In vitro testing of salt coating of fabrics as a potential antiviral agent in reusable face masks

During the coronavirus disease (COVID-19) pandemic, wearing face masks in public spaces became mandatory in most countries. The risk of self-contamination when handling face masks, which was one of the earliest concerns, can be mitigated by adding antiviral coatings to the masks. In the present study, we evaluated the antiviral effectiveness of sodium chloride deposited on a fabric suitable for the manufacturing of reusable cloth masks using techniques adapted to the home environment. We tested eight coating conditions, involving both spraying and dipping methods and three salt dilutions. Influenza A H3N2 virus particles were incubated directly on the salt-coated materials, collected, and added to human 3D airway epithelial cultures. Live virus replication in the epithelia was quantified over time in collected apical washes. Relative to the non-coated material, salt deposits at or above 4.3 mg/cm(2) markedly reduced viral replication. However, even for larger quantities of salt, the effectiveness of the coating remained dependent on the crystal size and distribution, which in turn depended on the coating technique. These findings confirm the suitability of salt coating as antiviral protection on cloth masks, but also emphasize that particular attention should be paid to the coating protocol when developing consumer solutions.