ABSTRACT
Despite the gradual return to pre-pandemic conditions, the spreading of COVID-19 (SARS-CoV-2) left several open issues. Nowadays it is know that airborne infections, including COVID-19, are conveyed by particles having the size of >5 μm (droplets) and <5 μm (droplets nuclei), ejected by coughing and sneezing [1]. While droplets undergo to dehydration and precipitation, droplet nuclei persist in air for long time after their ejection, contributing to infection spreading. Actual prevention strategies are based on non-pharmaceutical interventions act to reduce droplets diffusion and spacing from Personal Protective Equipment, such as facial masks, and social distancing measure. Nevertheless, for the new endemic phase of COVID-19 the development of new strategies for airborne infections' containment becomes unavoidable. In this project, we propose a new device for the suppression of Airborne Viral Aerosols designed to work in situations with constrained geometries (e.g. public transportation, offices, waiting rooms etc.) not allowing social distancing. The device, devised to perform photokilling of viral aerosols in air in presence of humans, has its core in an UV illumination system operating at 222 nm. It is know from literature that UV radiation alters the genetic material of viruses and bacteria whose maximum absorption wavelengths are in the far-UV range (UVC, 100-280 nm), the most effective for sterilization [2]. Differently from the operative wavelength of most commercial systems (254 nm), the higher tissue absorption prevents the 222 nm radiation to travel over the very first epidermal layers [3] constituting a minor health risk for applications in presence of people. The device combines the UV illumination system with a vertical flux of air that conveys exhaled particles to the light source and controls humidity and temperature, crucial parameters for virus diffusion. After its development, the device prototype will be tested in model experiments. Initially, its safety will be verified by monitoring in particular the UVC-induced ozone production. Then, in vitro photokilling experiments will be performed in two steps: (i) on a layer of immobilized SARS-Cov-2 virus act to obtain optimal UV doses for an effective sterilization;(ii) on SARS-Cov-2 aerosol models. For this last experiment, a model viral aerosol miming the characteristics of cough and sneeze particles will be preliminary studied and supported by synthetic data to characterize the optical properties of the reference scenario. The resulting information will be crucial for the final design of the device itself. As a last step, we will test the device in in vivo experiments. An air flux, harvesting exhaled air by infected mice, will be illuminated by the device and will be sent to healthy mice. Finally, the infectiveness of exhaled air after the UV treatment will be evaluated, providing more information for further applications in the presence of humans.
ABSTRACT
The Covid-19 epidemic has been the most consequential global health crisis since the era of the influenza pandemic of 1918 [1]. Due to its high spreading rate, the virus disseminated across the world in a very short time span, forcing the World Health Organization to declare Covid-19 a global pandemic after just 3 months from the first reported case in China. At the beginning of the pandemic, when no vaccines were available, people entrust their safety to very few devices such as personal protective equipment (face masks, shields, and gloves), lock-down, and social distancing. The lack of alternative and not conventional techniques to suppress the spread of airborne epidemics among humans has pushed the research to develop new antiviral devices. The SAVE-US project (Suppression of Airborne Viral Epidemic Spread by UV-Light Barriers) aims at developing and demonstrating an innovative antimicrobial device based on 222nm-radiation. As known from the literature, the UVC radiation (200-280 nm) is the most effective wavelength for the inactivation of viruses and bacteria, corresponding to the DNA and RNA absorption peaks, but may also be mutagenic. For this reason, UVC-light sterilization is commonly performed in the absence of living organisms. Radiation in the far-UVC, especially at 222 nm, has been recently investigated because it shows a good antimicrobial efficacy, tested already on both bacteria [2] and virus [3] models including coronavirus, with very limited risks to human health. The low risk is associated to the small penetration depth of 222 nm light (a few μm): the energy is absorbed by the superficial stratum corneum of the skin that contains dead cells, with negligible irradiation of the underlying live tissue [4]. We will present the first version of a new prototype of 222 nm-illuminator and some preliminary results on its characterization;the presented device will be used in successive in vitro and in vivo experiments with SARS-CoV-2 virus. The device embeds a far-UVC lamp emitting at 222 nm, optical filters, and the controlling electronics. We show results on the spatial homogeneity of the emission intensity and the dependence on the lamp-virus distance. We also report on the ozone production due to absorption of far-UVC light from molecular oxygen naturally present in the air in order to evaluate its safety for human being and to properly evaluate its photo-killing efficacy.