Antibacterial sustained-release coatings from halloysite nanotubes/waterborne polyurethanes

Abstract

Abstract Natural and safe antibacterial nanoparticles based on carvacrol loaded halloysite nanotubes and their waterborne polyurethane nanocomposite coatings with antibacterial and antibiofilm properties are presented. Halloysite nanotubes are natural clay nanoparticles with a hollow tubular structure that allows loading and sustained release of active agents. In this study, halloysite nanotubes were efficiently loaded with carvacrol, the active agent of essential thyme oil. Encapsulated carvacrol molecules were demonstrated to be released from halloysite nanotubes in a sustained manner over one week and effectively inhibit the growth of a pool of pathogenic microorganisms. Carvacrol loaded halloysite nanotubes were further investigated as antibacterial nanofillers in polymeric nanocomposites by incorporating them into waterborne polyurethane coatings. Polyurethane nanocomposite films containing 5 wt.% carvacrol loaded halloysite nanotubes showed uncompromised thermal and mechanical stability as compared to neat polyurethane films. Carvacrol/halloysite nanotubes/polyurethane films demonstrated sustained release of carvacrol and antibacterial activity on representative pathogens, Aeromonas hydrophila , as evidenced by growth inhibition in agar diffusion assays and reduction in bacterial count upon exposure to nanocomposite films. Furthermore, these nanocomposite films inhibited bacterial colonization on their surfaces at least for two days demonstrating their applicability as anti-biofilm surface coatings. Composed of safe and natural components, the sustained-release antibacterial coatings presented here have strong potential for being widely utilized to prevent and mitigate bacterial infections on materials surfaces without raising toxicity concerns.