Digital Regulation Of Bidirectional Gradients In Stimuli-responsive Hydrogels And Their Deformation Studies

Stimuli-responsive hydrogels have attracted tremendous interests due to their promising applications in soft robots,tissue engineering and actuators.Recently,various stimuli-responsive hydrogels based on bilayer structure,gradient structure and patterned structure has been reported.The bilayer and gradient structures generally only enable simple bending and buckling deformation.Although the patterning of anisotropy structures can be used for the construction of stimuli-responsive hydrogels capable of complex 3D deformations,the strategy is limited by the ultrahigh difficulty of fabrication and the incompatibility/delamination risk of different responsive materials.Currently,it still lacks of broadly applicable method to prepare the stimuli-responsive hydrogels with ability of complex biomimetic deformations.This study presents two simple and general strategies for digitally programing the bidirectional(i.e.,longitudinal and transverse)gradients of stimuli-responsive hydrogels.1.Based on UV asymmetric polymerization,a variety of stimuli-responsive hydrogels with complex patterned gradient structures have been prepared through patterning the UV exposure time via photomasks.The SEM and conversion rate tests shows that different UV exposure times result in different monomer conversion rates and induce the formation of different gradient structures.The influence of gradient structure on deformation dynamics has been clarified,and various ultra-complex bionic shape transformations have been achieved,such as the deformable Miura folding structure,the gesture changes in guessing punch games,moving octopus,etc.Besides,the gradient hydrogels have been demonstrated as sensors for time switch application in smart circuits.2.Based on the competition effect of photopolymerization and thermopolymerization,the precise modulating of anisotropic structures of stimuli-reponsive hydrogels has been realized.Various stimuli-responsive hydrogels with complex patterned gradient structure have been prepared.The feasibility of the strategy has been confirmed by SEM and conversion rate tests.Through systematically studying the influence of gradient structures on deforming dynamics,various complex biomimetic shape transformations have been achieved by the pattering the gradient structures.