Transparent Copper-Loaded Chitosan/Silica Antibacterial Coatings with Long-Term Efficacy

Bacteria-contaminated inanimate surfaces within hospitals and clinics result in transmission of pathogens via direct or indirect contact, leading to increased risk of healthcare-associated infections (HAI). The use of antibacterial coatings is a potential way of reducing the bacterial burden, but many surfaces such as instrument panels and monitors necessitate the coatings to be transparent while being highly antibacterial. In this work, silica nanoparticles (SiO₂ NPs) were first grown over a layer of acrylated quaternized chitosan (AQCS) covalently immobilized on commercially available transparent poly(vinyl fluoride) (PVF) films. The SiO₂ NPs then served as nanoreservoirs for adsorption of copper ions. The coated PVF films were transparent and reduced viable bacterial count by ∼99% and 100%, when incubated with a bacteria-loaded droplet for 60 and 120 min, respectively. The killing efficacy of these coatings, after wiping 100 times, with a deionized water-wetted cloth was reduced slightly to 97-98%. The stability of these coatings can be further improved with the deposition of another layer of cationic quaternized chitosan (QCS) over the negatively charged SiO₂ NP layer, wherein the coatings maintained ∼99% killing efficacy even after 100 wipes. These coatings showed no significant toxicity to mammalian cells and, hence, can potentially be used in a clinical setting for reducing HAI.