Abstract
The modeling of the viability decay of viruses in sessile droplets is addressed considering a droplet sitting on a smooth surface characterized by a specific contact angle. To investigate, at prescribed temperature, how surface energy of the material and ambient humidity cooperate to determine the virus viability, we propose a model which involves the minimum number of thermodynamically relevant parameters. In particular, by considering a saline water droplet (one salt) as the simplest approximation of real solutions (medium and natural/artificial saliva), the evaporation is described by a first-order time-dependent nonlinear differential equation properly rearranged to obtain the contact angle evolution as the sole unknown function. The analyses were performed for several contact angles and two typical droplet sizes of interest in real situations by assuming constant ambient temperature and relative humidity in the range 0–100%. The results of the simulations, given in terms of time evolution of salt concentration, vapor pressure, and droplet volume, elucidate some previously not yet well-understood dynamics, demonstrating how three main regimes—directly implicated in nontrivial trends of virus viability and to date only highlighted experimentally—can be recognized as the function of relative humidity. By recalling the concept of cumulative dose of salts (CD), to account for the effect of the exposition of viruses to salt concentration on virus viability, we show how the proposed approach could suggest a chart of a virus fate by predicting its survival time at a given temperature as a function of the relative humidity and contact angle. We found a good agreement with experimental data for various enveloped viruses and predicted in particular for the Phi6 virus, a surrogate of coronavirus, the characteristic U-shaped dependence of viability on relative humidity. Given the generality of the model and once experimental data are available that link the vulnerability of a certain virus, such as SARS-CoV-2, to the concentrations of salts or other substances in terms of CD, it is felt that this approach could be employed for antivirus strategies and protocols for the prediction/reduction of human health risks associated with SARS-CoV-2 and other viruses.
Highlights
As well known, the current pandemic events have rekindled the attention on the behavior of the virus diffusion and viability in several environmental conditions to envisage proper guidelines to prevent or somehow stop the contagion spreading
We model the evaporation of a sessile droplet of saline to approximate the solutions used in experiments given its close resemblance to the medium used in most viability experiments, its evaporation rates comparable to those of medium and saliva and for the analytical intractability of a complex solution such as natural saliva
We found that the common experiments are usually performed by placing a droplet containing various kinds of enveloped coronaviruses solution (1–50 μL) on flat surfaces, controlling the temperature and the relative humidity RH, extracting some samples at predefined time points and analyzing them via plaque assays
Summary
The current pandemic events have rekindled the attention on the behavior of the virus diffusion and viability in several environmental conditions to envisage proper guidelines to prevent or somehow stop the contagion spreading. By starting from these experimental evidences, in what follows, we propose a mathematical model of a spherical cap droplet encapsulating a model virus, which incorporates all the relevant thermodynamics aspects of interest, by so analyzing the dependence on RH and on the material surface characteristics (through the contact angle θ) of the virus viability, by, in particular, relating the evaporation of saline sessile droplets to a proper measure of the so-called cumulative dose, CD.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
