Construction of 3D Shape‐Changing Hydrogels via Light‐Modulated Internal Stress Fields

The 3D shape‐changing hydrogels are highly pursued for numerous applications. However, up to now, the construction of complex 3D shape‐changing hydrogels remains a challenge. The reported design strategies are mainly applied to fabricate 2D ones by introducing anisotropic microstructures into hydrogel sheets/membranes. Herein, we present a convenient photolithography strategy for constructing complex 3D shape‐changing hydrogels by simultaneously modulating anisotropic microstructures and internal stress fields of gel sheets. When the precursor solution containing ultraviolet (UV) absorber is irradiated by single‐side UV light, the attenuated polymerization rate can cause the generation of asymmetric internal stress field in the resulting hydrogel sheet. In the meantime, the directional diffusion of unpolymerized monomers allows for the formation of vertical gradient structure within hydrogel. Therefore, by applying different photomasks to modulate the local gradient structures and internal stress fields of the gel sheets, they can spontaneously transform into various complex 3D shape‐changing hydrogels in the air. Response to the external stimuli, these 3D shape‐changing hydrogels (e.g., fighter plane, birdie, and multi‐storey origami lattices) can deform in a novel 3D₁‐to‐3D₂‐to‐3D₃ mode. This new design strategy contributes to the development of complex biomedical implants and soft robotics.