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Virus dies most at intermediate humidity

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Rome, 23 April (beraking latest news Health) – Sars-Cov-2 survives for less time on more hydrophilic surfaces such as glass than less hydrophilic ones, such as some plastics. And its longer permanence depends on two key factors: climatic conditions such as air temperature and humidity, and the surface properties of the materials. Viruses in particular struggle to survive in intermediate humidity, while they proliferate at very low or high humidity and with increasing temperatures. This is what emerges from a study, conducted by the University of Trento and Federico II of Naples, published in ‘Frontiers in Materials’, which responded to the many doubts circulated since the beginning of the Covid-19 pandemic on the fact that, besides hands, it is necessary to repeatedly sanitize many objects of daily use, starting from smartphones, keyboards, desks, shoes and clothes, as well as public transport.

The researchers therefore made calculations to understand how long the coronavirus could survive on different surfaces, also with a view to designing them so that one day they will be virus-proof. The study detects the survival of viruses on surfaces and highlights how the permanence depends on the environmental conditions and the type of material. For example, viruses struggle to survive in intermediate humidity, while they proliferate at very low or high humidity and as temperatures rise.

Not only. The research also lays the foundation for understanding the link between survival and wettability (the ability of a liquid to wet a solid) of a surface by a drop of saliva. In particular, a shorter survival time is expected on glass and longer on some plastics.

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The microscopic drops of saliva that are dispersed in speaking, coughing and sneezing remain partly suspended in the air and partly settle on surfaces, depending on their size. “Various viruses, including coronaviruses, can survive several hours or even days in the drops deposited”, say the authors of the study, conducted by Nicolò Di Novo under the supervision of Nicola Pugno of the University of Trento, in collaboration with Massimiliano Fraldi, Giuseppe Mensitieri and Angelo Rosario Carotenuto of the Federico II University of Naples.

“The virological experiments have shown that the temperature and humidity of the air and the surface properties of the materials – they explain – influence the persistence and contagious potential of the viruses contained in the drops. In particular, the survival of some viruses has a trend called shape of ‘U’ with respect to relative humidity, with a peak of “virus” mortality at intermediate humidity, while it increases with increasing temperature. In fact, environmental conditions determine the chemical-physical history of a drop of saliva, conditioning its process In fact, since saliva is a complex liquid, in which various non-volatile substances such as salts, biomolecules and proteins are present, the process of evaporation of the water of which the drop is composed modifies the concentration of these substances and the level of acidity of the microenvironment of the virus, jeopardizing its activity or instead prolonging its vitality “.

“From the study – the authors conclude – therefore, a clear description emerges for the first time of the mechanism that leads to a higher mortality of viruses with intermediate humidity, the prediction of the survival time of some viruses similar to coronaviruses, and some formulas are also provided mathematics that allow to link the survival of the virus in the droplets of saliva that are deposited on the surfaces with the wettability of the same through a parameter that characterizes the different materials, called the ‘contact angle’. In particular, these results suggest a shorter survival time on more hydrophilic surfaces such as glass compared to less hydrophilic ones such as some plastics, confirming some experiments reported in the scientific literature “.

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