Liquid-Coated Air and Water Filters Resist Bacterial Biofouling

During the purification of water and air, the adhesion of bacteria and other foulants is an ongoing issue that leads to flux decline, and current chemical and physical cleaning methods for fouled filters can lead to filter degradation over time. In addition to being porous throughout, commonly used filtration materials such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) often have a textured surface that promotes the adhesion of bacteria and other contaminants. In this work, we present bioinspired liquid-coated filters as a new approach to creating filters that resist fouling. Liquid-coated filters were created by immobilizing a water immiscible liquid on the surface of commercially available synthetic filters. For water filtration tests, 0.45 µm pore diameter PTFE and PVDF filters were coated with omniphobic perfluoropolyether liquids. We measured the continuity of the surface liquid layer by testing how easily a water droplet could begin to move the surface, as well as the anti-adhesion properties of the surface liquid layer through quantifying the speed of a droplet’s movement at a static angle of inclination. The results indicate that infused PTFE membranes form a superhydrophobic surface with a sliding angle of approximately 5°. Infused PTFE membranes sustained a more consistent functional liquid layer, with an approximately 75% lower sliding angle and 70% faster droplet movement at a fixed angle, than the infused PVDF. We measured the ability of the infused membranes to resist biofilm formation by incubating in growth media with <i>Staphylococcus epidermidis </i>for 24 hours. Infused PVDF membranes reduced biofilm formation by approximately 25% compared to bare controls while infused PTFE membranes reduced biofilm formation by approximately 98%. Pure water permeability (PWP) experiments conducted at an applied pressure of 1.5 bar indicated that liquid-coated PVDF membranes had a statistically equivalent PWP of 2827 ± 323 L/m²-h-bar, for over 10 cycles of use, showing that the immobilized liquid is present and stable within the pores. For aerosol filtration, we tested the efficiency in capturing and releasing aerosolized <i>Escherichia coli </i>using liquid-coated commercial PTFE and HEPA filters. We determined that bacteria trapped on the liquid-coated filters could be removed with increased efficiency compared to bare controls. The use of liquid-coated materials in water and air purification applications opens new doors for the creation of a biointerface that resists adhesion in dynamic environments.