{"paper_id":"11dcf7b7-e875-4088-8949-b623bfdeb83b","body_text":"Specificity of UV-C LED Disinfection Efficacy for Three N95 Respirators | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Specificity of UV-C LED Disinfection Efficacy for Three N95 Respirators C. Carolina Ontiveros, David C. Shoults, Sean MacIsaac, Kyle D. Rauch, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-435322/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Jul, 2021 Read the published version in Scientific Reports → Version 1 posted 9 You are reading this latest preprint version Abstract The recent surge in the use of UV technology for personal protective equipment (PPE) has created a unique learning opportunity for the UV industry to deepen surface disinfection knowledge, especially on surfaces with complex geometries, such as the N95 filter facepiece respirators (FFR). The work outlined in this study addresses the interconnectedness of independent variables (e.g., UV Fluence, respirator material) that require consideration when assessing UV light efficacy for disinfecting respirators. Through electron microscopy and Fourier-transform infrared (FTIR) spectroscopy, we characterized respirator filter layers and revealed that polymer type affects disinfection efficacy. Specifically, FFR layers made from polypropylene (PP) (hydrophobic in nature) resulted in higher disinfection efficiency than layers composed of polyethylene terephthalate (PET-P) (hygroscopic in nature). An analysis of elastic band materials on the respirators indicated that silicone rubber-based bands achieved higher disinfection efficiency than PET-P bands and have a woven, fabric-like texture. While there is a strong desire to repurpose respirators, through this work we demonstrated that the design of an appropriate UV system is essential and that only respirators meeting specific design criteria may be reasonable for repurposing via UV disinfection. Materials Engineering General Microbiology Photonics/optics personal protective equipment (PPE) N95 filter facepiece respirators (FFR) Fourier-transform infrared (FTIR PET-P bands Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction There has been acute shortages of single-use N95 filter facepiece respirators (FFR) during the COVID-19 pandemic 1 . Consequently, an urgent call was made for suitable disinfection technologies for FFR reuse in response to shortages to overcome the critical need for PPE to ensure healthcare staff safety 2 . Some healthcare jurisdictions resorted to improvised FFR recycling programs where entire rooms were designated as spaces to expose used FFR to ultraviolet (UV) light to disinfect them for reuse 3 . The efficacy and suitability of several disinfection technologies have been investigated in recent years, including autoclaving, ethylene oxide (EtO), vaporized hydrogen peroxide (VHP), bleach, microwave irradiation, and UV irradiation 4 , 5 . This study concluded that FFR disinfection by microwave oven and bleach were the least desirable due to melting of the respirator material and lingering smells of bleach, respectively. Additionally, UV irradiation is considered the most promising of the five disinfection approaches investigated by) due to throughput advantages over EtO and VHP 5 . UV irradiation has been used in drinking water and wastewater treatment for decades, and more recently, has been shown to be effective for surface disinfection in food processing 6 – 8 and on other surfaces 9 , 10 . UV disinfection has several advantages over other disinfection methods due to its generally low environmental impacts, ease of use, and relatively small space requirements 11 . The suitability of UV disinfection as a germicidal process for more intricate materials (such as FFRs) is less understood. One of the limitations of UV treatment technologies is its ineffectiveness when light-shielding materials are present. UV shielding is particularly important when considering FFRs, as their surface geometry is complex and may lead to shaded areas that are not exposed to UV light. FFR geometry and material properties are hypothesized to play a role in shielding organisms from UV, resulting in reduced efficacy 5 . Thus, there is a knowledge gap in understanding the interactions between UV light and complex surfaces and a need for further investigation to harness UV disinfection technologies for decontaminating FFR materials. Before the COVID-19 pandemic, data on UV disinfection of FFR was limited 12 . Previously conducted studies examining UV irradiation on FFRs are not current, contained methods that were difficult to compare with other studies, and required an update to fit the needs of the COVID-19 pandemic 5,13−15 . Supply chain interruptions for personal protective equipment (PPE) led some jurisdictions to authorize emergency reuse of FFRs and other PPE, which resulted in an increase in studies investigating the efficacy of UV disinfection of these materials 2 , 12 , 16 , 17 . A recent surge of surface-UV exposure products brought to market for disinfecting FFRs, personal objects, and surfaces have resulted in additional measures by the U.S. Food and Drug Administration (FDA) to ensure consumer safety 18 , 19 . However, the guidelines provided by the FDA and the National Institute of Standards and Technology (NIST) are in their preliminary stage, and there is a lack of guidance towards best practices for validating FFR disinfection processes. The design of UV disinfection studies for FFRs requires careful consideration of several variables that may impact results. For example, the FFR model used, material layers selected for inoculation, and microorganism loading density must be considered. Further, in light of the public health significance of N95 respirators, disinfection studies must be carefully designed to minimize the number of respirators needed for research purposes. Accordingly, we designed an efficient experimental study with the aim of understanding the impact of multiple parameters on FFR material disinfection using UV irradiation. Experimental factors studied included UV fluence, test organism, inoculation concentration, inter-layer inoculation, and strap material. We also addressed the impact that FFR model type has on disinfection efficiency, which to date has not been sufficiently addressed in current literature. 2. Methods 2.1 Microbiological propagation and enumeration All experiments were conducted with Pseudomonas aeruginosa PA01 and MS2 bacteriophage (ATCC 15597-B1) as performance surrogates for bacteria and viruses, respectively. For bacterial testing, tryptic soy broth (TSB) was inoculated with 100 µL of overnight culture to create a 4-h subculture. P. aeruginosa was enumerated using both the spread plate and membrane filtration methods on cetrimide agar, according to Standard Methods (D5465–16) 20 . Membrane filtration assays were performed using the entirety of sample solutions after volumes were removed for spread plating assays (~ 17.7 mL). MS2 was propagated and enumerated using the double-layer agar method on tryptic soy agar (TSA) with Escherichia coli 3000 (ATCC 15597) as a host, according to Method 1601 21 . Both P. aeruginosa and MS2 agar plate assays were incubated for 18–24 h at 37°C. 2.2 FFR coupon inoculation, exposure, and recovery Coupons were made from 1-cm diameter material from 9210 and 8110s or 8210 (equivalents) N95 FFRs (3M, USA). N95 FFR strap coupons (1 cm 2 ) were cut from 1860 and 8110s/8210 N95 FFRs (3M, USA). Before inoculation, P. aeruginosa or MS2 working stocks were diluted into either phosphate buffer solution (PBS) or TSB to the desired concentration. In the single case when an extremely high P. aeruginosa concentration was required, the working stock was centrifuged at 3,000 RPM for 10 min and resuspended in TSB. Depending on the experiment, duplicate or triplicate respirator material coupons or strap sections were placed inside sterile 47-mm Petri dishes and inoculated with the diluted P. aeruginosa or MS2 by pipetting 5-µL droplets onto the surface of the coupon. Droplets were then spread with a cooled flame-sterilized glass spreader and allowed to dry for 20 min. The estimated loadings are reported as colony-forming units (CFU) or plaque-forming units (PFU) per cm 2 (Table 1 ). Petri dishes containing inoculated coupon samples were placed 1.5 cm beneath the collimator onto a 30 RPM rotating platform with the inoculated surface facing up to ensure uniform UV exposure. Following exposure, each FFR coupon was placed in a sterile 50-mL conical tube containing 20 mL sterile PBS using flame-sterilized tweezers. Each strap coupon was placed in a sterile 2-mL dilution tube containing 0.9 mL sterile PBS. For both sample types, tubes containing samples were vortexed at 3000 RPM for 1 min to facilitate the shedding of microorganisms. The resulting liquid suspension from each sample, referred to as sample solution, was then used for serial dilutions or plated directly from the sample solution. For both spread plating and the double-layer agar method, serially diluted 100-µL samples were plated. In cases where high inactivation levels were anticipated, 1 mL of undiluted MS2 and P. aeruginosa sample solutions were plated. Additionally, P. aeruginosa sample solutions were used for membrane filtration plating of P. aeruginosa . For each variable parameter ( i.e ., concentration, respirator material), positive controls (no UV exposure) were prepared for comparison with treated samples for log reduction value (LRV) estimation. Positive control recovery was carried out as described above, absent UV exposure. 2.3 UV collimated beam apparatus UV inactivation experiments were conducted using the 280 nm wavelength on a UV-C LED collimated beam apparatus (PearlLab Beam T 255/280/365, Aquisense, USA). Irradiance was measured using a USB4000 Ocean Optics spectroradiometer (Ocean Optics, USA). Irradiance measurements were collected with 0.5-mm spatial resolution across the face of the coupons and were used to calculate the Petri Factor (0.890). The average irradiance delivered to FFR coupons was determined using the product of a central irradiance measurement and the Petri Factor and was calculated to be 794 µW cm − 2 . The desired fluence was divided by the average irradiance to determine the required exposure time. 2.4 Intra-Layer Inoculation N95 respirators are composed of multiple layers. The 9210 FFR (Fig. 1 b) is composed of an outer hydrophobic layer (L1), a middle electrostatically charged layer (L2), and an inner biocompatible layer (L3), as described by a previous study 17 . L3 was dissected into three sub-layers (a, b, & c) to investigate the nature of the respirator material further. The hydrophobic nature of N95 respirator material is intended to repel 95% of aerosolized droplets; however, droplet nuclei may penetrate the outer hydrophobic layer and become trapped in the electrostatic layers of the material. An inter-layer study was conducted using coupons cut from the N95-9210 FFR model to investigate differences in the reduction of organisms that may be present within FFR layers. Eight combinations of inter-layer inoculation and UV-C exposure direction were investigated. Figure 1 illustrates the layer configuration and labelling scheme. All arrangements were exposed to 500 mJ cm − 2 of UV-C 280 nm. Coupon layers were peeled back using flame-sterilized tweezers and inoculated as described in Sect. 2.4. Figure 2 illustrates the eight combinations of inter-layer inoculation location and exposure direction. 2.5 Respirator layer analysis Material characterization was conducted on different respirator models to analyze the different respirator layers and their role in disinfection efficacy. Layers and straps of N95 respirator models 9205, 9210, 8210, 1804, and 1860 were characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Samples of FFR layers and straps from each of the models were treated with gold sputtering and then scanned at 302 and 55x magnification. FTIR measures the infrared absorption and emission spectra of the sample and infers the functional groups present. An FTIR (Bruker Alpha, USA) equipped with the solid-phase attachment was used for all samples. For FTIR analysis, only N95 1860, 8210 and 9210 models are presented in Fig. 6 . Material characterization information for additional respirator models can be found in Supplementary Figure S2. FTIR samples were prepared by cutting a 1-cm 2 coupon from each respirator layer and placing them beneath the FTIR instrument head. Sample spectra were matched with profiles from the Bruker library to identify the most probable material type. Spectra were then exported as CSV files for further data management using the R programming environment. Results can be found in Supplementary Figure S3. 2.6 Irradiance through 9210 FFR layers UV light penetration through the N95 9210 respirator layers was tested using the UV-C LED collimated beam apparatus (PearlLab Beam T 255/280/365, Aquisense, USA). The UV light was measured using a USB4000 spectrometer (Ocean Optics Inc., USA) to determine the proportion of UV light blocked by the layers of the 9210 respirators. Light penetration was assessed by clipping combinations of coupons of 9210 respirator layers to the surface of a spectroradiometer detector as described in a previous study 17 . 2.7 Replicates, limits of detection and quantification, statistics, and data visualization For each experiment, a minimum of two biological replicates ( i.e. , two coupons) was performed for each combination of variables ( i.e. , fluence, respirator layer). Each biological replicate was enumerated via two technical replicates ( i.e. , two assays) across a minimum of three 10-fold dilutions for spread-plating ( P. aeruginosa ) and the double-layer agar (MS2) assays. A single membrane filtration assay was performed for each biological replicate of treated P. aeruginosa samples. Positive controls were processed for each experiment, including separate sets of controls when different materials, layers, or concentrations were investigated. All data were analyzed and visualized using R v4.0.0 and RStudio v1.1.463 22 using the Tidyverse 23 , Ggplot2 24 , Dplyr 25 , Ggsci 26 and RColorBrewer 27 packages. For both P. aeruginosa and MS2, non-detects (ND) were < 1 CFU/PFU per maximum volume plated. Where appropriate, paired t-tests were conducted at a significance level of α = 0.05. When comparing UV fluences, one-sided t-tests were performed. In all other cases, two-sided t-tests were performed. 2.8 Experimental design A fluence of 50 mJ cm − 2 was used to test the UV-C efficacy of four P. aeruginosa loading concentrations. Preliminary experimentation (data not shown) suggested that in some instances, 100 mJ cm − 2 was sufficient to reduce P. aeruginosa to below detection; therefore, a fluence of 50 mJ cm − 2 was chosen to measure disparities in LRVs between different loading concentrations. The loading concentrations are described in Table 1 . UV-C (280 nm) light blockage was investigated using various layer combinations for both the 9210 and 8110s N95 models. Respirator layers were fastened on top of the spectrometer, then placed below the collimated beam. Thirty irradiation readings were taken per layer combination and averaged. These values were then compared to the averaged readings taken when no layers were present between the UV-C light source and spectrometer to estimate the percentage of 280 nm light blocked by each layer or layer combination. For clarity, a summary of all experiments is detailed in Table 1 , which includes the objective, test-organism, layer-exposure arrangement (see Fig. 2 ), fluences, coupon/elastic material, biological replicates, and microorganism loading. Table 1 Experimental summary of organism, inoculation concentration, FFR material, exposure arrangement, fluences, and replicates Objective Organism Inoculation concentration (CFU/PFU cm − 2 ) FFR Material Layer-exposure arrangement (Fig. 2 ) UV-C fluences (mJ cm − 2 ) Biological replicates Fluence response (coupon) MS2 6.9E + 08 9210 1 & 8 0, 50, 100, 500, 700, 1000 2 per fluence per arrangement MS2 6.9E + 08 8110s/8210 1 & 8 0, 100, 500, 1000 2 per fluence per arrangement P. aeruginosa 3.9E + 06 9210 1 0, 100, 500, 1000 3 per fluence Fluence response (straps) MS2 6.9E + 08 9210 (rubber) Direct 0, 50, 100, 500, 700, 1000 2 per fluence 1860 (polyester) Direct 0, 50, 100, 500, 700, 1000, 1400* 2 per fluence Bacterial loading (coupon) P. aeruginosa 4.0E + 03 4.0E + 04 3.2E + 05 1.6E + 06 9210 1 0 and 50 3 per fluence per concentration 1.6E + 06 5.0E + 07 9210 1 0 and 1000 3 per fluence per concentration Inter-layer inoculation MS2 6.9E + 08 9210 1–8 0 and 500 2 per fluence per arrangement *The polyester elastic absorbed the inoculation liquid; therefore, the elastic was flipped over after 700 mJ cm − 2 to expose both sides. 2.9 Control experiments Since it is not common to combine spread plating and membrane filtration for enumeration comparison, as they may vary in accuracy and precision, a recovery experiment was performed to determine if there was a significant difference in recovery efficiency between the two methods. To do so, P. aeruginosa was assayed via both enumeration techniques with 12 replicates for both. The results of these experiments can be found in SI 1. 3. Results And Discussion 3.1 Effects of respirator material and UV-C fluence Coupons from two 3M N95 respirator models (8110s & 9210) were inoculated with MS2 and exposed to an array of UV-C 280 nm fluences ranging from 50 to 1,000 mJ cm − 2 to examine the relative effects of fluence and type of respirator material. The results of this experiment are shown in Fig. 3 . FFR model 9210 At 50, 100, and 500 mJ cm − 2 (Fig. 3 ), MS2 LRVs observed for the 9210 FFR differed significantly between L1 and L3 ( p = 0.0009, 0.01, & 0.01, respectively). At fluences of 700 and 1,000 mJ cm − 2 , no significant difference in MS2 reduction was observed between L1 and L3 ( p = 0.9 & 0.07, respectively). This difference suggests that the outer-most layer (L1) requires a higher UV-C fluence for inactivation. For L1, MS2 LRV increases between fluences were significant up until 500 mJ cm − 2 , after which no significant differences were observed. For L3, LRV increases were significant between 50 and 100 mJ cm − 2 ( p = 0.02), after which no significant increases in LRV were observed. In Supplementary Figure S1, P. aeruginosa LRVs observed for 9210-L1 were similar to that observed with MS2. The similarity in kinetics between MS2 and P. aeruginosa was surprising, given that MS2 typically requires UV fluences which are orders of magnitude higher than what is required for a similar LRV of P. aeruginosa 28 , 29 . Supplementary Figure S1 illustrates an observable difference in P. aeruginosa LRVs between 100 and 500 mJ cm − 2 . Between 500 and 1,000 mJ cm − 2 , the LRVs were virtually the same, both having two treated samples with non-detectable levels of P. aeruginosa . FFR model 8110s/8210 A significant difference in LRV was observed between L1 and L3 of the 8110s FFR at 500 mJ cm − 2 ( p = 0.02) but not at 100 and 1,000 mJ cm − 2 ( p = 0.3 for both fluences). Further, there was no significant increase in LRV at fluences after 100 mJ cm − 2 ( p > 0.05). The most drastic LRV differences were observed between the 9210 and 8110s respirator models. Significant differences ( p < < 0.05) were observed between both respirator models for both arrangements and all paired fluences (100, 500, & 1,000 mJ cm − 2 ). The disparities in LRV observed between the two respirator models are consistent with previous studies 5 , 30 , who found that the effectiveness of various decontamination methods was model-dependent, given their differences in design, materials, and hydrophobicity. However, a more recent study 31 did not find a statistical difference between hydrophobic versus hydrophilic respirator materials. In summary, the outer-most layer (L1) of the 9210 FFR requires higher UV-C fluences than the inner-most layer (L3) to reach the maximum observed MS2 LRV of just over 5. Additionally, UV is considerably more effective for inactivating MS2 on 9210 FFRs relative to 8110s FFRs and higher than 5 LRVs on MS2 are achievable at UV-C 280 nm fluences of 100 and 500 mJ cm − 2 for L3 and L1 of the 9210 FFR, respectively. As shown in Fig. 3 , both respirator models and the inoculation/exposure arrangement considerably affected UV efficacy. Although both FFR models are comparable in terms of certification by The National Institute for Occupational Safety and Health (NIOSH), they responded differently in terms of UV disinfection. LRVs above 1.5 were not observed with the 8110s/8210 FFR model, even at fluences of 1,000 mJ cm − 2 . The 9210 FFR model resulted in a more pronounced disinfection curve, where LRVs between 5 and 6 were observed for both L1 and L3 starting at doses of 500 and 100 mJ cm − 2 , respectively. Proposed stringent regulations of 3 and 6 LRVs 32 for Tier 3 and Tier 2 certification, respectively; however, these results suggest that UV disinfection technologies may behold specificity for FFR models, which is not contemplated in regulatory constructs. Future UV validation studies for FFR disinfection should place emphasis on the model of FFR investigated to understand disinfection efficacy and specificity further. 3.2 FFR elastic material and UV-C fluence Strap segments from two FFR models were inoculated with MS2 and exposed to UV-C irradiation at fluences of 280-nm. The objectives were to i) understand the UV-C kinetics for MS2 on FFR straps and ii) determine if strap material plays a role in UV efficacy for treating FFR straps. Rubber-elastic (9210) and polyester-elastic (1860) straps were tested. The LRVs observed with the rubber elastic from the 9210 FFR increased steadily until 500 mJ cm − 2 , where all samples were reduced to either below the LOQ or below detection. However, the LRVs observed with the polyester elastic from the 1860 FFR were considerably less. LRVs remained at or below 0.5 for fluences of 50 to 1,000 mJ cm − 2 . When each side of the elastic was exposed to 700 mJ cm − 2 for a total of 1,400 mJ cm − 2 , LRVs were higher than when one side was exposed to 1,000 mJ cm − 2 ; however, the difference was relatively small (0.17, p = 0.003). Figure 5 shows that similarly to the 9210-respirator material, MS2 LRVs > 5 are observed at a fluence of 500 mJ cm − 2 for 9210 rubber-elastic straps. When treating the polyester-elastic 1860 respirator straps, it was impossible to achieve more than one LRV, even when exposed to UV-C fluences higher than 1,000 mJ cm − 2 , which are generally sufficient under other conditions. Additionally, even when the 1860 polyester straps were exposed to UV-C fluences (700 mJ cm − 2 per side), LRVs were not substantially increased. SEM results (Fig. 6 ) show that the polyester strap is much more intricate at a microscopic level than the rubber strap from other FFR models. This intricate geometry is likely absorbing the inoculum and preventing UV-C radiation from penetrating the strap material, in contrast with rubber straps where the inoculum droplets stay on top of the material. Including strap material in disinfection experiments is critical to determine if specific N95 FFRs models will be suitable candidates for a given disinfection strategy. The results presented in Fig. 5 show that the 1860 FFR model and any other model with polyester nature straps may not be suitable for UV-C disinfection, at least below an applied fluence of 1,400 mJ cm − 2 . 3.3 Effects of bacterial loading The relative effects of microbial concentrations on disinfection performance are not well understood, especially concerning FFR materials. For this reason, we investigated the relative effects of P. aeruginosa cell-density inoculated onto 9210 FFR coupons on LRVs (Fig. 6 ). P. aeruginosa was recovered at similar concentrations in treated samples ( p < 0.05 for all comparisons) across all cell-densities examined, resulting in an increased LRV as cell-densities increased (Fig. 6 ). Increased cell-densities that would result in more significant shielding were expected but were not observed in this result. The data in this study suggest that if cell-densities are too low, there is a diminishing return in efficacy with respect to LRVs. The implications of these results are essential for the design of standardized performance-testing protocols. Furthermore, a more direct comparison between studies would be possible if cell-densities were reported. For example, a recent study 31 achieved > 5 LRV with MS2, whereas other studies 13 ,33 only achieved around 3 LRV with MS2 as well. None of these studies mentioned cell density; additionally, inoculation medium, FFR model used, and inoculation technique was also different. These disparity among studies may be impacted by cell-densities or other factors that were different, such as respirator type and inoculation location, as shown in Fig. 3 . A second experiment was conducted to address potential differences at higher cell-densities and a higher UV-C 280-nm fluence. As shown in Fig. 5 , there may exist a critical cell-density threshold somewhere between 6.2 and 7.7 log CFU cm − 2 , in which cell-densities exceeding such a threshold result in over-aggregation of bacterial cells, leading to reduced LRVs. 3.4 Materials characterization of three N95 FFR models Figure 6 summarizes the material characterization of the 1860, 8210 and 9210 N95 respirators. Only the three primary and more easily separated layers were analyzed. Layer nomenclature is as depicted in Fig. 1 A. The main polymers found in the layers of the respirator were Polypropylene (PP), Polyethylene Terephthalate (PET-P), Polydimethylsiloxane (PDMS), and Eltec P HP-603 Polypropylene. PP is considered a thermoplastic polymer used in a wide range of applications. PP presents non-polar properties, which indicates a low interaction with water 34 . In contrast, PET is a polar plastic, commonly found in plastic bottles 35 . PET has an intrinsic viscosity and hygroscopic nature (retains water from its surroundings). Moreover, PDMS is a commercially-available silicon rubber 36 that is viscoelastic and hydrophobic (repels water). The 1860 model layers were mainly comprised of PP (L1 and L2) and PET (L3), while the straps were composed of PET. Comparatively, the 9210 model mainly had PP (L1, L2 and L3) and PDMS (rubber) for the straps, while the 8210 model primarily consisted of PET (L1 and L3), Eltec P HP-603 Polypropylene (L2), and Bunatex K 71 (straps). The respirator materials and their configuration within the layers of the respirators could explain the difference in disinfection found in the respirator microbial testing. Figure 3 and Fig. 4 show that the 9210 respirator achieved higher LRVs in both MS2 and P. aeruginosa tests. The 9210 and 1860 respirator models have a more plastic feel on L1 than the 8210 model, which has a softer and more fabric-like texture. The 1860 respirator straps, which have a fabric-like texture, resulted in low LRVs compared to the 9210 model, even when applying 700 mJ cm − 2 per side. The low LRV value achieved on the 1860 strap may be attributed to the hygroscopic nature of PET, contrary to the 9210-respirator strap, which is mainly composed of hydrophobic PDMS. The higher disinfection efficiency on the 9210 respirator strap, compared to the 1860-respirator strap, may be attributed to the hydrophobic nature of the strap. Hydrophobic layers ensure that the bulk of UV exposure occurs on the surface of respirators. In contrast, hygroscopic layers enhance the penetration of inoculum deeper into the textile, inhibiting the microorganisms from being adequately exposed to UV light. Figure 6 shows the overall structure for each of the tested respirator layers and depicts gaps in the material where droplets could reach. It is worth noting that since FFRs are single-use PPE items, the original design of the straps and choice of material was likely based on other desired features, such as comfort and durability. Incidentally, the pandemic has created a unique demand on the repurposing of FFRs (REF), and the strap material must be assessed in disinfection experiments as it appears to have a profound effect on UV disinfection efficiency. The findings presented in this manuscript provide evidence that respirators with hygroscopic properties may not be suitable for UV disinfection alone, as their absorbent materials may attract and retain droplets where microorganisms are present. Other studies have also found that different FFR models respond differently to UV disinfection 13 , 31 . However, comparison between FFR models and their material properties has not often been incorporated in previous studies, or their results have been inconclusive 37 , 38 . 3.5 Implications of UV disinfection on surfaces UV disinfection has been used primarily in the drinking water and wastewater industries since the maturation of the technology in the past decades 39 . More recently, UV technology has been increasingly used for disinfection of surfaces in hospital settings 40 – 42 . A recent study examined the impact of common hospital surfaces (plastic, stainless steel and copper) on UV disinfection efficiency 43 ; however, there is still a significant gap in UV surface disinfection knowledge. As mentioned by a recent study 44 , the applied UV fluence delivered onto a surface does not necessarily reflect the UV fluence received. Moreover, surface irregularities and crevices at the microscopic level could create shadowed areas where the UV light cannot penetrate. Furthermore, the porous multilayer structure of an N95 FFR requires roughly two orders of magnitude higher applied UV fluence for sufficient inactivation when compared to a smooth surface material. The COVID-19 pandemic has created an urgent need and interest to disinfect a broader range of complex surfaces, including N95 FFRs, surgical masks and other forms of PPE. This scenario presents a challenge for the development of disinfection protocols as there are many factors that can influence the effectiveness of UV treatment, such as surface geometry, material type and FFR construction. Recent studies have successfully applied UV technology for the repurposing of PPE in clinical settings 38 , 45 ; moreover, systematic reviews on the topic have concluded that UV disinfection is a suitable technology for PPE repurposing 12,44,46−48 . However, not all studies have considered the effect of different FFR layer materials on UV disinfection efficacy. While the current literature agrees that UV disinfection is suitable for FFR repurposing, there has not been a consensus on the UV fluence required. However, an application of at least 1000 mJ cm − 2 is the most common value reported 13 , 30 , 45 . Additionally, there is not unanimity on the required LRV to claim successful FFR disinfection, as these values have ranged from > 3 to > 6 LRV and involved different target microorganisms. Moreover, there is still debate whether the type of FFR material dictates the UV fluence required for disinfection, even though some studies have found evidence that the hydrophobicity/hydrophilicity of materials play a role in disinfection efficacy 13 , 30 , 49 . In contrast, other study 31 did not find a difference in disinfection performance between hydrophilic and hydrophobic materials used in FFR layers; however, the authors of the study did not provide a characterization of the materials. The inconsistency of results between studies for UV disinfection of FFRs could be attributed to the exclusion of the impact of respirator materials on disinfection performance. This work indicates that not all materials used in the construction of FFRs respond equally to UV treatment. To the author’s knowledge, this is the first manuscript that analyzes FFR disinfection efficiency as a function of layer material and composition when using a UV-C light source at 280 nm. It is hypothesized that differences in disinfection efficiency will be similarly impacted by material type across the UV-C spectrum. 3.6 Respirator layer analysis N95 FFRs are designed to repel droplets from the outer layers and electrostatically trap microorganisms within the respirator’s inner layers 50 . However, the reuse of N95 FFRs may still pose a health hazard to users if pathogenic microorganisms are not adequately inactivated. An experiment was conducted to assess several combinations of inter-layer MS2 inoculation and UV-C exposure direction at a fluence of 500 mJ cm − 2 . Figure 7 shows the differences in LRVs achieved. MS2 recoveries for 9210 FFR layers varied layer to layer, which impacted the level of measurable LRVs in many cases. Arrangements 3 and 5 were the only arrangements that used the front section of the 9210 FFR, which included L2 (Fig. 1 ). Tests with all other arrangements were carried out with the top section of the 9210 FFR, which did not include L2. The high LRVs for arrangements where embedded layers were inoculated were L3-a, depicted in Fig. 1 , was decisively the layer that blocked the most UV-C light. This can be concluded by the fact that arrangements 4 and 5 were the only arrangements that did not result in LRVs greater than 4. These results suggest that if 9210 FFRs are exposed to UV-C 280 nm from both sides, LRVs above 4 may be expected at fluences of 500 mJ cm − 2 . However, this may be a best-case scenario and does not account for areas on the respirator where additional blockage may occur, such as straps and nose pads. 4. Conclusions Filter facepiece respirators (FFR) models are comprised of different materials and numbers of layers; therefore, FFR models yield different log-removal values following UV treatment. The respirator layer that was selected for inoculation also impacted the disinfection efficacy of UV-C exposure. Additionally, the variability in FFR design invalidates a universal treatment approach for disinfection. Some respirator models may be suitable for decontamination and reuse using low levels of UV fluence, while other models need a much higher amount of irradiation to overcome material properties that inhibit UV exposure. Another important observation from this work was that not all sections of the respirator responded to UV treatment equally. The variety and complexity of materials used in the construction of FFRs results in a challenging surface to disinfect; for example, the straps of the 1860 model were highly resistant to disinfection (due to its intricate and hygroscopic PET nature), while higher LRVs were observed with the PDMS straps present on the 9210 FFR. A standardized protocol (in terms of inoculation volume, placement, cell-density, inoculum and FFR material) and reporting methodology for these results are also required to ensure safe and replicable decontamination. The authors recommend that the points mentioned in this paper are taken into consideration when designing testing and validation experiments using UV technology for FFR decontamination. Through this work, it is evident that the difference in material surface of N95 respirators will result in significant differences in UV disinfection efficacy and to maximize user safety, it is likely that only specific N95 respirators may be used for UV disinfection. The results presented in this study have implications for UV disinfection of materials, which extends to many possible applications well beyond respirator decontamination. Considering the high interest of surface disinfection, the results presented in this manuscript help the development of standardized protocols for the disinfection of complex materials using UV technology. 5. Declarations COMPETING INTERESTS The author(s) declare no competing interests. DATA AVAILABILITY The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. AUTHOR CONTRIBUTIONS C.C.O conceived, designed, and supervised the overall study, as well as data analysis and manuscript preparation. D.C.S contributed to the design of the study, produced, and analyzed laboratory data, manuscript preparation, and figures. S.M contributed with FTIR and SEM data collection, as well as with the preparation of figures. K.D.R. contributed to laboratory data collection and methodology development. C.L.S. reviewed and supervised manuscript preparation. A.K.S and G.A.G were the principal investigators, provided funding and research guidance. All authors contributed to revising the manuscript. All authors approved the submission of the final manuscript and agreed to be responsible for all aspects of the work. ACKNOWLEDGMENTS The authors acknowledge funding support from the NSERC COVID-19 Alliance Grant (Grant number ALLRP 549988-20) and the NSERC/Halifax Water Industrial Research Chair program (Grant number IRCPJ: 349838-16). Additionally, the authors acknowledge the Electron Microscopy Core Facility within the CORES program at Dalhousie University. The authors would also like to extend appreciation to Dr. Richard Simons (AquiSense Technologies) for technical advice and support during the project. The authors would also want to acknowledge the following researchers from the Centre for Water Resources Studies at Dalhousie University: Javier Locsin, Rishab Monga, Heather Daurie. 6. References Nogee, D. & Tomassoni, A. J. Covid-19 and the N95 respirator shortage: Closing the gap. Infect. Control Hosp. Epidemiol. 41 , 958–958 (2020). Hamzavi, I. H. et al. Ultraviolet germicidal irradiation: Possible method for respirator disinfection to facilitate reuse during the COVID-19 pandemic. Journal of the American Academy of Dermatology. 82 , 1511–1512 (2020). Lowe, J. et al. N95 Filtering Facepiece Respirator Ultraviolet Germicidal Irradiation (UVGI) Process for Decontamination and Reuse. 19 (2020). Czubryt, M. 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Boyce, J. M. & Donskey, C. J. Understanding ultraviolet light surface decontamination in hospital rooms: A primer. Infect. Control Hosp. Epidemiol. 40 , 1030–1035 (2019). Casini, B. et al. Evaluation of an Ultraviolet C (UVC) Light-Emitting Device for Disinfection of High Touch Surfaces in Hospital Critical Areas. IJERPH. 16 , 3572 (2019). Maguire, T. Ultraviolet Light Surface -Disinfecting Devices for Prevention of Hospital-Acquired Infections. A Health Technology Assessment. 18 , 73 (2018). Jureka, A. S., Williams, C. G. & Basler, C. F. Pulsed Broad-Spectrum UV Light Effectively Inactivates SARS-CoV-2 on Multiple Surfaces and N95 Material. Viruses. 13 , 460 (2021). Raeiszadeh, M. & Adeli, B. A. Critical Review on Ultraviolet Disinfection Systems against COVID-19 Outbreak: Applicability, Validation, and Safety Considerations. ACS Photonics. 7 , 2941–2951 (2020). Golladay, G. J. et al. Rationale and process for N95 respirator sanitation and re-use in the COVID-19 pandemic. Infect. Control Hosp. Epidemiol. 1–20 https://doi.org/10.1017/ice.2021.37 (2021). Schumm, M. A., Hadaya, J. E., Mody, N., Myers, B. A. & Maggard-Gibbons, M. Filtering Facepiece Respirator (N95 Respirator) Reprocessing: A Systematic Review. JAMA. https://doi.org/10.1001/jama.2021.2531 (2021). Torres, A. E. et al. Ultraviolet-C and other methods of decontamination of filtering facepiece N-95 respirators during the COVID-19 pandemic. Photochem. Photobiol. Sci. 19 , 746–751 (2020). Wharton, K. & Rieker, M. N95 Respirator Decontamination and Reuse: Current State of the Evidence. AANA Journal 6 (2020). Heimbuch, B. & Harnish, D. Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies(2019). Tcharkhtchi, A. et al. An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration. Bioactive Materials. 6 , 106–122 (2021). Additional Declarations No competing interests reported. Supplementary Files SUBMITTEDSupplementaryInformation.docx Cite Share Download PDF Status: Published Journal Publication published 28 Jul, 2021 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Major revision 11 Jun, 2021 Reviews received at journal 02 Jun, 2021 Reviewers agreed at journal 02 Jun, 2021 Reviewers agreed at journal 30 May, 2021 Reviewers invited by journal 27 May, 2021 Editor assigned by journal 27 May, 2021 Editor invited by journal 28 Apr, 2021 Submission checks completed at journal 28 Apr, 2021 First submitted to journal 17 Apr, 2021 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-435322\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":23758733,\"identity\":\"f594a3bb-2a67-4c36-91ca-636d4063adc2\",\"order_by\":0,\"name\":\"C. Carolina Ontiveros\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Dalhousie University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"C.\",\"middleName\":\"Carolina\",\"lastName\":\"Ontiveros\",\"suffix\":\"\"},{\"id\":23758734,\"identity\":\"ba64ff90-a9f7-49f2-9782-4d18624008e5\",\"order_by\":1,\"name\":\"David C. Shoults\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Dalhousie University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"David\",\"middleName\":\"C.\",\"lastName\":\"Shoults\",\"suffix\":\"\"},{\"id\":23758735,\"identity\":\"d8177065-039e-47a9-87a9-0a72016aab65\",\"order_by\":2,\"name\":\"Sean MacIsaac\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Dalhousie University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Sean\",\"middleName\":\"\",\"lastName\":\"MacIsaac\",\"suffix\":\"\"},{\"id\":23758736,\"identity\":\"2b114977-1a3d-473b-8ea7-30bb808b294d\",\"order_by\":3,\"name\":\"Kyle D. 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Note that side sections of the 9210 respirators lack an L2 layer.\",\"description\":\"\",\"filename\":\"groupimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-435322/v1/a7d4093ad64b99be251e073c.png\"},{\"id\":8657129,\"identity\":\"48459bca-1a96-492d-8314-2908275d8f93\",\"added_by\":\"auto\",\"created_at\":\"2021-04-30 19:25:47\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":17734,\"visible\":true,\"origin\":\"\",\"legend\":\"Inter-layer inoculation and UV exposure arrangements. Arrangements 1, 2, 4, \\u0026 6-8 represent the upper section of the 9210 FFR (comprised of L1 and L3). 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Each boxplot represents each of 2 technical replicates for each of 2 biological replicates.\",\"description\":\"\",\"filename\":\"Onlinefloatimage4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-435322/v1/fe7b94da6f376893709ea904.png\"},{\"id\":8657522,\"identity\":\"ed3e22a3-8677-460a-bbb7-403190b812e6\",\"added_by\":\"auto\",\"created_at\":\"2021-04-30 19:28:47\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":336555,\"visible\":true,\"origin\":\"\",\"legend\":\"Material characterization summary of the 1860, 8210 and 9210 N95 respirators. The left columns of SEM images for each respirator model are 55x magnification, and the right columns are 302x magnification. 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Introduction\",\"content\":\" \\u003cp\\u003eThere has been acute shortages of single-use N95 filter facepiece respirators (FFR) during the COVID-19 pandemic \\u003csup\\u003e\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e\\u003c/sup\\u003e. Consequently, an urgent call was made for suitable disinfection technologies for FFR reuse in response to shortages to overcome the critical need for PPE to ensure healthcare staff safety \\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e\\u003c/sup\\u003e. Some healthcare jurisdictions resorted to improvised FFR recycling programs where entire rooms were designated as spaces to expose used FFR to ultraviolet (UV) light to disinfect them for reuse \\u003csup\\u003e\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e\\u003c/sup\\u003e. The efficacy and suitability of several disinfection technologies have been investigated in recent years, including autoclaving, ethylene oxide (EtO), vaporized hydrogen peroxide (VHP), bleach, microwave irradiation, and UV irradiation \\u003csup\\u003e\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u003c/sup\\u003e. This study concluded that FFR disinfection by microwave oven and bleach were the least desirable due to melting of the respirator material and lingering smells of bleach, respectively. Additionally, UV irradiation is considered the most promising of the five disinfection approaches investigated by) due to throughput advantages over EtO and VHP \\u003csup\\u003e\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003eUV irradiation has been used in drinking water and wastewater treatment for decades, and more recently, has been shown to be effective for surface disinfection in food processing \\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR7\\\" citationid=\\\"CR6\\\" class=\\\"CitationRef\\\"\\u003e6\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR8\\\" class=\\\"CitationRef\\\"\\u003e8\\u003c/span\\u003e\\u003c/sup\\u003e and on other surfaces \\u003csup\\u003e\\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e9\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e10\\u003c/span\\u003e\\u003c/sup\\u003e. UV disinfection has several advantages over other disinfection methods due to its generally low environmental impacts, ease of use, and relatively small space requirements \\u003csup\\u003e\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e\\u003c/sup\\u003e. The suitability of UV disinfection as a germicidal process for more intricate materials (such as FFRs) is less understood. One of the limitations of UV treatment technologies is its ineffectiveness when light-shielding materials are present. UV shielding is particularly important when considering FFRs, as their surface geometry is complex and may lead to shaded areas that are not exposed to UV light. FFR geometry and material properties are hypothesized to play a role in shielding organisms from UV, resulting in reduced efficacy \\u003csup\\u003e\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u003c/sup\\u003e. Thus, there is a knowledge gap in understanding the interactions between UV light and complex surfaces and a need for further investigation to harness UV disinfection technologies for decontaminating FFR materials.\\u003c/p\\u003e \\u003cp\\u003eBefore the COVID-19 pandemic, data on UV disinfection of FFR was limited \\u003csup\\u003e\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e\\u003c/sup\\u003e. Previously conducted studies examining UV irradiation on FFRs are not current, contained methods that were difficult to compare with other studies, and required an update to fit the needs of the COVID-19 pandemic \\u003csup\\u003e5,13\\u0026minus;15\\u003c/sup\\u003e. Supply chain interruptions for personal protective equipment (PPE) led some jurisdictions to authorize emergency reuse of FFRs and other PPE, which resulted in an increase in studies investigating the efficacy of UV disinfection of these materials \\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e\\u003c/sup\\u003e. A recent surge of surface-UV exposure products brought to market for disinfecting FFRs, personal objects, and surfaces have resulted in additional measures by the U.S. Food and Drug Administration (FDA) to ensure consumer safety \\u003csup\\u003e\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e\\u003c/sup\\u003e. However, the guidelines provided by the FDA and the National Institute of Standards and Technology (NIST) are in their preliminary stage, and there is a lack of guidance towards best practices for validating FFR disinfection processes.\\u003c/p\\u003e \\u003cp\\u003eThe design of UV disinfection studies for FFRs requires careful consideration of several variables that may impact results. For example, the FFR model used, material layers selected for inoculation, and microorganism loading density must be considered. Further, in light of the public health significance of N95 respirators, disinfection studies must be carefully designed to minimize the number of respirators needed for research purposes. Accordingly, we designed an efficient experimental study with the aim of understanding the impact of multiple parameters on FFR material disinfection using UV irradiation. Experimental factors studied included UV fluence, test organism, inoculation concentration, inter-layer inoculation, and strap material. We also addressed the impact that FFR model type has on disinfection efficiency, which to date has not been sufficiently addressed in current literature.\\u003c/p\\u003e \"},{\"header\":\"2. Methods\",\"content\":\" \\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.1 Microbiological propagation and enumeration\\u003c/h2\\u003e \\u003cp\\u003eAll experiments were conducted with \\u003cem\\u003ePseudomonas aeruginosa\\u003c/em\\u003e PA01 and MS2 bacteriophage (ATCC 15597-B1) as performance surrogates for bacteria and viruses, respectively. For bacterial testing, tryptic soy broth (TSB) was inoculated with 100 \\u0026micro;L of overnight culture to create a 4-h subculture. \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e was enumerated using both the spread plate and membrane filtration methods on cetrimide agar, according to Standard Methods (D5465\\u0026ndash;16) \\u003csup\\u003e\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e\\u003c/sup\\u003e. Membrane filtration assays were performed using the entirety of sample solutions after volumes were removed for spread plating assays (~\\u0026thinsp;17.7 mL). MS2 was propagated and enumerated using the double-layer agar method on tryptic soy agar (TSA) with \\u003cem\\u003eEscherichia coli\\u003c/em\\u003e 3000 (ATCC 15597) as a host, according to Method 1601 \\u003csup\\u003e21\\u003c/sup\\u003e. Both \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e and MS2 agar plate assays were incubated for 18\\u0026ndash;24 h at 37\\u0026deg;C.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.2 FFR coupon inoculation, exposure, and recovery\\u003c/h2\\u003e \\u003cp\\u003eCoupons were made from 1-cm diameter material from 9210 and 8110s or 8210 (equivalents) N95 FFRs (3M, USA). N95 FFR strap coupons (1 cm\\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e\\u003c/sup\\u003e) were cut from 1860 and 8110s/8210 N95 FFRs (3M, USA). Before inoculation, \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e or MS2 working stocks were diluted into either phosphate buffer solution (PBS) or TSB to the desired concentration. In the single case when an extremely high \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e concentration was required, the working stock was centrifuged at 3,000 RPM for 10 min and resuspended in TSB. Depending on the experiment, duplicate or triplicate respirator material coupons or strap sections were placed inside sterile 47-mm Petri dishes and inoculated with the diluted \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e or MS2 by pipetting 5-\\u0026micro;L droplets onto the surface of the coupon. Droplets were then spread with a cooled flame-sterilized glass spreader and allowed to dry for 20 min. The estimated loadings are reported as colony-forming units (CFU) or plaque-forming units (PFU) per cm\\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e\\u003c/sup\\u003e (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003ePetri dishes containing inoculated coupon samples were placed 1.5 cm beneath the collimator onto a 30 RPM rotating platform with the inoculated surface facing up to ensure uniform UV exposure. Following exposure, each FFR coupon was placed in a sterile 50-mL conical tube containing 20 mL sterile PBS using flame-sterilized tweezers. Each strap coupon was placed in a sterile 2-mL dilution tube containing 0.9 mL sterile PBS. For both sample types, tubes containing samples were vortexed at 3000 RPM for 1 min to facilitate the shedding of microorganisms. The resulting liquid suspension from each sample, referred to as sample solution, was then used for serial dilutions or plated directly from the sample solution. For both spread plating and the double-layer agar method, serially diluted 100-\\u0026micro;L samples were plated. In cases where high inactivation levels were anticipated, 1 mL of undiluted MS2 and \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e sample solutions were plated.\\u003c/p\\u003e \\u003cp\\u003eAdditionally, \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e sample solutions were used for membrane filtration plating of \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e. For each variable parameter (\\u003cem\\u003ei.e\\u003c/em\\u003e., concentration, respirator material), positive controls (no UV exposure) were prepared for comparison with treated samples for log reduction value (LRV) estimation. Positive control recovery was carried out as described above, absent UV exposure.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec5\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.3 UV collimated beam apparatus\\u003c/h2\\u003e \\u003cp\\u003eUV inactivation experiments were conducted using the 280 nm wavelength on a UV-C LED collimated beam apparatus (PearlLab Beam T 255/280/365, Aquisense, USA). Irradiance was measured using a USB4000 Ocean Optics spectroradiometer (Ocean Optics, USA). Irradiance measurements were collected with 0.5-mm spatial resolution across the face of the coupons and were used to calculate the Petri Factor (0.890). The average irradiance delivered to FFR coupons was determined using the product of a central irradiance measurement and the Petri Factor and was calculated to be 794 \\u0026micro;W cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. The desired fluence was divided by the average irradiance to determine the required exposure time.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec6\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.4 Intra-Layer Inoculation\\u003c/h2\\u003e \\u003cp\\u003eN95 respirators are composed of multiple layers. The 9210 FFR (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003eb) is composed of an outer hydrophobic layer (L1), a middle electrostatically charged layer (L2), and an inner biocompatible layer (L3), as described by a previous study\\u003csup\\u003e\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e\\u003c/sup\\u003e. L3 was dissected into three sub-layers (a, b, \\u0026amp; c) to investigate the nature of the respirator material further. The hydrophobic nature of N95 respirator material is intended to repel 95% of aerosolized droplets; however, droplet nuclei may penetrate the outer hydrophobic layer and become trapped in the electrostatic layers of the material. An inter-layer study was conducted using coupons cut from the N95-9210 FFR model to investigate differences in the reduction of organisms that may be present within FFR layers. Eight combinations of inter-layer inoculation and UV-C exposure direction were investigated. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e illustrates the layer configuration and labelling scheme. All arrangements were exposed to 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e of UV-C 280 nm.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eCoupon layers were peeled back using flame-sterilized tweezers and inoculated as described in Sect.\\u0026nbsp;2.4. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e illustrates the eight combinations of inter-layer inoculation location and exposure direction.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec7\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.5 Respirator layer analysis\\u003c/h2\\u003e \\u003cp\\u003eMaterial characterization was conducted on different respirator models to analyze the different respirator layers and their role in disinfection efficacy. Layers and straps of N95 respirator models 9205, 9210, 8210, 1804, and 1860 were characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Samples of FFR layers and straps from each of the models were treated with gold sputtering and then scanned at 302 and 55x magnification. FTIR measures the infrared absorption and emission spectra of the sample and infers the functional groups present. An FTIR (Bruker Alpha, USA) equipped with the solid-phase attachment was used for all samples. For FTIR analysis, only N95 1860, 8210 and 9210 models are presented in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e. Material characterization information for additional respirator models can be found in Supplementary Figure S2. FTIR samples were prepared by cutting a 1-cm\\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e\\u003c/sup\\u003e coupon from each respirator layer and placing them beneath the FTIR instrument head. Sample spectra were matched with profiles from the Bruker library to identify the most probable material type. Spectra were then exported as CSV files for further data management using the R programming environment. Results can be found in Supplementary Figure S3.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec8\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.6 Irradiance through 9210 FFR layers\\u003c/h2\\u003e \\u003cp\\u003eUV light penetration through the N95 9210 respirator layers was tested using the UV-C LED collimated beam apparatus (PearlLab Beam T 255/280/365, Aquisense, USA). The UV light was measured using a USB4000 spectrometer (Ocean Optics Inc., USA) to determine the proportion of UV light blocked by the layers of the 9210 respirators. Light penetration was assessed by clipping combinations of coupons of 9210 respirator layers to the surface of a spectroradiometer detector as described in a previous study\\u003csup\\u003e\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec9\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.7 Replicates, limits of detection and quantification, statistics, and data visualization\\u003c/h2\\u003e \\u003cp\\u003eFor each experiment, a minimum of two biological replicates (\\u003cem\\u003ei.e.\\u003c/em\\u003e, two coupons) was performed for each combination of variables (\\u003cem\\u003ei.e.\\u003c/em\\u003e, fluence, respirator layer). Each biological replicate was enumerated \\u003cem\\u003evia\\u003c/em\\u003e two technical replicates (\\u003cem\\u003ei.e.\\u003c/em\\u003e, two assays) across a minimum of three 10-fold dilutions for spread-plating (\\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e) and the double-layer agar (MS2) assays. A single membrane filtration assay was performed for each biological replicate of treated \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e samples. Positive controls were processed for each experiment, including separate sets of controls when different materials, layers, or concentrations were investigated. All data were analyzed and visualized using R v4.0.0 and RStudio v1.1.463 \\u003csup\\u003e22\\u003c/sup\\u003e using the Tidyverse \\u003csup\\u003e\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e\\u003c/sup\\u003e, Ggplot2 \\u003csup\\u003e24\\u003c/sup\\u003e, Dplyr \\u003csup\\u003e\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e\\u003c/sup\\u003e, Ggsci \\u003csup\\u003e\\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e\\u003c/sup\\u003e and RColorBrewer \\u003csup\\u003e\\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e27\\u003c/span\\u003e\\u003c/sup\\u003e packages. For both \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e and MS2, non-detects (ND) were \\u0026lt;\\u0026thinsp;1 CFU/PFU per maximum volume plated. Where appropriate, paired t-tests were conducted at a significance level of α\\u0026thinsp;=\\u0026thinsp;0.05. When comparing UV fluences, one-sided t-tests were performed. In all other cases, two-sided t-tests were performed.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec10\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.8 Experimental design\\u003c/h2\\u003e \\u003cp\\u003eA fluence of 50 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e was used to test the UV-C efficacy of four \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e loading concentrations. Preliminary experimentation (data not shown) suggested that in some instances, 100 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e was sufficient to reduce \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e to below detection; therefore, a fluence of 50 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e was chosen to measure disparities in LRVs between different loading concentrations. The loading concentrations are described in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003eUV-C (280 nm) light blockage was investigated using various layer combinations for both the 9210 and 8110s N95 models. Respirator layers were fastened on top of the spectrometer, then placed below the collimated beam. Thirty irradiation readings were taken per layer combination and averaged. These values were then compared to the averaged readings taken when no layers were present between the UV-C light source and spectrometer to estimate the percentage of 280 nm light blocked by each layer or layer combination.\\u003c/p\\u003e \\u003cp\\u003eFor clarity, a summary of all experiments is detailed in Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e, which includes the objective, test-organism, layer-exposure arrangement (see Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e), fluences, coupon/elastic material, biological replicates, and microorganism loading.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003eExperimental summary of organism, inoculation concentration, FFR material, exposure arrangement, fluences, and replicates\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"7\\\"\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eObjective\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eOrganism\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003eInoculation concentration (CFU/PFU cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003eFFR Material\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eLayer-exposure arrangement \\u003c/p\\u003e \\u003cp\\u003e(Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003eUV-C fluences \\u003c/p\\u003e \\u003cp\\u003e(mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003eBiological replicates\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"2\\\" rowspan=\\\"3\\\"\\u003e \\u003cp\\u003eFluence response (coupon)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMS2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e6.9E\\u0026thinsp;+\\u0026thinsp;08\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1 \\u0026amp; 8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0, 50, 100, 500, 700, 1000\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2 per fluence per arrangement\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMS2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e6.9E\\u0026thinsp;+\\u0026thinsp;08\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e8110s/8210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1 \\u0026amp; 8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0, 100, 500, 1000\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2 per fluence per arrangement\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e3.9E\\u0026thinsp;+\\u0026thinsp;06\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0, 100, 500, 1000\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e3 per fluence\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003eFluence response (straps)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003eMS2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003e6.9E\\u0026thinsp;+\\u0026thinsp;08\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210 (rubber)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eDirect\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0, 50, 100, 500, 700, 1000\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2 per fluence\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e1860 (polyester)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003eDirect\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0, 50, 100, 500, 700, 1000, 1400*\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2 per fluence\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003eBacterial loading (coupon)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e4.0E\\u0026thinsp;+\\u0026thinsp;03\\u003c/p\\u003e \\u003cp\\u003e4.0E\\u0026thinsp;+\\u0026thinsp;04\\u003c/p\\u003e \\u003cp\\u003e3.2E\\u0026thinsp;+\\u0026thinsp;05\\u003c/p\\u003e \\u003cp\\u003e1.6E\\u0026thinsp;+\\u0026thinsp;06\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0 and 50\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e3 per fluence per concentration\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e1.6E\\u0026thinsp;+\\u0026thinsp;06\\u003c/p\\u003e \\u003cp\\u003e5.0E\\u0026thinsp;+\\u0026thinsp;07\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0 and 1000\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e3 per fluence per concentration\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eInter-layer inoculation\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eMS2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e6.9E\\u0026thinsp;+\\u0026thinsp;08\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9210\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1\\u0026ndash;8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e0 and 500\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2 per fluence per arrangement\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003ctfoot\\u003e \\u003ctr\\u003e\\u003ctd colspan=\\\"7\\\"\\u003e*The polyester elastic absorbed the inoculation liquid; therefore, the elastic was flipped over after 700 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e to expose both sides.\\u003c/td\\u003e\\u003c/tr\\u003e \\u003c/tfoot\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec11\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.9 Control experiments\\u003c/h2\\u003e \\u003cp\\u003eSince it is not common to combine spread plating and membrane filtration for enumeration comparison, as they may vary in accuracy and precision, a recovery experiment was performed to determine if there was a significant difference in recovery efficiency between the two methods. To do so, \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e was assayed \\u003cem\\u003evia\\u003c/em\\u003e both enumeration techniques with 12 replicates for both. The results of these experiments can be found in SI 1.\\u003c/p\\u003e \\u003c/div\\u003e \"},{\"header\":\"3. Results And Discussion\",\"content\":\" \\u003cdiv id=\\\"Sec13\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.1 Effects of respirator material and UV-C fluence\\u003c/h2\\u003e \\u003cp\\u003eCoupons from two 3M N95 respirator models (8110s \\u0026amp; 9210) were inoculated with MS2 and exposed to an array of UV-C 280 nm fluences ranging from 50 to 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e to examine the relative effects of fluence and type of respirator material. The results of this experiment are shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eFFR model 9210\\u003c/em\\u003e \\u003c/p\\u003e \\u003cp\\u003eAt 50, 100, and 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e), MS2 LRVs observed for the 9210 FFR differed significantly between L1 and L3 (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.0009, 0.01, \\u0026amp; 0.01, respectively). At fluences of 700 and 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, no significant difference in MS2 reduction was observed between L1 and L3 (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.9 \\u0026amp; 0.07, respectively). This difference suggests that the outer-most layer (L1) requires a higher UV-C fluence for inactivation. For L1, MS2 LRV increases between fluences were significant up until 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, after which no significant differences were observed. For L3, LRV increases were significant between 50 and 100 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.02), after which no significant increases in LRV were observed. In Supplementary Figure S1, \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e LRVs observed for 9210-L1 were similar to that observed with MS2. The similarity in kinetics between MS2 and \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e was surprising, given that MS2 typically requires UV fluences which are orders of magnitude higher than what is required for a similar LRV of \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e \\u003csup\\u003e\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e29\\u003c/span\\u003e\\u003c/sup\\u003e. Supplementary Figure S1 illustrates an observable difference in \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e LRVs between 100 and 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. Between 500 and 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, the LRVs were virtually the same, both having two treated samples with non-detectable levels of \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eFFR model 8110s/8210\\u003c/em\\u003e \\u003c/p\\u003e \\u003cp\\u003eA significant difference in LRV was observed between L1 and L3 of the 8110s FFR at 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.02) but not at 100 and 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.3 for both fluences). Further, there was no significant increase in LRV at fluences after 100 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;\\u0026gt;\\u0026thinsp;0.05). The most drastic LRV differences were observed between the 9210 and 8110s respirator models. Significant differences (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;\\u0026lt;\\u0026thinsp;\\u0026lt;\\u0026thinsp;0.05) were observed between both respirator models for both arrangements and all paired fluences (100, 500, \\u0026amp; 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e).\\u003c/p\\u003e \\u003cp\\u003eThe disparities in LRV observed between the two respirator models are consistent with previous studies \\u003csup\\u003e\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e\\u003c/sup\\u003e, who found that the effectiveness of various decontamination methods was model-dependent, given their differences in design, materials, and hydrophobicity. However, a more recent study\\u003csup\\u003e\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e\\u003c/sup\\u003e did not find a statistical difference between hydrophobic versus hydrophilic respirator materials. In summary, the outer-most layer (L1) of the 9210 FFR requires higher UV-C fluences than the inner-most layer (L3) to reach the maximum observed MS2 LRV of just over 5. Additionally, UV is considerably more effective for inactivating MS2 on 9210 FFRs relative to 8110s FFRs and higher than 5 LRVs on MS2 are achievable at UV-C 280 nm fluences of 100 and 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e for L3 and L1 of the 9210 FFR, respectively.\\u003c/p\\u003e \\u003cp\\u003eAs shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e, both respirator models and the inoculation/exposure arrangement considerably affected UV efficacy. Although both FFR models are comparable in terms of certification by The National Institute for Occupational Safety and Health (NIOSH), they responded differently in terms of UV disinfection. LRVs above 1.5 were not observed with the 8110s/8210 FFR model, even at fluences of 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. The 9210 FFR model resulted in a more pronounced disinfection curve, where LRVs between 5 and 6 were observed for both L1 and L3 starting at doses of 500 and 100 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, respectively. Proposed stringent regulations of 3 and 6 LRVs \\u003csup\\u003e\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e32\\u003c/span\\u003e\\u003c/sup\\u003e for Tier 3 and Tier 2 certification, respectively; however, these results suggest that UV disinfection technologies may behold specificity for FFR models, which is not contemplated in regulatory constructs. Future UV validation studies for FFR disinfection should place emphasis on the model of FFR investigated to understand disinfection efficacy and specificity further.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec14\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.2 FFR elastic material and UV-C fluence\\u003c/h2\\u003e \\u003cp\\u003eStrap segments from two FFR models were inoculated with MS2 and exposed to UV-C irradiation at fluences of 280-nm. The objectives were to i) understand the UV-C kinetics for MS2 on FFR straps and ii) determine if strap material plays a role in UV efficacy for treating FFR straps. Rubber-elastic (9210) and polyester-elastic (1860) straps were tested. The LRVs observed with the rubber elastic from the 9210 FFR increased steadily until 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, where all samples were reduced to either below the LOQ or below detection. However, the LRVs observed with the polyester elastic from the 1860 FFR were considerably less. LRVs remained at or below 0.5 for fluences of 50 to 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. When each side of the elastic was exposed to 700 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e for a total of 1,400 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, LRVs were higher than when one side was exposed to 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e; however, the difference was relatively small (0.17, \\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;0.003).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eFigure \\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e shows that similarly to the 9210-respirator material, MS2 LRVs\\u0026thinsp;\\u0026gt;\\u0026thinsp;5 are observed at a fluence of 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e for 9210 rubber-elastic straps. When treating the polyester-elastic 1860 respirator straps, it was impossible to achieve more than one LRV, even when exposed to UV-C fluences higher than 1,000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, which are generally sufficient under other conditions. Additionally, even when the 1860 polyester straps were exposed to UV-C fluences (700 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e per side), LRVs were not substantially increased. SEM results (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e) show that the polyester strap is much more intricate at a microscopic level than the rubber strap from other FFR models. This intricate geometry is likely absorbing the inoculum and preventing UV-C radiation from penetrating the strap material, in contrast with rubber straps where the inoculum droplets stay on top of the material.\\u003c/p\\u003e \\u003cp\\u003eIncluding strap material in disinfection experiments is critical to determine if specific N95 FFRs models will be suitable candidates for a given disinfection strategy. The results presented in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e show that the 1860 FFR model and any other model with polyester nature straps may not be suitable for UV-C disinfection, at least below an applied fluence of 1,400 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec15\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.3 Effects of bacterial loading\\u003c/h2\\u003e \\u003cp\\u003eThe relative effects of microbial concentrations on disinfection performance are not well understood, especially concerning FFR materials. For this reason, we investigated the relative effects of \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e cell-density inoculated onto 9210 FFR coupons on LRVs (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e was recovered at similar concentrations in treated samples (\\u003cem\\u003ep\\u003c/em\\u003e\\u0026thinsp;\\u0026lt;\\u0026thinsp;0.05 for all comparisons) across all cell-densities examined, resulting in an increased LRV as cell-densities increased (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e). Increased cell-densities that would result in more significant shielding were expected but were not observed in this result. The data in this study suggest that if cell-densities are too low, there is a diminishing return in efficacy with respect to LRVs. The implications of these results are essential for the design of standardized performance-testing protocols. Furthermore, a more direct comparison between studies would be possible if cell-densities were reported. For example, a recent study \\u003csup\\u003e\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e\\u003c/sup\\u003e achieved\\u0026thinsp;\\u0026gt;\\u0026thinsp;5 LRV with MS2, whereas other studies \\u003csup\\u003e\\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e,33\\u003c/sup\\u003eonly achieved around 3 LRV with MS2 as well. None of these studies mentioned cell density; additionally, inoculation medium, FFR model used, and inoculation technique was also different. These disparity among studies may be impacted by cell-densities or other factors that were different, such as respirator type and inoculation location, as shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e.\\u003c/p\\u003e \\u003cp\\u003eA second experiment was conducted to address potential differences at higher cell-densities and a higher UV-C 280-nm fluence. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e, there may exist a critical cell-density threshold somewhere between 6.2 and 7.7 log CFU cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e, in which cell-densities exceeding such a threshold result in over-aggregation of bacterial cells, leading to reduced LRVs.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec16\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.4 Materials characterization of three N95 FFR models\\u003c/h2\\u003e \\u003cp\\u003eFigure \\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e summarizes the material characterization of the 1860, 8210 and 9210 N95 respirators. Only the three primary and more easily separated layers were analyzed. Layer nomenclature is as depicted in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003eA. The main polymers found in the layers of the respirator were Polypropylene (PP), Polyethylene Terephthalate (PET-P), Polydimethylsiloxane (PDMS), and Eltec P HP-603 Polypropylene.\\u003c/p\\u003e \\u003cp\\u003ePP is considered a thermoplastic polymer used in a wide range of applications. PP presents non-polar properties, which indicates a low interaction with water \\u003csup\\u003e\\u003cspan citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e34\\u003c/span\\u003e\\u003c/sup\\u003e. In contrast, PET is a polar plastic, commonly found in plastic bottles \\u003csup\\u003e\\u003cspan citationid=\\\"CR35\\\" class=\\\"CitationRef\\\"\\u003e35\\u003c/span\\u003e\\u003c/sup\\u003e. PET has an intrinsic viscosity and hygroscopic nature (retains water from its surroundings). Moreover, PDMS is a commercially-available silicon rubber \\u003csup\\u003e\\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e36\\u003c/span\\u003e\\u003c/sup\\u003e that is viscoelastic and hydrophobic (repels water).\\u003c/p\\u003e \\u003cp\\u003eThe 1860 model layers were mainly comprised of PP (L1 and L2) and PET (L3), while the straps were composed of PET. Comparatively, the 9210 model mainly had PP (L1, L2 and L3) and PDMS (rubber) for the straps, while the 8210 model primarily consisted of PET (L1 and L3), Eltec P HP-603 Polypropylene (L2), and Bunatex K 71 (straps).\\u003c/p\\u003e \\u003cp\\u003eThe respirator materials and their configuration within the layers of the respirators could explain the difference in disinfection found in the respirator microbial testing. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e and Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e show that the 9210 respirator achieved higher LRVs in both MS2 and \\u003cem\\u003eP. aeruginosa\\u003c/em\\u003e tests. The 9210 and 1860 respirator models have a more plastic feel on L1 than the 8210 model, which has a softer and more fabric-like texture.\\u003c/p\\u003e \\u003cp\\u003eThe 1860 respirator straps, which have a fabric-like texture, resulted in low LRVs compared to the 9210 model, even when applying 700 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e per side. The low LRV value achieved on the 1860 strap may be attributed to the hygroscopic nature of PET, contrary to the 9210-respirator strap, which is mainly composed of hydrophobic PDMS.\\u003c/p\\u003e \\u003cp\\u003eThe higher disinfection efficiency on the 9210 respirator strap, compared to the 1860-respirator strap, may be attributed to the hydrophobic nature of the strap. Hydrophobic layers ensure that the bulk of UV exposure occurs on the surface of respirators. In contrast, hygroscopic layers enhance the penetration of inoculum deeper into the textile, inhibiting the microorganisms from being adequately exposed to UV light. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e shows the overall structure for each of the tested respirator layers and depicts gaps in the material where droplets could reach. It is worth noting that since FFRs are single-use PPE items, the original design of the straps and choice of material was likely based on other desired features, such as comfort and durability. Incidentally, the pandemic has created a unique demand on the repurposing of FFRs (REF), and the strap material must be assessed in disinfection experiments as it appears to have a profound effect on UV disinfection efficiency.\\u003c/p\\u003e \\u003cp\\u003eThe findings presented in this manuscript provide evidence that respirators with hygroscopic properties may not be suitable for UV disinfection alone, as their absorbent materials may attract and retain droplets where microorganisms are present. Other studies have also found that different FFR models respond differently to UV disinfection \\u003csup\\u003e\\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e\\u003c/sup\\u003e. However, comparison between FFR models and their material properties has not often been incorporated in previous studies, or their results have been inconclusive \\u003csup\\u003e\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003e37\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR38\\\" class=\\\"CitationRef\\\"\\u003e38\\u003c/span\\u003e\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec17\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.5 Implications of UV disinfection on surfaces\\u003c/h2\\u003e \\u003cp\\u003eUV disinfection has been used primarily in the drinking water and wastewater industries since the maturation of the technology in the past decades \\u003csup\\u003e\\u003cspan citationid=\\\"CR39\\\" class=\\\"CitationRef\\\"\\u003e39\\u003c/span\\u003e\\u003c/sup\\u003e. More recently, UV technology has been increasingly used for disinfection of surfaces in hospital settings \\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR41\\\" citationid=\\\"CR40\\\" class=\\\"CitationRef\\\"\\u003e40\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR42\\\" class=\\\"CitationRef\\\"\\u003e42\\u003c/span\\u003e\\u003c/sup\\u003e. A recent study examined the impact of common hospital surfaces (plastic, stainless steel and copper) on UV disinfection efficiency \\u003csup\\u003e\\u003cspan citationid=\\\"CR43\\\" class=\\\"CitationRef\\\"\\u003e43\\u003c/span\\u003e\\u003c/sup\\u003e; however, there is still a significant gap in UV surface disinfection knowledge. As mentioned by a recent study\\u003csup\\u003e\\u003cspan citationid=\\\"CR44\\\" class=\\\"CitationRef\\\"\\u003e44\\u003c/span\\u003e\\u003c/sup\\u003e, the applied UV fluence delivered onto a surface does not necessarily reflect the UV fluence received. Moreover, surface irregularities and crevices at the microscopic level could create shadowed areas where the UV light cannot penetrate. Furthermore, the porous multilayer structure of an N95 FFR requires roughly two orders of magnitude higher applied UV fluence for sufficient inactivation when compared to a smooth surface material.\\u003c/p\\u003e \\u003cp\\u003eThe COVID-19 pandemic has created an urgent need and interest to disinfect a broader range of complex surfaces, including N95 FFRs, surgical masks and other forms of PPE. This scenario presents a challenge for the development of disinfection protocols as there are many factors that can influence the effectiveness of UV treatment, such as surface geometry, material type and FFR construction. Recent studies have successfully applied UV technology for the repurposing of PPE in clinical settings \\u003csup\\u003e\\u003cspan citationid=\\\"CR38\\\" class=\\\"CitationRef\\\"\\u003e38\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR45\\\" class=\\\"CitationRef\\\"\\u003e45\\u003c/span\\u003e\\u003c/sup\\u003e; moreover, systematic reviews on the topic have concluded that UV disinfection is a suitable technology for PPE repurposing \\u003csup\\u003e12,44,46\\u0026minus;48\\u003c/sup\\u003e. However, not all studies have considered the effect of different FFR layer materials on UV disinfection efficacy.\\u003c/p\\u003e \\u003cp\\u003eWhile the current literature agrees that UV disinfection is suitable for FFR repurposing, there has not been a consensus on the UV fluence required. However, an application of at least 1000 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e is the most common value reported \\u003csup\\u003e\\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR45\\\" class=\\\"CitationRef\\\"\\u003e45\\u003c/span\\u003e\\u003c/sup\\u003e. Additionally, there is not unanimity on the required LRV to claim successful FFR disinfection, as these values have ranged from \\u0026gt;\\u0026thinsp;3 to \\u0026gt;\\u0026thinsp;6 LRV and involved different target microorganisms. Moreover, there is still debate whether the type of FFR material dictates the UV fluence required for disinfection, even though some studies have found evidence that the hydrophobicity/hydrophilicity of materials play a role in disinfection efficacy \\u003csup\\u003e\\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR49\\\" class=\\\"CitationRef\\\"\\u003e49\\u003c/span\\u003e\\u003c/sup\\u003e. In contrast, other study \\u003csup\\u003e31\\u003c/sup\\u003edid not find a difference in disinfection performance between hydrophilic and hydrophobic materials used in FFR layers; however, the authors of the study did not provide a characterization of the materials.\\u003c/p\\u003e \\u003cp\\u003eThe inconsistency of results between studies for UV disinfection of FFRs could be attributed to the exclusion of the impact of respirator materials on disinfection performance. This work indicates that not all materials used in the construction of FFRs respond equally to UV treatment. To the author\\u0026rsquo;s knowledge, this is the first manuscript that analyzes FFR disinfection efficiency as a function of layer material and composition when using a UV-C light source at 280 nm. It is hypothesized that differences in disinfection efficiency will be similarly impacted by material type across the UV-C spectrum.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec18\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e3.6 Respirator layer analysis\\u003c/h2\\u003e \\u003cp\\u003eN95 FFRs are designed to repel droplets from the outer layers and electrostatically trap microorganisms within the respirator\\u0026rsquo;s inner layers \\u003csup\\u003e\\u003cspan citationid=\\\"CR50\\\" class=\\\"CitationRef\\\"\\u003e50\\u003c/span\\u003e\\u003c/sup\\u003e. However, the reuse of N95 FFRs may still pose a health hazard to users if pathogenic microorganisms are not adequately inactivated. An experiment was conducted to assess several combinations of inter-layer MS2 inoculation and UV-C exposure direction at a fluence of 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. Figure\\u0026nbsp;\\u003cspan refid=\\\"Fig7\\\" class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e shows the differences in LRVs achieved.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eMS2 recoveries for 9210 FFR layers varied layer to layer, which impacted the level of measurable LRVs in many cases. Arrangements 3 and 5 were the only arrangements that used the front section of the 9210 FFR, which included L2 (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e). Tests with all other arrangements were carried out with the top section of the 9210 FFR, which did not include L2.\\u003c/p\\u003e \\u003cp\\u003eThe high LRVs for arrangements where embedded layers were inoculated were L3-a, depicted in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e, was decisively the layer that blocked the most UV-C light. This can be concluded by the fact that arrangements 4 and 5 were the only arrangements that did not result in LRVs greater than 4. These results suggest that if 9210 FFRs are exposed to UV-C 280 nm from both sides, LRVs above 4 may be expected at fluences of 500 mJ cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;2\\u003c/sup\\u003e. However, this may be a best-case scenario and does not account for areas on the respirator where additional blockage may occur, such as straps and nose pads.\\u003c/p\\u003e \\u003c/div\\u003e \"},{\"header\":\"4. Conclusions\",\"content\":\" \\u003cp\\u003eFilter facepiece respirators (FFR) models are comprised of different materials and numbers of layers; therefore, FFR models yield different log-removal values following UV treatment. The respirator layer that was selected for inoculation also impacted the disinfection efficacy of UV-C exposure. Additionally, the variability in FFR design invalidates a universal treatment approach for disinfection. Some respirator models may be suitable for decontamination and reuse using low levels of UV fluence, while other models need a much higher amount of irradiation to overcome material properties that inhibit UV exposure. Another important observation from this work was that not all sections of the respirator responded to UV treatment equally. The variety and complexity of materials used in the construction of FFRs results in a challenging surface to disinfect; for example, the straps of the 1860 model were highly resistant to disinfection (due to its intricate and hygroscopic PET nature), while higher LRVs were observed with the PDMS straps present on the 9210 FFR.\\u003c/p\\u003e \\u003cp\\u003eA standardized protocol (in terms of inoculation volume, placement, cell-density, inoculum and FFR material) and reporting methodology for these results are also required to ensure safe and replicable decontamination. The authors recommend that the points mentioned in this paper are taken into consideration when designing testing and validation experiments using UV technology for FFR decontamination. Through this work, it is evident that the difference in material surface of N95 respirators will result in significant differences in UV disinfection efficacy and to maximize user safety, it is likely that only specific N95 respirators may be used for UV disinfection. The results presented in this study have implications for UV disinfection of materials, which extends to many possible applications well beyond respirator decontamination. Considering the high interest of surface disinfection, the results presented in this manuscript help the development of standardized protocols for the disinfection of complex materials using UV technology.\\u003c/p\\u003e \"},{\"header\":\"5. Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eCOMPETING INTERESTS\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe author(s) declare no competing interests.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eDATA AVAILABILITY\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAUTHOR CONTRIBUTIONS\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eC.C.O conceived, designed, and supervised the overall study, as well as data analysis and manuscript preparation. D.C.S contributed to the design of the study, produced, and analyzed laboratory data, manuscript preparation, and figures. S.M contributed with FTIR and SEM data collection, as well as with the preparation of figures. K.D.R. contributed to laboratory data collection and methodology development. C.L.S. reviewed and supervised manuscript preparation. A.K.S and G.A.G were the principal investigators, provided funding and research guidance. All authors contributed to revising the manuscript. All authors approved the submission of the final manuscript and agreed to be responsible for all aspects of the work.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eACKNOWLEDGMENTS\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors acknowledge funding support from the NSERC COVID-19 Alliance Grant (Grant number ALLRP 549988-20) and the NSERC/Halifax Water Industrial Research Chair program (Grant number IRCPJ: 349838-16). Additionally, the authors acknowledge the Electron Microscopy Core Facility within the CORES program at Dalhousie University. The authors would also like to extend appreciation to Dr. Richard Simons (AquiSense Technologies) for technical advice and support during the project. The authors would also want to acknowledge the following researchers from the Centre for Water Resources Studies at Dalhousie University: Javier Locsin, Rishab Monga, Heather Daurie.\\u003c/p\\u003e\"},{\"header\":\"6. References\",\"content\":\"\\u003col\\u003e\\u003cli\\u003e\\u003cspan\\u003eNogee, D. \\u0026amp; Tomassoni, A. J. Covid-19 and the N95 respirator shortage: Closing the gap. \\u003cem\\u003eInfect. Control Hosp. Epidemiol.\\u003c/em\\u003e \\u003cb\\u003e41\\u003c/b\\u003e, 958\\u0026ndash;958 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eHamzavi, I. H. \\u003cem\\u003eet al.\\u003c/em\\u003e Ultraviolet germicidal irradiation: Possible method for respirator disinfection to facilitate reuse during the COVID-19 pandemic. \\u003cem\\u003eJournal of the American Academy of Dermatology.\\u003c/em\\u003e \\u003cb\\u003e82\\u003c/b\\u003e, 1511\\u0026ndash;1512 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eLowe, J. \\u003cem\\u003eet al.\\u003c/em\\u003e N95 Filtering Facepiece Respirator Ultraviolet Germicidal Irradiation (UVGI) Process for Decontamination and Reuse. 19 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eCzubryt, M. 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D., Tvede, M., Begovic, T. \\u0026amp; Gregersen, A. Dose requirements for UVC disinfection of catheter biofilms. \\u003cem\\u003eBiofouling.\\u003c/em\\u003e \\u003cb\\u003e25\\u003c/b\\u003e, 289\\u0026ndash;296 (2009).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eU.S. EPA. \\u003cem\\u003eWastewater technology fact sheet - Disinfection for small systems\\u003c/em\\u003e. (1999).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eSeresirikachorn, K. \\u003cem\\u003eet al.\\u003c/em\\u003e Decontamination and reuse of surgical masks and N95 filtering facepiece respirators during the COVID-19 pandemic: A systematic review. \\u003cem\\u003eInfect. Control Hosp. Epidemiol.\\u003c/em\\u003e \\u003cb\\u003e42\\u003c/b\\u003e, 25\\u0026ndash;30 (2021).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eFisher, E. M. \\u0026amp; Shaffer, R. E. A method to determine the available UV-C dose for the decontamination of filtering facepiece respirators: UV-C decontamination of respirators. \\u003cem\\u003eJournal of Applied Microbiology.\\u003c/em\\u003e \\u003cb\\u003e110\\u003c/b\\u003e, 287\\u0026ndash;295 (2011).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eHeimbuch, B. K. \\u003cem\\u003eet al.\\u003c/em\\u003e A pandemic influenza preparedness study: Use of energetic methods to decontaminate filtering facepiece respirators contaminated with H1N1 aerosols and droplets. \\u003cem\\u003eAmerican Journal of Infection Control.\\u003c/em\\u003e \\u003cb\\u003e39\\u003c/b\\u003e, e1\\u0026ndash;e9 (2011).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eLindsley, W. 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Pulsed Broad-Spectrum UV Light Effectively Inactivates SARS-CoV-2 on Multiple Surfaces and N95 Material. \\u003cem\\u003eViruses.\\u003c/em\\u003e \\u003cb\\u003e13\\u003c/b\\u003e, 460 (2021).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eRaeiszadeh, M. \\u0026amp; Adeli, B. A. Critical Review on Ultraviolet Disinfection Systems against COVID-19 Outbreak: Applicability, Validation, and Safety Considerations. \\u003cem\\u003eACS Photonics.\\u003c/em\\u003e \\u003cb\\u003e7\\u003c/b\\u003e, 2941\\u0026ndash;2951 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eGolladay, G. J. \\u003cem\\u003eet al.\\u003c/em\\u003e Rationale and process for N95 respirator sanitation and re-use in the COVID-19 pandemic. \\u003cem\\u003eInfect. Control Hosp. 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Sci.\\u003c/em\\u003e \\u003cb\\u003e19\\u003c/b\\u003e, 746\\u0026ndash;751 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eWharton, K. \\u0026amp; Rieker, M. N95 Respirator Decontamination and Reuse: Current State of the Evidence.\\u003cem\\u003eAANA Journal\\u003c/em\\u003e6 (2020).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eHeimbuch, B. \\u0026amp; Harnish, D. Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies(2019).\\u003c/span\\u003e\\u003c/li\\u003e \\u003cli\\u003e\\u003cspan\\u003eTcharkhtchi, A. \\u003cem\\u003eet al.\\u003c/em\\u003e An overview of filtration efficiency through the masks: Mechanisms of the aerosols penetration. \\u003cem\\u003eBioactive Materials.\\u003c/em\\u003e \\u003cb\\u003e6\\u003c/b\\u003e, 106\\u0026ndash;122 (2021).\\u003c/span\\u003e\\u003c/li\\u003e\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":true,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"scientific-reports\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"scirep\",\"sideBox\":\"Learn more about [Scientific Reports](http://www.nature.com/srep/)\",\"snPcode\":\"\",\"submissionUrl\":\"\",\"title\":\"Scientific Reports\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Scientific Reports\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":true},\"keywords\":\"personal protective equipment (PPE), N95 filter facepiece respirators (FFR), Fourier-transform infrared (FTIR, PET-P bands\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-435322/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-435322/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eThe recent surge in the use of UV technology for personal protective equipment (PPE) has created a unique learning opportunity for the UV industry to deepen surface disinfection knowledge, especially on surfaces with complex geometries, such as the N95 filter facepiece respirators (FFR). The work outlined in this study addresses the interconnectedness of independent variables (e.g., UV Fluence, respirator material) that require consideration when assessing UV light efficacy for disinfecting respirators. Through electron microscopy and Fourier-transform infrared (FTIR) spectroscopy, we characterized respirator filter layers and revealed that polymer type affects disinfection efficacy. Specifically, FFR layers made from polypropylene (PP) (hydrophobic in nature) resulted in higher disinfection efficiency than layers composed of polyethylene terephthalate (PET-P) (hygroscopic in nature). An analysis of elastic band materials on the respirators indicated that silicone rubber-based bands achieved higher disinfection efficiency than PET-P bands and have a woven, fabric-like texture. While there is a strong desire to repurpose respirators, through this work we demonstrated that the design of an appropriate UV system is essential and that only respirators meeting specific design criteria may be reasonable for repurposing via UV disinfection.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Specificity of UV-C LED Disinfection Efficacy for Three N95 Respirators\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2021-04-30 19:25:46\",\"doi\":\"10.21203/rs.3.rs-435322/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"decision\",\"content\":\"Major revision\",\"date\":\"2021-06-11T04:28:40+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2021-06-02T13:13:44+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"db777f98-66e4-4a44-8d25-3cf7571db459\",\"date\":\"2021-06-02T10:56:23+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"40aa00b7-34ee-4798-9495-33fb3ca7146e\",\"date\":\"2021-05-30T17:24:23+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2021-05-27T10:08:30+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2021-05-27T10:02:40+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvited\",\"content\":\"\",\"date\":\"2021-04-28T13:15:49+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"checksComplete\",\"content\":\"\",\"date\":\"2021-04-28T11:48:26+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Scientific Reports\",\"date\":\"2021-04-17T17:55:24+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"scientific-reports\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"scirep\",\"sideBox\":\"Learn more about [Scientific Reports](http://www.nature.com/srep/)\",\"snPcode\":\"\",\"submissionUrl\":\"\",\"title\":\"Scientific Reports\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Scientific Reports\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"ff91fb55-de22-495c-84e9-dd0942105407\",\"owner\":[],\"postedDate\":\"April 30th, 2021\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"published-in-journal\",\"subjectAreas\":[{\"id\":3985460,\"name\":\"Materials Engineering\"},{\"id\":3985461,\"name\":\"General Microbiology\"},{\"id\":3985462,\"name\":\"Photonics/optics\"}],\"tags\":[],\"updatedAt\":\"2021-08-22T15:19:32+00:00\",\"versionOfRecord\":{\"articleIdentity\":\"rs-435322\",\"link\":\"https://doi.org/10.1038/s41598-021-94810-4\",\"journal\":{\"identity\":\"scientific-reports\",\"isVorOnly\":false,\"title\":\"Scientific Reports\"},\"publishedOn\":\"2021-07-28 15:04:53\",\"publishedOnDateReadable\":\"July 28th, 2021\"},\"versionCreatedAt\":\"2021-04-30 19:25:46\",\"video\":\"\",\"vorDoi\":\"10.1038/s41598-021-94810-4\",\"vorDoiUrl\":\"https://doi.org/10.1038/s41598-021-94810-4\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-435322\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-435322\",\"identity\":\"rs-435322\",\"version\":[\"v1\"]},\"buildId\":\"J0_U0BvcaRcwD8yVFaRlm\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}