched surfaces, like door handles, smartphone screens, or surfaces within areas prone to outbreaks,” said Bharadwaj.
“Since we analysed antiviral effects by a generic model independent of the specific geometry of texture, it’s possible to fabricate any geometric structures based on different fabrication techniques — focused ion beams or chemical etching — to achieve the same outcome,” Bharadwaj added.
“This study helps understand how nanosurfaces work and how they can be used to prevent the spread of Covid-19. These surfaces can be used at healthcare facilities,” said Shyamprasad Karagadde, associate professor, department of mechanical engineering, IIT-B, who was not a part of the study.