Abstract
To evaluate the role of common substrates in the transmission of respiratory viruses, in particular SARS-CoV-2, uniformly distributed microdroplets (approx. 10 µm diameter) of artificial saliva were generated using an advanced inkjet printing technology to replicate the aerosol droplets and subsequently deposited on five substrates, including glass, polytetrafluoroethylene, stainless steel, acrylonitrile butadiene styrene and melamine. The droplets were found to evaporate within a short timeframe (less than 3 s), which is consistent with previous reports concerning the drying kinetics of picolitre droplets. Using fluorescence microscopy and atomic force microscopy, we found that the surface deposited microdroplet nuclei present two distinctive morphological features as the result of their drying mode, which is controlled by both interfacial energy and surface roughness. Nanomechanical measurements confirm that the nuclei deposited on all substrates possess similar surface adhesion (approx. 20 nN) and Young's modulus (approx. 4 MPa), supporting the proposed core–shell structure of the nuclei. We suggest that appropriate antiviral surface strategies, e.g. functionalization, chemical deposition, could be developed to modulate the evaporation process of microdroplet nuclei and subsequently mitigate the possible surface viability and transmissibility of respiratory virus.
Highlights
Transmission of respiratory viruses can take place in different modes, either directly via contact between individuals, indirectly via commonly touched objects or surfaces, or directly through the air in the form of large droplets or small aerosols [1]
We suggest that appropriate antiviral surface strategies, e.g. functionalization, chemical deposition, could be developed to modulate the evaporation process of microdroplet nuclei and subsequently mitigate the possible surface viability and transmissibility of respiratory virus
One of the early studies suggested that SARS-CoV-2 remains viable in aerosols for at least 3 h, and that SARS-CoV-2 is more stable on plastic and stainless steel (SS) than on copper and cardboard [3], which highlighted the unique role of common surfaces in virus transmission during the pandemic
Summary
Transmission of respiratory viruses can take place in different modes, either directly via contact between individuals, indirectly via commonly touched objects or surfaces, or directly through the air in the form of large droplets or small aerosols [1]. There have been compelling arguments that the transmission of SARS-CoV-2 after touching surfaces should be considered as relatively minimal [5], given that it is improbable that an infected person coughs or sneezes on a surface (with sufficient quantity of infectious virus), and someone else touches that surface shortly after (within 1–2 h) [6]. This rationale is sound and sensible, on the assumption that surface transmission takes place via a large quantity of respiratory fluid and that the virus would be inactivated beyond the timeframe suggested. The likelihood of surface transmission is no longer as significant as perceived at the initial stage of the pandemic, the possible presence of infectious virus on solid substrates, in particular on high-touch environmental surfaces, could have significant implications for both social and healthcare practice
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