Sprayable Biocide-Free Polyurethane Paint that Reduces Biofouling and Facilitates Removal of Pathogenic Bacteria from Surfaces

The ability to prevent bacterial adhesion on surfaces and to facilitate the removal of bacteria once they have already contaminated or colonized a surface is important in a broad range of fundamental and applied contexts. The work reported here sought to characterize the physicochemical properties of a family of biocide-free hydrophobic polyurethane coatings containing polysiloxane segments and evaluate their ability to mitigate bacterial fouling and/or facilitate subsequent surface cleaning after exposure to pathogenic bacteria. We developed benchtop microbiological assays to characterize surface fouling and subsequent removal of bacteria after repeated (i) short-term intermittent physical contact with and (ii) longer-term continuous flow-based contact with liquid growth media containing either <i>S. aureus</i> or <i>E. coli</i>, two common Gram-positive or Gram-negative bacterial pathogens, respectively. Characterization of fouled and cleaned surfaces using fluorescence microscopy and standard agar-based plaque assays revealed significant differences in both reductions in initial fouling and subsequent cleanability after gentle rinsing with water. These differences correlated to differences in the surface properties of these materials (e.g., hydrophobicity and contact angle hysteresis), with coatings exhibiting lower contact angle hysteresis generally having the greatest antibiofouling and easy-to-clean properties. Our results suggest that these biocide-free, siloxane-containing polyurethane-based clearcoat materials show significant promise for the mitigation of surface fouling and bacterial adhesion, which could prove useful in a range of commercial applications, including in "high touch" environments where microbial contamination is endemic.