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{"project":"LitCovid-PD-HP","denotations":[{"id":"T2","span":{"begin":2667,"end":2676},"obj":"Phenotype"}],"attributes":[{"id":"A2","pred":"hp_id","subj":"T2","obj":"http://purl.obolibrary.org/obo/HP_0000713"}],"text":"2. Materials and Methods\n\n2.1. Respirators\nA commercial respirator certified by N95 grade (coded as Resp. A) and the one certified by the Korean Ministry of Food and Drug Safety (MFDS) for KF94 grade (Resp. B) were used as sample respirators. 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. The surface area of Resp. A and Resp. B were 249 cm2 and 208 cm2, respectively.\n\n2.2. Disinfection Treatments\n\n2.2.1. Microwave Irradiation\nMetal 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. All treated samples were stored for 12 h under ambient temperature before the filtration test.\n\n2.2.2. Oven-Dry\nRespirators were dried at 90 °C for 1 h in a drying oven (Withlab Co., Ltd., Gyeonggi-do, Korea).\n\n2.2.3. UV Irradiation\nUV rays were radiated from 16.5 cm away from the tray using a UV sterilizer (KRS-A1, KARIS, Gyeonggi-do, Korea). The wavelength of 253.7 nm UV ray was irradiated through the inner area of the sterilizer in 42 cm × 32 cm × 32 cm. 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.\n\n2.2.4. Chlorinated Disinfectant Immersion\nChlorine-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. 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%. 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.\n\n2.2.5. Ethanol Immersion\nThe respirator samples were immersed in an aq. ethanol (EtOH) solution of 70% (v/v) for 10 min, then dried for at least 24 h.\n\n2.2.6. Isopropanol Immersion\nIsopropanol (IPA) is commonly known as a discharging agent for electret media [36]. Respirators were immersed in IPA liquid (≥99.9%) for 10 min, and dried.\n\n2.2.7. Laundering\nLaundering of respirators was done with and without detergent. 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. 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. For detergent-laundering, a detergent (Actz power gel, Pigeon, Seoul, Korea) composed of anionic surfactant was used. 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].\n\n2.3. Electrostatic Force Measurement\nThe 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. A charge-monitoring probe was placed 4 cm above the web surface, and the surface potential was measured by line-scanning over the area.\n\n2.4. Filtration Test\nThe 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. 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. The aerosol penetration after 3 min of challenged aerosol mass and the initial resistance were recorded as performance criteria.\n\n2.5. Characterization\nFor 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]. The X-ray source was operated at a voltage of 60 kV with a power of 5.0 W. The fields of view used were 800, 1200, 2000 µm, and the corresponding pixel sizes were 0.8, 1.2, 2.0 µm, respectively.\nFE-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). The thickness of respirator layers was measured using a thickness gauge under the pressure of 2.4 N. 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)\nThe static contact angle (CA) of liquid was gauged as wetting property using a contact angle analyzer (SmartDrop Lab, FemtoBiomed Inc., Gyeonggi-do, Korea). 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. The chemistry of sample surface was analyzed by FTIR-ATR (TENSOR27, Bruker, Germany).\n\n2.6. Bactericidal Effect\nThe 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. 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. The bacteria-loaded samples were subject to different disinfection treatments, and the CFUs of cells were quantified, using a staining method [39,40]. The quantification procedure is illustrated in Figure S2."}

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