Graphitic Carbon Nitride (g-C ₃ N ₄ )-Triggered Interfacial Radical Polymerization for Growing Hydrogel Coatings on Diverse Substrates

Controllable growth of hydrogel coatings on diverse substrates is highly desirable yet remains challenging due to the lack of universal and straightforward fabrication strategies. Herein, we present a visible-light-activated, surface-catalyzed radical polymerization approach that enables the controllable in situ construction of hydrogel coatings on a broad spectrum of materials. The process initiates with the deposition of a P(DMA- co -MEA)@g-C 3 N 4 adhesive primer layer, which not only establishes robust interfacial anchoring to the substrate but also functions as a photocatalytic initiator under visible-light irradiation. This interfacial activation drives spatially confined polymerization, yielding uniform hydrogel coatings with precisely tunable thickness. The method demonstrates extensive substrate compatibility─including metals, polymers, and inorganic materials─and readily affords programmable surface functionalities through interfacial chemical design to impart antifouling, lubricating, or biocompatible properties. Owing to its universality, strong interfacial adhesion, and operational simplicity, this strategy provides a versatile platform for the functional tailoring of irregular and three-dimensional surfaces and holds substantial potential for applications in surface/interface engineering and biorelated technologies.