Development of Cascaded Reactive Confined Impinging Jets Micromixing: A Continuous Production of Gel Hand Sanitizer with Antimicrobial Complex Nanoparticles

Hand hygiene is crucial for suppressing a spread of infectious diseases, e.g., the COVID pandemic. Unlike solid or liquid soaps, a gel hand sanitizer (GHS) can be used in circumstances of a water shortage and suitable for outdoor usages. A hydro-alcoholic gel formation requires mixing a viscous aqueous solution of a thickener with an alcohol solution of a gelling reagent. The homogeneity of the mixing and the gelling reaction dominantly affects the product quality and the expiration period. Moreover, a GHS is typically only able to kill the pathogens rather than also to inhibit a successive pathogen growth. To overcome this mixing issue as well as prolong antimicrobial persistence, this study employs a confined impinging jets (CIJ) microreactor to generate a GHS with suspending antimicrobial nanoparticles of carboxymethyl chitosan (CMC)/Zn(II)/proanthocyanidins (PAC) via the reactive flash nanoprecipitation (RFNP), intensifying shear thinning in turbulent mixing. The process is continuous, effective and energy-saving. The developed device is compact but capable to massively produce the GHS. Meanwhile, the gel homogeneity can be guaranteed. The GHS with the suspending complex nanoparticles demonstrates superior and persistent antimicrobial performances to the bacteria of either Escherichia coli or Staphylococcus aureus as well as the fungi of Penicillium digitatum.