Core-Shell Nanoparticle Additive Enables High-Efficacy Antimicrobial Coatings

Microbial proliferation on surfaces poses a persistent challenge for applications requiring hygienic or sterile environments. Hydantoin-based antimicrobials are attractive N-halamine precursors because of their rapid biocidal activity, low toxicity, and long-lasting functionality. Hydantoin-based monomers, such as hydantoin acrylamide (HA), have previously been used to synthesize copolymers with potent antimicrobial properties. However, their practical application in waterborne coatings is limited by the high cost and poor aqueous solubility of HAs. Here, a core-shell (CS) particle architecture consisting of a polystyrene core and a poly(hydantoin acrylamide) (PHA) shell is reported to address these limitations. This design reduces HA usage by approximately 65% while preserving antimicrobial performance, resulting in nearly 3-fold reduction in material costs. In addition, the CS particles exhibit an 18-fold increase in solid loadings and 20-35% smaller particle sizes compared with pure PHA particles. Upon activation with dilute chlorine bleach (20-100 ppm), antimicrobial N-halamines were successfully generated on the particle surface, with CS particles showing approximately 10% higher oxidative chlorine levels compared to pure PHA particles dispersed in aqueous suspension. When incorporated into waterborne coatings, the CS particles enabled fully rechargeable antimicrobial films with high efficacy. Dried coating films could be recharged by using a simple bleach treatment over at least five recharge cycles. Contact killing experiments against Staphylococcus aureus and Escherichia coli demonstrated 100% bacterial killing within 30 min at 3% additive loading. Overall, our CS approach establishes an efficient and scalable route for producing durable antimicrobial additives that can be readily integrated into waterborne coating systems without modification of primary film chemistry.