Penicillin g

Primary human gingival fibroblasts (FB) and osteoblasts (OB) were purchased from Provitro (Berlin, Germany). Human oral keratinocytes (OK) were purchased from ScienCell (San Diego, USA). The cells were routinely cultured at 37 °C/5% CO₂ and kept in the recommended growth medium until reaching the required number of cells. Dulbecco’s Modified Eagle Medium for fibroblasts and osteoblasts (DMEM, Thermo Fisher Scientific Inc, Waltham, USA) was supplemented with 10% foetal bovine serum (FBS, Thermo Fisher Scientific Inc, Waltham, USA) and 1% antibiotics (100 U/ml penicillin G, 100 μg/ml streptomycin, Biochrom, Berlin, Germany). Additionally, 1% l-Glutamine (Biochrom, Berlin, Germany) was added to the OB medium. Human oral keratinocytes (OK) were grown in serum-free oral keratinocyte medium (ScienCell, San Diego, USA) or in Dulbecco’s Modified Eagle’s Medium/Nutrient Mixture F-12 Ham (DMEM/F-12, Sigma Aldrich, St. Louis, USA). DMEM/F12 was supplemented with 1% antibiotic solution (100 U/ml penicillin G, 100 μg/ml streptomycin, Biochrom, Berlin, Germany) and 1% or 5% serum-replacement solution (KnockOut serum replacement (KO-SR, Thermo Fisher Scientific Inc, Waltham, USA). Experiments were performed with FB, OB and OK between passages 3 and 10 in triplicate. Trypsin/EDTA solution (Biochrom, Berlin, Germany) was used for passaging monolayer cultures.

The variant of SARS-CoV-2 used was SARS-CoV-2 München (SARS-CoV-2M; [27 (link)]). The isolate was handled under the appropriate safety precautions in a BSL-3 facility (Freie Universität Berlin, Department for Veterinary Medicine). The virus used for the testing procedure was propagated on Vero E6 cells (ATCC CRL-1586; https://www.lgcstandards-atcc.org/products/all/crl-1586.aspx, accessed on 13 August 2021) in Minimum Essential Medium–Eagle with Earle’s BSS (Lonza, Basel, Switzerland) supplemented with 10% fetal bovine serum (PAN Biotech, Aidenbach, Germany), 100 IU/mL penicillin G, 100 µg/mL streptomycin (Biochrom AG, Berlin, Germany) and 1% NEA (Biochrom AG, Berlin, Germany). This specific medium does not contain phenol red and HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), a zwitterionic sulfonic acid buffering agent. The medium was chosen to prevent an interaction of treated textiles with the mentioned substances due to electrical charges. Virus titrations were performed in 96-well plates on Vero E6 cell in DMEM High Glucose supplemented with 10% fetal bovine serum and 100 IU/mL penicillin G and 100 µg/mL streptomycin.

For all aerosol experiments, an FCoV strain was used as a surrogate for SARS-CoV2. It was provided by the Friedrich Loeffler Institute (FLI, Isle of Riems, Germany; viral registration number RVB-1259).
The FCoV virus was propagated on Crandell-Rees Feline Kidney (CRFK) cells (ATTC CCL-94; https://www.lgcstandards-atcc.org/Products/All/CCL-94.aspx?geo, accessed on 13 August 2021) in DMEM High Glucose supplemented with 10% fetal bovine serum (PAN Biotech, Aidenbach, Germany), 100 IU/mL penicillin G and 100 µg/mL streptomycin (Biochrom AG, Berlin, Germany). In detail, CRFK cells were grown in T-175 tissue culture flasks (Sarstedt, Nürmbrecht, Germany) and infected with 400 µL of FCoV virus with a titer of approximately 10^5.5 median tissue culture infectious dose ₅₀ (TCID₅₀)/mL. After a three-day incubation period at 37 °C in a 5% CO₂ atmosphere, flasks were frozen at −20 °C for at least 24 h. Afterward, the virus-containing cell culture medium in the flasks was thawed and cell detritus was removed by centrifugation. The virus concentration of the supernatant was determined and stored at −80 °C until usage. For aerosolization, the concentration was adjusted to approximately 10^6.225 TCID₅₀/mL for each of the experiments.