Poly( <i>N</i> -isopropylmethacrylamide) Nanohydrogel Coatings to Limit the Adhesion of Microorganisms in Drinking Water Distribution Systems: Stability and Optimization

Biofilm formation in drinking water distribution systems (DWDSs) presents a significant challenge, compromising both water quality and infrastructure lifetime. Recently, a nanohydrogel coating was demonstrated to have excellent antiadhesive properties toward drinking water microorganisms, making it a promising approach to alleviate biofilm formation in DWDS systems. However, the used coating procedure was not suitable for large surface areas and the stability of the coating under various physicochemical conditions was not assessed. This study proposes an optimized coating procedure for poly-(vinyl chloride) (PVC)-based drinking water piping and evaluates the stability of this poly-(<i>N</i>-isopropylmethacrylamide) (PNIPAM) based nanohydrogel coating and its ability to prevent microbial adhesion under drinking water conditions. Stability was assessed through detailed scanning electron microscopy, atomic force microscopy, and contact angle measurements after accelerated stress tests under different physicochemical conditions, including temperature, pH, salt concentration, and surfactant concentration. Microbial adhesion was tested in 35 day long recirculation experiments performed in a lab-scale DWDS under relevant drinking water conditions. The coating exhibited a very high stability under harsh pH conditions (1.5-13.5), high and low temperatures (4-70 °C) and extreme salt concentrations (0.1-6000 mM). However, at high surfactant concentrations, above the critical micellar concentration, some instability was observed. Against DWDS conditions, the coating remained stable over 35 days, showing a significant reduction (>80%) in adhesion of microorganisms. Overall, these findings support the use of the PNIPAM nanohydrogel coating as a scalable and stable solution to microbial adhesion in drinking water environments, offering a promising alternative or support to disinfection treatments to reduce biofilm formation in DWDS systems but with high potential toward other applications due to the highly stable nature of the nanohydrogel coating.