Anisotropic Hydrogels Constructed via a Novel Bilayer-Co-Gradient Structure Strategy toward Programmable Shape Deformation

The bilayer hydrogel actuators have attracted extensive attention for their unique stimulus-responsive properties. Most of the current research studies only focused on changing the constituent materials of two layers in the fixed bilayer structure to enhance the responsive deformability of bilayer hydrogels without involving the exploration on a structural level, which limited its further development. In this study, we proposed a novel bilayer-co-gradient structure constructed via a simple and low-cost structural programming strategy, which was self-assembled by introducing an embedded gradient structure into a single bilayer structure with the assistance of gradient-dissolved oxygen in nature. This multistructure endowed the hydrogel with a faster bending response than a single bilayer structure due to the synergistic asymmetry of the simple bilayer structure and the embedded gradient structure. It was found that the prepared hydrogels exhibited significantly anisotropic electrical conductivity and swelling properties. Moreover, the stimulus-responsive shape deformation exhibited superior temperature- and pH-based deformation programmability. Additionally, this hydrogel could serve as a hydrogel gripper to perform grasping behavior, which demonstrated that our study opens up a new route for designing and fabricating smart actuators.