Role of mucin in controlling evaporation and hygroscopic behavior of human respiratory droplets and potential implications for spreading of pathogens

The transmission of respiratory pathogens through aerosolized expiratory secretions, in the form of droplets and aerosols, represents a primary route for the spreading of infectious respiratory diseases, including COVID-19. Investigating the droplet micro-environment occurring under different conditions to understand the infectivity of pathogens carried by droplets holds significant implications for controlling the dissemination of airborne diseases. Here, we conducted measurements of the evaporation and hygroscopic growth of levitated artificial human saliva droplets using an electrodynamic balance. These measurements were complemented with the characterization of the morphology of evaporated droplet residuals using a scanning electron microscope and light scattering patterns, providing a further understanding of the underlying mechanisms of the relative humidity-dependent inactivation of viruses. Results showed that saliva droplets exhibited a complex morphology change behavior during evaporation at RH below 45%. The presence of mucin slightly retarded the evaporation rate and significantly impeded the water uptake process of saliva droplets. ... mehrThis phenomenon was attributed to the possible formation of a mucin-enriched layer on the surface of the saliva droplets during the evaporation process. These findings emphasize the significant role of mucin in affecting the properties of saliva droplets during evaporation and rehydration, thereby potentially influencing the persistence of pathogens.