The properties of hot household hygroscopic materials and their potential use for non-medical facemask decontamination

The widespread use of facemasks throughout the population is recommended by the WHO to reduce transmission of the SARS-CoV-2 virus. As some regions of the world are facing mask shortages, reuse may be necessary. However, used masks are considered as a potential hazard that may spread and transmit disease if they are not decontaminated correctly and systematically before reuse. As a result, the inappropriate decontamination practices that are commonly witnessed in the general public are challenging management of the epidemic at a large scale. To achieve public acceptance and implementation, decontamination procedures need to be low-cost and simple. We propose the use of hot hygroscopic materials to decontaminate non-medical facemasks in household settings. We report on the inactivation of a viral load on a facial mask exposed to hot hygroscopic materials for 15 minutes. As opposed to recent academic studies whereby decontamination is achieved by maintaining heat and humidity above a given value, a more flexible procedure is proposed here using a slow decaying pattern, which is both effective and easier to implement, suggesting straightforward public deployment and hence reliable implementation by the population.


Introduction
Facemasks are widely used amidst the global COVID-19 pandemic to reduce the airborne transmission in the context of social interactions (1), as high viral loads of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) might be found in asymptomatic (2) and patients positive to the disease (3). Decontamination of used facemasks is a common practice to mitigate the shortage risk (4) and the potential ecological impact of disposable units worn by billions of daily users (1). However, the recommended household decontamination procedures are time-and energyintensive (5), which can potentially lead to low public acceptance. Meanwhile, it has been shown that SARS-CoV-2 can be remaining on cloth and a surgical mask for up to seven days. The infrequent decontamination that could result can then be considered as a possible indirect vector of contamination. Quick and easy decontamination methods is therefore required. Moist heat, a combination of heat and humidity is a known treatment method of inactivating some pathogens. For example influenza viruses on stainless steel surfaces have been inactivated after being elevated during 15 minutes at the temperature of 65°C associated to a 25% relative humidity (RH) (6), while equivalent level of inactivation have been reached at 55°C and 75% RH. However, dry heat of 70°C may not be effective enough to inactivate the virus, even over a larger exposition time of an hour (7). While RH is the most reported parameter (8), absolute humidity (AH) seems to be more appropriate for predicting the influence of humidity on virus deactivation (9). During the combined heat & high absolute humidity condition, the arrangement of the lipid bilayer of the virus as well as the interactions involved in the envelope proteins could be affected (10)(11)(12). In droplets, the humidity rate and the evaporation kinetics of water can be matched (9) towards an intermediate evaporation rates and high concentration of salts, leading to virus inactivation. Therefore, aiming at benefiting from the temperature-humidity synergy, we are reporting here the SARS-CoV-2 virus inactivation from facemask in an enclosure filled with hot hygroscopic materials available in household settings.
. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted July 18, 2020. . https://doi.org/10.1101/2020.07.16.20155481 doi: medRxiv preprint

Results and discussion
The following three steps procedure is tested (Figure 1-A): Two 1L polypropylene containers, each filled with 250g of hygroscopic material, are first heated in a microwave oven for 2 minutes (i). The containers are taken out of the oven, and the mask is placed in one of them, lying on the hot hygroscopic material, while the remaining material is deposited on the mask. This step has been tested with a handling time below 1:30min (ii). The container is then hermetically sealed for 15-20 min to set a high humidity atmosphere (iii). During the first phase, the porous hygroscopic medium is exposed to micro-wave power, which results in a volumetric heat generation. Heating efficiency depends on wave interactions with polar molecules or clusters (13) described by the loss factor which is responsible for the wave attenuation and the conversion of electrical field energy into heat. In the case of dry food products, they are strongly linked to residual moisture content and starch composition (14). As a matter of fact, wheat, corn and rice starches are typically used in microwave food products formulations (15) since dielectric loss factor of these starches are commonly above 14 as compared to about 10 for water (data given at 20°C, (16)). Those materials are considered as holding potential for this decontamination method. More specifically, the process evaluated in this work is using short-cut pasta. During the decontamination of stage (iii), the mask carrying the virus is "sandwiched" between the non-consolidated hygroscopic porous media. The relative low thickness of the mask and its low heat capacity compared to the heat capacity of the porous stack (675 J K-1 for 500 g of the chosen media, compared to 30 J K-1 for a cloth mask) ensure a fast setting of a local thermal equilibrium. The evolution of mask temperature is then governed by the evolution of porous hygroscopic media temperature. As the container is sealed during this period, heat and mass transfer with the environment are reduced leading to a slow cooling process and thus maintaining a high temperature during this phase. Due to the hygroscopic nature of the chosen material (17), temperature elevation necessarily involves a vapor flux from the core of the material to its surface. This desorption rate ensures a high relative humidity in the vicinity of the mask during the entire protocol duration (Figure 1-B). For a typical case of using a 1L sealed box filled with 500 g pasta at 70°C, a desorption amount as low as 0.13 g is enough to generate a 100% relative humidity. The proposed method is thus not only able to rise the temperature of the mask to a high value (Figure 1-A), but also to develop high humidity (Figure 1-B) conditions towards virus inactivation. In the hours following of the experiment, the cooled hygroscopic porous medium will smoothly reabsorbs humidity from the environment. This can be seen as a self-reactivation mechanism which allows using the material for many further decontaminations cycles. It is expected that over the decontamination cycles, heat-induced water loss from the hygroscopic medium would reduce, leading to a higher temperature. To evaluate this effect, the inactivation tests were performed with "new" material (Test I) and material used for the 3rd time (Test II). Besides, the two tests were carried out with different heating power in different BSL3 laboratories, leading to a truly two independent validations of the decontamination process. Altogether, our results indicate that the hot hygroscopic protocol described in this work provides reliable and stable heat and humidity conditions which are efficient for inactivation of viral infectivity. This protocol holds wide potential to initiate new research in "decaying" temperature and humidity decontamination technics that are critical for the concept of frugal and reliable operation using household settings.
. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

Materials and Methods
For each inactivation study, 15 000 VERO E6 cells were seeded in 24 well plates for 24 hours to reach 80% confluence. A 25 µl sample of viral solution (5.13 Log TCID50/ml for test I and 4.84 Log TCID50/ml for test II) was spotted on paper patches such as antibiotic disks. Three infections were carried on in parallel (samples 1, 2 and 3) for each mask. Paper disks spotted with 25 µl of viral solution, either treated with hygroscopic materials or untreated, were used as negative control. A positive control corresponding to the spotted but untreated virus was also performed. Patches containing the virus were settled in a whole mask folds (to mimic real conditions of decontamination of an entire mask). The mask was then subject to the above described decontamination procedure. After 20 minutes for test I and 15 minutes for test II, the patches were recovered and incubated in cell culture medium for another 15 minutes, and the eluates were used to infect VERO cells. The cells were observed at 2 days, 5, 6, 7 days and 9 days (not shown) post-infection to follow the appearance of cytopathic effect. While cells with untreated virus (Fig. 2, positive control) were lysed, cells incubated with treated virus continued growing and did not show any cytopathic effect even 9 days post infection, showing the efficacy of the treatment. No toxic product was released after treatment with hygroscopic materials (negative treated control). RNA from inactivation test II were also extracted and amplified by qRT-PCR. Three regions of SARS CoV 2 genome were targeted (N, and two regions of Orf 1ab). While the viral RNA was detected in positive sample as expected (Ct around 15,9)), samples treated with the hygroscopic process were undetected as for the negative control and for the three amplified regions, which correspond to a loss of infectivity above 5 log.  Fig. 2. (B) Temperature, Water loss, and Water vapor desorption rate from initial 500g of hygroscopic material during and after a household-compatible heat and humidity decontamination process. The desorption rate is linked to the concentration of water at the surface of the medium, and thus, its pattern is a direct image of the material temperature. The fast heating process does not lead the hygroscopic medium to release all the water it contains, because the mass loss is limited by the slow material water mobility . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted July 18, 2020. . https://doi.org/10.1101/2020.07.16.20155481 doi: medRxiv preprint