Electrostatically Integrated Cationic Antimicrobials Modulate Hydrogel Stability, Release, and Antibacterial Activity

Hydrogel platforms for antimicrobial medical devices requiring sustained function must maintain bactericidal activity without compromising mechanical stability or cytocompatibility. Conventional systems often rely on passive antimicrobial loading, which can lead to burst release, rapid payload depletion, and dose-dependent toxicity. Here, we developed an ionic-covalent hydrogel platform in which cationic antimicrobial agents (CAAs) were post-loaded into a sulfonate-rich anionic network designed to provide electrostatic retention. A citrate-cross-linked chitosan-polyacrylamide network was coupled with poly(3-sulfopropyl acrylate) (polySPA) and subsequently loaded with benzalkonium chloride (BAK) or poly(hexamethylene biguanide) (PHMB). CAA loading reduced swelling and dry-mass loss while converting the anionic phase into a regulated antimicrobial reservoir. Compared with physically loaded controls, BAK- and PHMB-containing polySPA hydrogels sustained antimicrobial release over 28 days, retained direct antibacterial activity against Staphylococcus aureus and Escherichia coli after 28 days of release aging, reduced viable bacteria in established biofilms by up to 99%, and showed lower hemolysis after 2 h and higher L929 cell viability after 24 h than physically loaded controls. BAK also reinforced the hydrogel network, with CPMSB-3 reaching nearly 13 MPa dry tensile strength and retaining approximately 2.5 MPa wet tensile strength. In a catheter demonstration, the optimized BAK-containing hydrogel improved lubrication and retained antibacterial activity and restricted Proteus mirabilis catheter-surface migration. A subsequent 7-day pilot rat catheter challenge provided exploratory macroscopic observations but was not used as definitive evidence of in vivo anti-infective efficacy. These findings support electrostatic CAA integration as a structure-property-function strategy for antimicrobial hydrogel interfaces with sustained function.