Airborne drying of respiratory droplets exposes fewer viral particles than on surfaces
Airborne drying of respiratory droplets exposes fewer viral particles than on surfaces lead image
COVID-19 spreads via respiratory droplets emitted during a breath, sneeze or cough. These droplets soon break apart and desiccate to form aerosols and small airborne dried nuclei that contain infectious virions. Understanding the dynamics of these changes and their effect on the distribution of viral particles could yield insight into how COVID-19 spreads. Basu et al. illuminated this behavior by imaging isolated model respiratory droplets held midair with acoustic levitation.
The group found airborne droplets hold the vast majority of virions in the bulk, while in sessile droplets – those that have attached to a surface – 80-90% of the particles migrate to the edges and become exposed.
They also found desiccated particles retain just 20-30% of their diameters, an effect consistent across a variety of initial sizes and conditions.
The group used a 1% by weight NaCl in water solution to model mucosalivary fluids. To mimic virions, they used polystyrene nanoparticles, which share similarly low motility and rotational diffusivity.
Using these virus-like particles, “we demonstrated how the virions would distribute in such nuclei, which is fundamentally relevant to virologists to ascertain virus survivability in aerosols,” said author Saptarshi Basu.
The team used laser and flow visualization to image the droplets as the liquid evaporates and the remaining precipitate breaks apart.
“Most of the previous studies on pathogens in respiratory droplets were performed with sessile droplets, whose drying dynamics [are] very different from airborne droplets,” said Basu. “Usage of an acoustic levitator to suspend a respiratory droplet in a contact free environment is the closest one can get to replicate and probe the evaporation and desiccation dynamics of respiratory droplets.”
Source: “Insights on drying and precipitation dynamics of respiratory droplets from the perspective of Covid-19,” by Saptarshi Basu, Prasenjit Kabi, Swetaprovo Chaudhuri, and Abhishek Saha, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/5.0037360 .
