LitCovid-sentences  

PMC:7796291 / 1598-27726 JSONTXT 3 Projects

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Id Subject Object Predicate Lexical cue
T11 0-2 Sentence denotes 1.
T12 3-15 Sentence denotes Introduction
T13 16-183 Sentence denotes The demand for face filtering respirators has grown continuously to cope with various environmental hazards including fine dust, liquid mist, bioaerosol, and droplets.
T14 184-257 Sentence denotes In the meantime, the outbreak of COVID-19 has sculpted a new way of life.
T15 258-526 Sentence denotes Since pathogens can be transmitted via bioaerosol or droplets generated by coughing or sneezing, the use of respirators is now an everyday necessity as the front-line safety tool to protect both the wearer and others from the exposure to such infectious matters [1,2].
T16 527-654 Sentence denotes According to the Institute of Medicine (IOM), a six-week influenza pandemic results in a demand for 90 million respirators [3].
T17 655-915 Sentence denotes Likewise, the prevalence of the COVID-19 pandemic has led to a worldwide shortage of respirators, and this situation resulted in the undiscerning reuse of disposable respirators, although most users are not informed of proper methods of respirator maintenance.
T18 916-1198 Sentence denotes While little information is available with respect to standardized cleaning methods, commonly used methods to disinfect the used respirators include ultraviolet (UV) irradiation, microwaving, sunlight exposure, laundering, ethanol-spray, heating with a hairdryer, and ironing [4,5].
T19 1199-1380 Sentence denotes However, there is a lack of scientific evidence on whether such treatments are indeed effective and safe in disinfecting biological matter and preserving filtration performance [6].
T20 1381-1506 Sentence denotes Therefore, it is imperative to investigate the validity and effectiveness of disinfection methods for disposable respirators.
T21 1507-1919 Sentence denotes As a contingency strategy for the capacity crisis of disposable respirators, the Centers for Disease Control and Prevention and the National Institute of Occupational Safety and Health announced the guidelines of potential disinfection methods for the reuse of disposable respirators, which include the application of ultraviolet (UV) germicidal irradiation, vaporous hydrogen peroxide (VHP), and moist heat [5].
T22 1920-2054 Sentence denotes Table 1 shows the summary of previous studies on respirator disinfection methods [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24].
T23 2055-2263 Sentence denotes As for the bactericidal efficiency, autoclaving, UV irradiation, and chemical solvent treatments using bleach, ethanol, and VHP showed up to a 99% reduction of tested bacteria or virus [21,25,26,27,28,29,30].
T24 2264-2380 Sentence denotes Nevertheless, some of the results lacked the coherence, and not every method was tested for the bactericidal effect.
T25 2381-2537 Sentence denotes Thus, a comprehensive investigation is called for to understand the effect of disinfection methods on filtration performance and bactericidal effectiveness.
T26 2538-2677 Sentence denotes The particle filtration of an electret media is attributed to the mechanical capture and the electrostatic attraction of particles [31,32].
T27 2678-2909 Sentence denotes Many previous studies associated the deteriorated performance of disinfection-treated respirators with the loss of electrostatic charges [7,9,11,15,17,18,19,22,25], yet the direct evidence of charge deterioration was often missing.
T28 2910-3076 Sentence denotes Additionally, it has hardly been examined for the effect of treatment on the structural integrity of the filter media, which may affect the resistance of respirators.
T29 3077-3247 Sentence denotes This study aims at divulging the effects of disinfection treatments on inactivation/removal of bacteria, deterioration of filtration performance and structural integrity.
T30 3248-3519 Sentence denotes To this end, commonly-applied disinfection methods were employed as reuse treatments of respirators, which included microwaving, oven-dry, UV irradiation, immersions in hypochlorite (ClO−), ethanol (EtOH), and isopropanol (IPA), and laundering with and without detergent.
T31 3520-3722 Sentence denotes The influence of disinfection treatment on bactericidal effect was investigated using Escherichia coli (E. coli) bacteria, as a common Gram-negative bacteria with viability in diverse environments [33].
T32 3723-3930 Sentence denotes The change of filtration performance after treatments and the probable causes for the change were examined by measuring surface potential, wettability, chemical property, and the morphology of filter fibers.
T33 3931-4166 Sentence denotes The approach of this study is significant in that the validity of various disinfection methods were extensively investigated, associating the deteriorated performance with the physicochemical changes of electret media after treatments.
T34 4167-4286 Sentence denotes Rarely has it been conducted for this level of inclusive investigation to reveal the impact of disinfection treatments.
T35 4287-4466 Sentence denotes This study intends to provide practical yet fundamental information on the effect of disinfection treatments in multifarious aspects including bactericidal and filter performance.
T36 4468-4470 Sentence denotes 2.
T37 4471-4492 Sentence denotes Materials and Methods
T38 4494-4498 Sentence denotes 2.1.
T39 4499-4510 Sentence denotes Respirators
T40 4511-4573 Sentence denotes A commercial respirator certified by N95 grade (coded as Resp.
T41 4574-4674 Sentence denotes A) and the one certified by the Korean Ministry of Food and Drug Safety (MFDS) for KF94 grade (Resp.
T42 4675-4710 Sentence denotes B) were used as sample respirators.
T43 4711-4906 Sentence denotes N95 and KF94 grades refer to the particle capture efficiency of not less than 95% during 200 mg of NaCl particle loading [34] and 94% after 3 min NaCl and paraffin oil loading [35], respectively.
T44 4907-4932 Sentence denotes The surface area of Resp.
T45 4933-4944 Sentence denotes A and Resp.
T46 4945-4986 Sentence denotes B were 249 cm2 and 208 cm2, respectively.
T47 4988-4992 Sentence denotes 2.2.
T48 4993-5016 Sentence denotes Disinfection Treatments
T49 5018-5024 Sentence denotes 2.2.1.
T50 5025-5046 Sentence denotes Microwave Irradiation
T51 5047-5335 Sentence denotes Metal nose clips of respirators were eliminated, and the respirators were exposed to microwave irradiation with 750 W power (MR-280M, LG Electronics, Seoul, Korea); for 1 min, the outer side was directed to the irradiation, then, for 1 min, the inner side was directed to the irradiation.
T52 5336-5430 Sentence denotes All treated samples were stored for 12 h under ambient temperature before the filtration test.
T53 5432-5438 Sentence denotes 2.2.2.
T54 5439-5447 Sentence denotes Oven-Dry
T55 5448-5545 Sentence denotes Respirators were dried at 90 °C for 1 h in a drying oven (Withlab Co., Ltd., Gyeonggi-do, Korea).
T56 5547-5553 Sentence denotes 2.2.3.
T57 5554-5568 Sentence denotes UV Irradiation
T58 5569-5681 Sentence denotes UV rays were radiated from 16.5 cm away from the tray using a UV sterilizer (KRS-A1, KARIS, Gyeonggi-do, Korea).
T59 5682-5797 Sentence denotes The wavelength of 253.7 nm UV ray was irradiated through the inner area of the sterilizer in 42 cm × 32 cm × 32 cm.
T60 5798-5949 Sentence denotes The power consumption of UV light bulb was 10 W and the irradiation was conducted for 1 h for inner side and another 1 h for outer side of respirators.
T61 5951-5957 Sentence denotes 2.2.4.
T62 5958-5992 Sentence denotes Chlorinated Disinfectant Immersion
T63 5993-6179 Sentence denotes Chlorine-based disinfectant (Yuhan Corporation, Seoul, Korea), formulated with sodium hypochlorite (NaClO) (5.5%), sodium hydroxide (NaOH) (0.3%), and water, was used for this treatment.
T64 6180-6322 Sentence denotes The chlorine disinfectant was diluted in tap water to 5% (v/v), which makes the final sodium hypochlorite concentration in water to be 0.275%.
T65 6323-6478 Sentence denotes The respirator samples were soaked in the solution for 10 min, then rinsed in tap water for 3 min two times, and dried for 24 h under an ambient condition.
T66 6480-6486 Sentence denotes 2.2.5.
T67 6487-6504 Sentence denotes Ethanol Immersion
T68 6505-6630 Sentence denotes The respirator samples were immersed in an aq. ethanol (EtOH) solution of 70% (v/v) for 10 min, then dried for at least 24 h.
T69 6632-6638 Sentence denotes 2.2.6.
T70 6639-6660 Sentence denotes Isopropanol Immersion
T71 6661-6744 Sentence denotes Isopropanol (IPA) is commonly known as a discharging agent for electret media [36].
T72 6745-6816 Sentence denotes Respirators were immersed in IPA liquid (≥99.9%) for 10 min, and dried.
T73 6818-6824 Sentence denotes 2.2.7.
T74 6825-6835 Sentence denotes Laundering
T75 6836-6898 Sentence denotes Laundering of respirators was done with and without detergent.
T76 6899-7069 Sentence denotes For water-laundering without detergent, each respirator was put in a stainless can of Terg-O-Tometer (T-O-T, Yasuda Seiki Seisakusho, Tokyo, Japan) with 1 L of tap water.
T77 7070-7216 Sentence denotes The laundering with water (without detergent) was conducted with agitation speed of 90 rpm at 24 °C for 10 min, and then 3 min for two more times.
T78 7217-7334 Sentence denotes For detergent-laundering, a detergent (Actz power gel, Pigeon, Seoul, Korea) composed of anionic surfactant was used.
T79 7335-7566 Sentence denotes Respirators were laundered in T-O-T with 1 L of 0.1 wt% aq. detergent solution at 24 °C and 90 rpm for 10 min, then the samples were rinsed with 1 L of tap water for 3 min four times to thoroughly remove the detergent residue [37].
T80 7568-7572 Sentence denotes 2.3.
T81 7573-7604 Sentence denotes Electrostatic Force Measurement
T82 7605-7767 Sentence denotes The surface potential of filter media was measured using an electrostatic voltmeter (Model 542A, Trek, Lockport, NY, USA), by holding the filter media in the air.
T83 7768-7903 Sentence denotes A charge-monitoring probe was placed 4 cm above the web surface, and the surface potential was measured by line-scanning over the area.
T84 7905-7909 Sentence denotes 2.4.
T85 7910-7925 Sentence denotes Filtration Test
T86 7926-8188 Sentence denotes The filtration performance of respirators was evaluated using an automated filter tester (TSI 8130, TSI Inc., Shoreview, MN, USA), using NaCl particles (mass median diameter, MMD ~0.6 µm) and paraffin oil aerosol (MMD ~0.4 µm), based on the Korean MFDS standard.
T87 8189-8377 Sentence denotes NaCl aerosol with a mass concentration of 8 ± 4 mg/m3 or paraffin oil aerosol with a mass concentration of 20 ± 5 mg/m3 was passed through the respirator sample at the flow rate of 95 LPM.
T88 8378-8506 Sentence denotes The aerosol penetration after 3 min of challenged aerosol mass and the initial resistance were recorded as performance criteria.
T89 8508-8512 Sentence denotes 2.5.
T90 8513-8529 Sentence denotes Characterization
T91 8530-8762 Sentence denotes For a non-destructive 3D visualizations of an internal structure of materials, X-ray computed tomography (Xµ-CT) was performed using Zeiss X-Radia 510 Versa (Zeiss, Oberkochen, Germany) (Figure S1, see Supplementary Materials) [38].
T92 8763-8837 Sentence denotes The X-ray source was operated at a voltage of 60 kV with a power of 5.0 W.
T93 8838-8957 Sentence denotes The fields of view used were 800, 1200, 2000 µm, and the corresponding pixel sizes were 0.8, 1.2, 2.0 µm, respectively.
T94 8958-9170 Sentence denotes FE-SEM images of filter samples were observed by Supra 55 VP (Zeiss, Oberkochen, Germany), with prior coating with Pt at 20 mA for 120 s, using a 108auto sputter coater (Cressington Scientific Inc., Watford, UK).
T95 9171-9271 Sentence denotes The thickness of respirator layers was measured using a thickness gauge under the pressure of 2.4 N.
T96 9272-9552 Sentence denotes Porosity and solidity of webs were calculated based on Equations (1) and (2), where m is mass of the material, A is area of the material, t is thickness, and ρ is the material density (0.95 g/cm3 for PP was used):Porosity (%) = (1 − solidity) × 100 (%)(1) Solidity = m/(A⋅t⋅ρ)(2)
T97 9553-9709 Sentence denotes The static contact angle (CA) of liquid was gauged as wetting property using a contact angle analyzer (SmartDrop Lab, FemtoBiomed Inc., Gyeonggi-do, Korea).
T98 9710-9967 Sentence denotes A droplet of 3.0 ± 0.3 μL liquid, including distilled water (WA), ethanol (EtOH), isopropanol (IPA), chlorinated disinfectant (ClO−), and 0.1% detergent solution was dispensed on a surface of web, and CA was measured in 60 s after the droplets were settled.
T99 9968-10053 Sentence denotes The chemistry of sample surface was analyzed by FTIR-ATR (TENSOR27, Bruker, Germany).
T100 10055-10059 Sentence denotes 2.6.
T101 10060-10079 Sentence denotes Bactericidal Effect
T102 10080-10237 Sentence denotes The E. coli strain of KCTC 1039 was used as the test bacteria, cultivated in Luria-Bertani (LB) broth (Sigma-Aldrich, St. Louis, MO, USA) for 2 h at 250 rpm.
T103 10238-10494 Sentence denotes For application of E. coli to respirator layers, 10 μL of bacterial culture, corresponding to ~5 × 106 CFU of E. coli (concentration; 5 × 108 CFU/mL), was injected into the center area of 2.5 cm × 2.5 cm of front side of a respirator, using a micropipette.
T104 10495-10645 Sentence denotes The bacteria-loaded samples were subject to different disinfection treatments, and the CFUs of cells were quantified, using a staining method [39,40].
T105 10646-10703 Sentence denotes The quantification procedure is illustrated in Figure S2.
T106 10705-10707 Sentence denotes 3.
T107 10708-10730 Sentence denotes Results and Discussion
T108 10731-10850 Sentence denotes The influence of various disinfection methods on the filtration and bactericidal performance was investigated for Resp.
T109 10851-10862 Sentence denotes A and Resp.
T110 10863-10865 Sentence denotes B.
T111 10866-10991 Sentence denotes The 3D images of layer constructions for those respirators were analyzed by the X-ray computed tomography (Xμ-CT) (Figure 1).
T112 10992-11171 Sentence denotes Common components of respirators included: a spunbond coverweb, one or two layers of electrostatically charged meltblown filter webs, and a spunbond inner web. respirator A (Resp.
T113 11172-11238 Sentence denotes A) had an additional stiffener web and 2 layers of meltblown webs.
T114 11239-11332 Sentence denotes The meltblown filter web was comprised of very thin fibers <2.5 μm in a considerable portion.
T115 11333-11365 Sentence denotes In contrast, respirator B (Resp.
T116 11366-11462 Sentence denotes B) consisted of a single layer filter web of which fiber diameter ranged from 2.5 μm to 12.5 μm.
T117 11463-11618 Sentence denotes The thickness of each layer of the respirators was measured firsthand with a thickness gauge applying a pressure of 2.4 N, and is presented in Figure 1C,F.
T118 11619-11744 Sentence denotes It is noted that the measurements by the gauge were smaller than those estimated from the specific locations of Xμ-CT images.
T119 11745-11843 Sentence denotes When analyzing the morphological changes in the later sections, first-hand measurements were used.
T120 11845-11849 Sentence denotes 3.1.
T121 11850-11908 Sentence denotes Filtration Performance with Varied Disinfection Treatments
T122 11909-12032 Sentence denotes Varied disinfection methods accessible to the general public were investigated for their effects on filtration performance.
T123 12033-12132 Sentence denotes Without disinfection treatments, both respirators showed very high filtration efficiency of ≥99.5%.
T124 12133-12348 Sentence denotes It should be noted that the filtration efficiency was measured after challenging the respective aerosols for 3 min (by the KF standard) [35], which corresponded to about 2.7 mg of NaCl and 8 mg of paraffin oil mass.
T125 12349-12531 Sentence denotes The filtration performance against NaCl and paraffin oil aerosols were comparable, and the effects of various treatments on filtration of either aerosol were very similar (Figure 2).
T126 12532-12688 Sentence denotes The resistances of respirators were mostly consistent regardless of treatments, except that laundering treatments slightly decreased the resistance of Resp.
T127 12689-12691 Sentence denotes A.
T128 12692-12807 Sentence denotes The physical characteristics of respirators before and after treatment were further investigated in later sections.
T129 12808-12969 Sentence denotes As for the filtration efficiency, the organic solvents such as IPA and EtOH, and detergent-laundering deteriorated the filtration efficiency of both respirators.
T130 12970-13063 Sentence denotes Particularly for IPA and EtOH treatments, up to ~28% of efficiency was lost after treatments.
T131 13064-13326 Sentence denotes Considering that the resistance of the solvent-treated samples was unchanged, it can be inferred that the solvents caused the reduction of filtration performance by affecting the electrostatic filtration capacity, rather than disrupting the structural integrity.
T132 13327-13416 Sentence denotes Similarly, the filtration efficiency was notably reduced after laundering with detergent.
T133 13417-13609 Sentence denotes As laundering with water barely affected the filtration efficiency, this indicates that the detergent negatively affected it, probably through an impact on the electrostatic capture mechanism.
T134 13610-13756 Sentence denotes Physical treatments employing UV irradiation, oven-dry, and microwave irradiation caused little impact on the filtration efficiency or resistance.
T135 13757-14014 Sentence denotes Previous studies reported the deteriorated performance with thermal treatment of electret filters [10,41], but most of the performance deterioration occurred with harsher conditions (120 °C, 48 h) and especially for materials with high dielectric constants.
T136 14015-14212 Sentence denotes Aging the electret filter at an extremely high temperature can trigger the mobility of polymer chains and charge carriers, leading to the loss of charges and increased particulate penetration [41].
T137 14213-14451 Sentence denotes In this study, the polypropylene electret filters were treated by the oven-dry condition that was relatively mild and short-term (90 °C, 1 h); and for this reason, the oven-dry treatment caused negligible effect on the performance change.
T138 14452-14697 Sentence denotes UV irradiation may influence the performance by causing the surface oxidation, turning the surface hydrophilic [42]; and the increased conductivity in a humid condition can lead to the loss of charges, reducing the filtration efficiency [43,44].
T139 14698-14845 Sentence denotes However, UV irradiation, at the level of 10 W power with 253.7 nm wavelength, of this study did not significantly affect the filtration efficiency.
T140 14846-15076 Sentence denotes The results in Figure 2 show that thermal (oven-dry and microwave) and UV treatments hardly affected the filtration performance, aside from the fact that microwaving is not recommended for the safety reasons with metal components.
T141 15077-15155 Sentence denotes Samples laundered with water maintained the performance as the untreated ones.
T142 15156-15274 Sentence denotes However, the probable structural change, the torn coverweb (Figure S3), during the laundering procedure is of concern.
T143 15275-15398 Sentence denotes Thickness and porosity of filter webs after treatments showed little differences compared to the untreated webs (Table S1).
T144 15399-15519 Sentence denotes The residues on fibers after detergent-laundering is also of concern in the regard of environmental impacts (Figure S5).
T145 15521-15525 Sentence denotes 3.2.
T146 15526-15538 Sentence denotes Charge Decay
T147 15539-15662 Sentence denotes To examine the cause of reduced performance, the surface potential of the filter web was measured (Figure 3 and Figure S6).
T148 15663-15876 Sentence denotes The surface charges of the filter media are not consistently positive or negative; instead, both positive and negative charges can exist simultaneously, compensating the overall charges on the filter surface [45].
T149 15877-16002 Sentence denotes Therefore, for such cases, the average surface potential over an area can be less meaningful than the variation of potential.
T150 16003-16177 Sentence denotes In Figure 3, the surface potential across the horizontal line was measured by line-scanning, and the fluctuation of the voltage values was observed as an important parameter.
T151 16178-16404 Sentence denotes The surface potential of the untreated filter webs from respirators A and B ranged from −1.6 kV to +4.4 kV, and these surface charges contributed to particle capture either by coulombic attraction or induced polarization [46].
T152 16405-16535 Sentence denotes When the electret media was exposed to IPA, EtOH, and detergent solution, the range of surface potential was considerably reduced.
T153 16536-16674 Sentence denotes In particular, IPA-treated respirator exhibited nearly 0 kV invariably across all areas, clearly indicating the loss of surface potential.
T154 16675-16858 Sentence denotes The EtOH or detergent-treated respirators showed a slightly larger variation than the IPA-treated ones, indicating that surface charges may not be completely lost by those treatments.
T155 16859-17080 Sentence denotes The remaining charges would contribute to electrostatic filtration mechanism, as indicated by the higher filtration efficiency of EtOH and detergent-treated respirators compared to that of the IPA-treated ones (Figure 2).
T156 17081-17255 Sentence denotes The charge decay occurred by the exposure to alcohol and detergent solution was probably due to the mobility of the charge carrier caused by the penetration of liquid [9,24].
T157 17256-17403 Sentence denotes Water has high surface tension and does not wet the polypropylene (PP) surface; therefore, the effect of water-immersion on PP media is negligible.
T158 17404-17632 Sentence denotes IPA and EtOH immediately wetted the PP media in each layer as represented by the contact angle ~0° (Figure 4); and penetration of solvents into PP molecules expedited the charge carrier mobility, quickly dissipating the charges.
T159 17633-17785 Sentence denotes In the case of 0.1% detergent solution, instantaneous contact angle was around 120°, then within 30~60 s, the PP web fully absorbed the liquid droplets.
T160 17786-17969 Sentence denotes As the affinity of detergent solution to PP was not as high as EtOH or IPA, the impact of detergent on the electrostatic filtration was not as significant as that of organic solvents.
T161 17970-18137 Sentence denotes Unlike the other test liquid, the ClO− droplet maintained the contact angle of 140° without spreading, and the electrostatic filtration was hardly affected (Figure 2).
T162 18138-18408 Sentence denotes Among the treatments, detergent treatment reduced the contact angle; this increased surface wettability of filter web would adversely influence the charge retention by increasing the electric conductivity, as evidenced from the surface potential measurement in Figure 3.
T163 18409-18508 Sentence denotes As a result, the filtration performance after detergent treatment significantly decreased (≥10.8%).
T164 18509-18679 Sentence denotes To examine whether UV-treated or detergent-laundered respirators changed their chemistry, contact angles and FTIR spectra from those surfaces were examined (Figure 4B,C).
T165 18680-18852 Sentence denotes Untreated PP media has C-H stretching (2906 cm−1), CH2/CH3 asymmetrical bending (around 2982 cm−1), and other carbon and hydrogen bonding (2835 to 2972 cm−1) peaks [47,48].
T166 18853-18980 Sentence denotes After UV irradiation, distinctive peaks were observed for: C-O-C (around 1058 cm−1) and O-H bending (around 1161 cm−1) [49,50].
T167 18981-19135 Sentence denotes The changed surface chemistry seemed to attribute to surface oxidation, but hardly affected the wettability and filtration performance after UV treatment.
T168 19136-19248 Sentence denotes Solvent treatments with IPA, EtOH, and ClO− showed neither noxious residues nor distinctive hydrophilic bonding.
T169 19250-19254 Sentence denotes 3.3.
T170 19255-19276 Sentence denotes Mechanical Filtration
T171 19277-19391 Sentence denotes The particle capture of an electret filter is contributed by both mechanical and electrostatic capture mechanisms.
T172 19392-19624 Sentence denotes An electrostatic capture mechanism significantly improves the quality factor (filtration performance per a unit resistance); and when the surface charges are decayed, filtration mostly depends on the mechanical capture of particles.
T173 19625-19858 Sentence denotes It is well accepted that IPA treatment removes the surface charges of filter media; therefore, the IPA-treated samples can be deemed as the mechanical filter (mechanical contribution noted as “mech. cont’n”) (Figure 2 and Figure 3B).
T174 19859-20014 Sentence denotes The performance above this level of filtration for the untreated respirators A and B is considered as the electrostatic capture mechanism (electr. cont’n).
T175 20015-20290 Sentence denotes Disinfection treatments such as solvent immersion, UV, oven-dry, and microwaving seemed to have negligible impacts on the structural integrity (Figures S3 and S4); accordingly, there were no apparent changes in the resistance and mechanical filtration after those treatments.
T176 20291-20408 Sentence denotes Notable fiber damage was found in the laundered samples by the external force imposed during laundering (Figure S3A).
T177 20409-20437 Sentence denotes The physical damage of Resp.
T178 20438-20586 Sentence denotes A resulted in the decrease of resistance and mechanical filtration performance, corresponding to the lower filtration efficiency compared with Resp.
T179 20587-20589 Sentence denotes B.
T180 20591-20595 Sentence denotes 3.4.
T181 20596-20647 Sentence denotes Bactericidal Performance of Disinfection Treatments
T182 20648-20780 Sentence denotes To investigate the disinfection efficacy, the number of survived colony on respirators after disinfection treatments was quantified.
T183 20781-20963 Sentence denotes The E. coli culture was loaded on the respirators applying physical pressure; the bacteria culture penetrated up to the stiffener, and did not penetrate beyond this layer (Figure 5).
T184 20964-21060 Sentence denotes Without the physical pressure, the loaded culture drop rolled around on the surface of coverweb.
T185 21061-21185 Sentence denotes The number of loaded E. coli by each layer was correlated with OD470 measurement and expressed as CFU/cm2 substrate surface.
T186 21186-21467 Sentence denotes Bacteria inactivation or removal efficiency was calculated by: (B0−Bn)B×100 (%), where B0 is the number of live bacteria in the untreated sample area, and Bn is the number of live bacteria in the treated sample area (n = 1~8, each number indicating the eight disinfection methods).
T187 21468-21520 Sentence denotes Bactericidal or bacteria removal efficiency of Resp.
T188 21521-21558 Sentence denotes A is shown in Figure 6 and Figure S7.
T189 21559-21715 Sentence denotes In the 2.5 cm × 2.5 cm designated area of each web, non-treated samples showed ~1.46 × 106 and ~2.53 × 106 CFUs on the coverweb and stiffener, respectively.
T190 21716-21919 Sentence denotes Microwaving, oven-dry, and UV treatment showed similar bactericidal effect up to about 82%; in fact, this is inconsistent with previous studies [18,20], where 99.99% inactivation efficiency was achieved.
T191 21920-22071 Sentence denotes This discrepancy can be attributed to the different treatment conditions, such as irradiation intensity, treatment time, and amount of bacteria loaded.
T192 22072-22297 Sentence denotes In a previous study, 1.0 × 106 CFU of bacteria was loaded on the respirator with a nebulizer; and the UV irradiation (wavelength; 254 nm, 5 min) and microwaving (400 W, 10 min) resulted in complete inactivation of cells [18].
T193 22298-22478 Sentence denotes The case of an oven-dry treatment (100 °C, 15 min) also achieved 99.99% inactivation efficiency, when 5.0 × 104 CFU of bacteria was dropped onto the surface of the respirator [20].
T194 22479-22609 Sentence denotes Compared to previous studies, this study built a harsher experimental condition with a higher loading of bacteria (5.0 × 106 CFU).
T195 22610-22802 Sentence denotes As a result, the intensity of microwaving (750 W, 2 min), UV irradiation (wavelength; 253.7 nm, 2 h), and oven-dry (90 °C, 1 h) of this study were insufficient for complete sterilization [51].
T196 22803-22997 Sentence denotes Chemical solvents (ClO−, EtOH, and IPA) and laundering treatments showed no color change with cell staining, indicating 100% bactericidal or bacteria removal efficiency (Figure 6 and Figure S7).
T197 22998-23106 Sentence denotes The morphological state of loaded bacteria after disinfection treatments was analyzed by FE-SEM (Figure 6C).
T198 23107-23316 Sentence denotes With microwaving, oven-dry, and UV irradiation, disruption of E. coli membrane integrity was observed; on the contrary, IPA immersion and water-laundering resulted in both cell deformation and cell detachment.
T199 23317-23445 Sentence denotes Remaining bacteria on water-laundered media was observed in a tangled structure of cells with contaminants on the fiber surface.
T200 23446-23613 Sentence denotes Generally, microwaving and oven-drying rely solely on the heating effect to inactivate microorganisms [52], as heating triggers the denaturation of cell proteins [53].
T201 23614-23782 Sentence denotes Additionally, the UV irradiation breaks the strong bond of cell membranes, such as O-H, P-O, and N-H bonds of E. coli, or induces oxidation, leading to cell death [54].
T202 23783-24049 Sentence denotes The solvents and detergent laundering treatments have compound effect of bactericidal and bacteria removal activity, by accumulating in the lipid of membrane and degrading the membrane integrity while inducing suspension of bacterial droplet into the liquid [55,56].
T203 24050-24166 Sentence denotes Meanwhile, laundering effectively removed bacteria by detaching them from fibers, rather than sterilizing the cells.
T204 24167-24362 Sentence denotes The results of bactericidal performance test imply the chemical solvents and hypochlorite solution are effective disinfection agents, as they concurrently inactivate the cell and detach bacteria.
T205 24363-24503 Sentence denotes Even if it is not complete sterilization, UV irradiation, and oven-dry methods seem fairly applicable for inactivating cells to some extent.
T206 24504-24633 Sentence denotes Laundering treatment removed a considerable amount of loaded bacteria; additionally, even the remaining bacteria was inactivated.
T207 24635-24637 Sentence denotes 4.
T208 24638-24649 Sentence denotes Conclusions
T209 24650-24792 Sentence denotes For the environmental protection during a global pandemic under the supply shortage, the reusability of disposable respirators was inevitable.
T210 24793-25020 Sentence denotes This study evaluated the effects of varied disinfection treatments of disposable respirators on the filtration performance, morphological integrity, and bactericidal effectiveness, adopting eight different disinfection methods.
T211 25021-25327 Sentence denotes It was confirmed that disinfection methods including laundering and chemical treatments effectively reduced the risk of bacterial infection via inactivating or removing adhered bacteria; however, they significantly deteriorated the filtration performance, dissipating the electrostatic force of the fibers.
T212 25328-25457 Sentence denotes The oven-dry and UV irradiation maintained the performance, but showed incomplete sterilization in a harsh microbial environment.
T213 25458-25650 Sentence denotes The results of this study will ultimately contribute to the advancement of environmental health and safety by providing a scientific background on the effect of disinfection treatment methods.
T214 25651-25801 Sentence denotes Further investigation simulating the actual pandemic environment is recommended to identify the effective methods in the varied infectious conditions.
T215 25802-26029 Sentence denotes Additionally, a potential risk of secondary infection by the released active bacteria back to the environment needs to be further investigated, to suggest the most relevant disinfection method for public health and environment.
T216 26030-26087 Sentence denotes The scope of this study remains in bacteria disinfection.
T217 26088-26128 Sentence denotes Further study with virus is recommended.