Precise and programmable control of reversible deformations of hydrogels has important implications for bionics. This work reports on programmable three-dimensional (3D) deformations and thermoresponsive actuation of polymer hydrogels in a well-defined manner. Precise infiltration of Fe3+ with periodic patterns is additionally used to cross-link the local polymer network through ionoprinting with a patterned electrode array. The patterned Fe3+ cross-linking generates periodic undulations in cross-link density, stiffness, and thermoresponsiveness. The internal stress induces 3D helical structures with tunable chirality and dimensions. The differential thermoresponsiveness imbues a fourth dimension to the shape deformations. Moreover, sequential ionoprinting generates well-defined in-plane periodic distributions of differential modulus and responsiveness, leading to 3D/4D umbrella-like origami upon temperature triggers.
Keywords: 3D/4D morphing; actuation; ion cross-linking; origami; responsive hydrogels.