Confinement controlled swelling mechanisms of hydrogels in multi-material architectures

• Establishes a mechanics-based framework for hydrogel swelling under geometric confinement and rigid interfacial constraints in multi-material architectures. • Clarifies the roles of geometric confinement and interfacial rigidity in regulating nonlinear deformation, stress localization, and stress evolution during swelling–deswelling cycles. • Demonstrates predictable, time-dependent structural regulation driven purely by confinement-controlled swelling, without external energy input. • Integrates structural modeling, cyclic experimental validation, and multi-material vat photopolymerization to enable programmable soft–rigid systems. Responsive swelling of hydrogels is widely used in soft materials and microfluidic systems, yet deformation mechanisms under multi-material confinement, especially during cyclic swelling and deswelling, remain insufficiently understood. In this study, we investigate hydrogel swelling response mechanisms under combined geometric confinement and rigid interfacial constraints in multi-material architectures fabricated by multi-material vat photopolymerization. A poly(4-acryloylmorpholine-co-2-(2-ethoxyethoxy) ethyl acrylate) hydrogel is employed as a model system to systematically examine confined swelling and deswelling behavior. By coupling the intrinsic cyclic swelling response of the hydrogel with mechanical constraints imposed by a rigid, hydrophobic photosensitive resin substrate, we reveal how geometric boundary reinforcement and multi-material interfacial interactions jointly govern deformation stability and stress evolution during repeated swelling cycles. Quantitative relationships are established between confinement parameters, cyclic swelling-induced deformation, and mechanical response reproducibility. Based on this mechanistic framework, a microfluidic channel is demonstrated to illustrate how confinement-controlled hydrogel swelling enables predictable channel regulation without external energy input. These results provide a quantitative understanding of hydrogel swelling interactions in multi-material environments and offer a mechanistic foundation for designing self-regulated functions in soft integrated systems.