Repetitive Bacterial Disinfection of Respirators by Polydopamine Coating

To solve the current and future mask shortage problems, developing methods of disinfecting respirators is essential, where none of the existing methods have been successfully utilized until recently. Herein, we introduce a novel method of conferring antibacterial activity to the main filtering material (i.e., polypropylene (PP)) of a respirator through sequential polydopamine (PDA) coatings. Two-step dip-coating in dopamine solution, which corresponds to one complete cycle, produces stable PDA films at the interface of the filtering material, which subsequently locally generates H₂O₂ that can be further transformed into hydroxyl radicals to inactivate pathogens. Specifically, the primary dip-coating creates a scaffold PDA film that acts as a mechanical support, and anchoring dopamine, which substantially produces H₂O₂, is immobilized to the scaffold PDA during the subsequent secondary dip-coating process. The antibacterial activity was confirmed by bacterial tests using Escherichia coli. In short, the number of colonies after incubation of the polypropylene filter with and without the PDA coating in the bacterial solution was compared. The number of bacteria in the PDA-coated sample (0.54 × 10⁹ CFU/mL·cm²) was significantly reduced compared to that in the original PP sample (0.81 × 10⁹ CFU/mL·cm²), demonstrating a positive relationship with the H₂O₂ production. Moreover, this antibacterial ability can be maintained by simply utilizing additional PDA coatings, suggesting that the respirators can be recycled. Finally, the in vitro cytotoxicity was confirmed by the CCK-8 assay, which demonstrated that the PDA-coated PP filter is biocompatible. We believe that the newly proposed method for disinfection of respirators may substitute conventional methods and can be used to alleviate the mask shortage problem.