Chemically Active Interfaces Enable Modular Manufacturing of DLP 3D Printed Hydrogel Electronics

Hydrogel-based flexible sensors are promising for wearable electronics, while digital light processing (DLP) printing enables customized device fabrication. However, DLP manufacturing remains largely limited to monolithic structures because freshly printed hydrogels lack sufficient mechanical stability for constructing curved or enclosed architectures. Here, a modular manufacturing strategy is developed by enabling post-printing polymerization through a sustained radical-generation system comprising Cu2+, lignosulfonate (LS), and ammonium persulfate (APS). Unlike conventional photoinitiated systems that become inactive after light exposure, the Cu2+-LS complex maintains a dynamic Cu2+/Cu+ redox cycle in the dark, continuously activating APS to generate radicals. Consequently, independently printed hydrogel modules undergo interfacial polymerization and reconstruct a continuous covalent network, enabling assembled hydrogels to exhibit bulk-like load-bearing performance with failure occurring outside the assembled interface. The Cu-LS system also introduces mobile ions, imparting intrinsic ionic conductivity for strain sensing without conductive fillers. Using this approach, ring-integrated and kirigami-patterned wearable sensors are fabricated through modular assembly. A fingertip-mounted device achieves 99% accuracy in classifying ten sign-language gestures and enables real-time intelligent wheelchair control. This work converts hydrogel interfaces from inactive boundaries into active reconstruction sites, offering a versatile route to the modular fabrication of mechanically integrated soft electronics.