Integrated photothermal decontamination device for N95 respirators -Integrated photothermal decontamination device for N95 respirators International Burch University
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Integrated photothermal decontamination device for N95 respirators



Since the end of 2019 and throughout of 2020, the world has been facing a global pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Globally, over 25 million confirmed cases have been reported, with over 800,000 deaths, numbers which are expected to increase.

One of the many concerns and challenges that many countries have faced is the shortage in Personal Protective Equipment (PPE) for frontline healthcare workers. The fluidity of the pandemic progression will most likely extend the PPE shortage to other regions in the globe. This shortage of PPE puts at risk both healthcare professionals and patients. One of the PPE that has been in high demand since the beginning of the outbreak are N95 respirators. These respirators, or masks, help reducing the spread of the virus and protect frontline workers that are treating COVID-19 patients. Even though N95 respirators are intended for single-use; the exponential consumption of N95 masks has brought the need for finding effective and safe decontamination protocols that can increase the number of uses of the respirators, without damaging the physical integrity and filtering properties.

Bacteria and viruses can be deactivated using UV irradiation, with several studies reported using UVC for decontamination. This deactivation takes place via the production of free radicals that are formed upon the direct interaction of light with the organism’s biomolecules, mainly DNA. However, some species have demonstrated to be resistant to UV and could remain active even after irradiation. Thus, thermal deactivation has been widely use as alternative for eradicating viruses and bacteria.

The primary advantage of using methods such as UV-C and/or heat (in conjunction or alone), when compared to other methods, is that operational personnel can be easily trained, deployed, and specialized facilities are not required for its application.

N95 Photothermal decontamination device.
(A) Decontamination cycle. Te masks are labeled, located in the mask holders and center shaf, placed inside of the device, exposed to UV light followed by heat exposure. WC=White Cycle is when UV is used for 7 min, CC=Color Cycle is when UV is used for 10.5 min. (B) Photoreactor LZC 4, Luzchem Research Inc., originally used to irradiate up to 4 masks in a semi-manual cycle. (C) initial heat application device in prewarmed oven at 60 °C used to treated up to 4 masks per cycle. (D) A commercial device designed and manufactured by Luzchem Research Inc, in operation. (E) Te assembly of the mask holders and location of masks is safely done using a 3D printed shaf support outside of the device to prevent UV exposure and contact with high-temperature surfaces. (F) 3D printed mask stand holder, that allows easily loading of the masks into the shaf.

Decontamination device. It has been reported that the use of UV-C light and high temperature can effectively eliminate coronaviruses. However, most of these protocols and devices make use of either UV-C or heat alone. Since the fine balance between virus eradication and bacteria killing is critical for safely reusing N95 respirators; we set out for developing a technology that combines both temperature and UV irradiation. The initial prototyping involved the use of separated irradiation and temperature devices. This non-automatized decontamination process was able to only load 4 masks per cycle in bench size instruments.

Further, since the mask holders remained static, we had to add a step where the irradiation was turned of and the masks positions exchanged to minimize the “shadowed” areas. Apart from the non-homogenous irradiation, we also identified a potential risk of cross contamination when the respirators were transferred between devices. Also, reducing potential risks to the operator, such as UV exposure, as well with a much larger loading capabilities, led to the development of a fully automatized Photothermal Decontamination Device (LPD) by Luzchem Research Inc.

The LPD system is able to decontaminate up to 20 masks under 30 min. The decontamination process uses a proprietary combination of UV-C and UV-B irradiation (2.2 J/cm2 ), which maximizes light penetration within the N95 respirators. Further, LPD incorporates irradiation protocols with different time lengths specifically designed for colored N95 respirators. Immediately after the irradiation cycles are completed, a temperature treatment (60 °C) for 12 min is used. The short irradiation times used in the LPD system allows for up to 18 months of lifetime of the UV lamps (calculated on 8-h non-stop cycles), which is equivalent to+300 N95 respirators decontaminated per day.

Mask holders and center shaft support design. Once 3D printed, the mask holders can be safely attached on each support shaf using an easy-to-assemble, 3D printed assembling system. This system allows for the assembly of two vertically aligned mask holders per support shaf, thus effectively utilizing the space within the device to decontaminate more masks per cycle. Te center shaf can be easily removed from the device using a push-button system, such that the loading and unloading of the masks can be done outside of the device, reducing the risk of UV light exposure or the contact with high-temperature surfaces by the operator. Multiple center-shafs were designed for each device, such that the decontamination process was made timeefficient, and the operator could load a set of masks, while another set was being decontaminated. To ease the loading and unloading of the masks, a support for the center shaf was designed and 3D printed using polylactic acid (PLA) flament. The center shaf can be safely located on the support and the user can assemble and load the masks.

Validation of decontamination cycles. The impact of the photothermal decontamination on the filtering capacity, ft of the masks, filtration efficiency, physical integrity, microbial, and virus survival were also examined.

Physical inspection. In this study, we tested different types of masks available in our Health Care Center. For the purposes of our study the masks selected were classified in the categories. First, the physical integrity of the masks (visual inspection for physical damage, integrity of the elastic bands, and odor inspection) was evaluated after each decontamination cycle. A scoring system from 0 (not useful) to 3 (no changes) was assigned to each parameter by a blind independent individual. From the physical inspection, all the masks showed acceptable physical evaluation for over 3 decontamination cycles.

Fit testing and filtration capacity. Assessing the filtration capabilities of the mask after each decontamination cycle is critical to demonstrate the ability of the mask to filter sub-micron particles and to mimic real conditions of mask use. The N95 respirators are characterized for particle filtration>95%. To evaluate the filtration capabilities of the mask after each cycle, five models of N95 masks were ft tested for up to 3 decontamination cycles. An overall fitting score above 100 is equivalent to superior filtration capacity of the mask. In all cases, fitting scores were above 100. Furthermore, filtration of 0.075 μm particles were measured and it was observed that all masks filtered>99% of the particles after 3 decontamination cycles.

Structural integrity. To evaluate the structural integrity of the masks after each decontamination cycle, Optical Coherence Tomography (OCT) analyses were carried out. This non-destructive technique allows for a 10 μm resolution or less into the penetration layers. A light source of 820nm from the OCT allowed for the imaging of the first layers of the N95 masks after each cycle. In addition, for comparison purposes, some masks were cleaned in a wet autoclave cycle and imaged after one autoclave cycle. Two models of N95 masks (1860S and 8210) were subjected to 3 cycles of photothermal decontamination (1860S used Color Cycle, and 8210 used White Cycle) or to one cycle of autoclaving.

Microbiological decontamination validation.

Bacterial decontamination. To assess the ability of the device to decontaminate N95 masks, 3 bacterial strains were used: Staphylococcus Epidermidis (S. Epidermidis), Pseudomona Aeruginosa (P. Aeruginosa), and Geobacillus Stearothermophilus (G. Stearothermophilus). G. Stearothermophilus is a standard bacterial strain used for validation of wet sterilization cycles. Its capabilities as a bacteria thermophila (it is able to growth at 55 °C)35 make it an ideal strain to determine the efficacy of our device to effectively decontaminate PPE. Furthermore, a qualitative biological test was evaluated with spore strips of the strain Bacillus Pumilus, which is a reference standard microorganism test for high radiation devices. We selected three mask models: 1860, 8210, and 1870+. Each mask was inoculated with a bacterial concentration of ≈1010 CFU/mL. This concentration value exceeds the standard used to certify face masks in the industry (5×105  CFU/mL, ASTM F2101)39. The bacteria were spread homogenously on the surface and let absorbed into the inner layers of the mask for 1-h prior to testing. The inoculated samples with and without the decontamination cycles were transferred to plates containing sterile bacteria culture media and incubated for 1 h. Then, 10 µl of that solution was plated for counting analysis.

Viral decontamination. The effects of the decontamination process on viral infection were then investigated by testing the infectious ability of the Lentivirus on HEK293A cells upon UV and UV+heat treatments. As a surrogate virus model for SARS-CoV-2, we used a Lentivirus bearing a green fuorescent protein (GFP) reporter. It has been known that the spikes of different coronaviruses can be pseudotyped in order to create safer experimental models. Previous studies showed that HIV-based Lentiviral particles were used as a model in numerous SARS-CoV-2 studies. The surface glycoproteins of coronaviruses play an important role in receptor binding and cell entry. This makes Lentivirus a good candidate for our study as they share similar envelope and lipid bilayer surface features. Our results showed that, similar to the bacteria tests, decontamination cycles resulted in a significant reduction in viral infection.

The LPD device combines UV-B and C and a short mild temperature to effectively decontaminate up to 20 masks at a time in less than 30 min. The decontaminated N95 respirators showed no physical damage after 3 cycles, with no significant signs of degradation of the filtering materials or elastic bands. From the ft testing, it was determined that the mask models could undergo up to 3 cycles of decontamination. Additionally, the layer thickness and material density of the masks afer decontamination with our device was not impacted afer multiple cycles. Exploratory tests increasing the number of decontaminations cycle up to 50 cycles showed that respirators are still suitable for use, although there was a wearing of the elastic bands. Furthermore, our device was able to eliminate 8 log10 of P. Aeruginosa, S. epidermidis, and G. Stearothermophilus and 4 log10 of our surrogate Lentivirus from within the different mask layers. Overall, the photothermal decontamination device presented here is an attractive and cost-effective tool with a relatively small footprint that allows for a solvent/gas free, and dry decontamination of N95 masks without compromising their macro and microscopic physical integrity and filtering capacity. Further development of N95 respirators could incorporate using activatable materials that absorb in the visible spectrum for allowing for “real-time” sunlight bacterial and viral eradication.


Department of Genetics and Bioengineering