An effective approach to develop a novel macroscopic anisotropic bilayer hydrogel actuator with on–off switchable fluorescent color‐changing function is reported. Through combining a collapsed thermoresponsive graphene oxide‐poly(N‐isopropylacrylamide) (GO‐PNIPAM) hydrogel layer with a pH‐responsive perylene bisimide‐functionalized hyperbranched polyethylenimine (PBI‐HPEI) hydrogel layer via macroscopic supramolecular assembly, a bilayer hydrogel is obtained that can be tailored and reswells to form a 3D hydrogel actuator. The actuator can undergo complex shape deformation caused by the PNIPAM outside layer, then the PBI‐HPEI hydrogel inside layer can be unfolded to trigger the on–off switch of the pH‐responsive fluorescence under the green light irradiation. This work will inspire the design and fabrication of novel biomimetic smart materials with synergistic functions.
Inspired by the water self-circulation mechanism that contributes to the motion of Mimosa leafs, a hydrogel actuator with a reverse thermal responsive bilayer structure was prepared, which can generate motions in water, oil and even in open-air environment.
Many living organisms have amazing control over their color, shape, and morphology for camouflage, communication, and even reproduction in response to interplay between environmental stimuli. Such interesting phenomena inspire scientists to develop smart soft actuators/robotics via integrating color‐changing functionality based on polymer films or elastomers. However, there has been no significant progress in synergistic color‐changing and shape‐morphing capabilities of life‐like material systems such as hydrogels. Herein, we reported a new class of bioinspired synergistic fluorescence‐color‐switchable polymeric hydrogel actuators based on supramolecular dynamic metal–ligand coordination. Artificial hydrogel apricot flowers and chameleons have been fabricated for the first time, in which simultaneous color‐changing and shape‐morphing behaviors are controlled by the subtle interplay between acidity/alkalinity, metal ions, and temperature. This work has made color‐changeable soft machines accessible and is expected to hold wide potential applications in biomimetic soft robotics, biological sensors, and camouflage.
wileyonlinelibrary.comWhile considerable progress of 2D deformation of SPHs has been achieved, [15][16][17][18][19][20][21][22][23] the realization of 3D or even more complex deformation still remains a significant challenge. Currently, there are two main approaches to achieve 3D complex deformations/movements of SPHs by imposing external nonuniform stimuli [24,25] or through the preparation of internal anisotropic hydrogels. [26,27] Due to the difficulty of applying most of the nonuniform external stimuli precisely onto a SPHs system, an alternative strategy of fabricating macroscopically anisotropic SPHs (MA-SPHs) has been explored as the popular way to realize complex 3D deformation. [26,27] These SPHs can accomplish diverse complex deformations directly under uniform stimuli owing to the heterogeneous responsiveness of anisotropic structures.Complex 3D deformation of the MA-SPHs could be achieved through the fabrication of differential cross-linking density [28][29][30] or a local secondnetwork [31][32][33][34][35] and subsequently applying external stimuli inside the hydrogels. For example, Sharon and co-workers have reported an early example to prepare a 2D anisotropic hydrogel sheet with laterally nonuniform cross-linking density to realize the 3D buckling or wrinkling. [28] Hayward and co-workers have introduced cross-linked stimulus-responsive polymers with UV-induced patterning to fabricate 2D hydrogel sheets with precisely controllable 3D bucklings. [29] Using a similar strategy, Wu et al. have developed an anisotropic 2D gel sheet with a tunable second-network to achieve 3D spiralings or curlings. [31] Besides UV cross-linking, an "electrically assisted ionoprinting" technique could also be utilized to form a local second-network and to attain 3D complex deformations. [32,34] Despite the recent progress of 3D complex deformation of MA-SPHs, the lack of remote-controllability during the deformation process strongly limits their application in some special fields, where solution-wide changes or invasive wires or electrodes are not permitted.With excellent photothermal conversion efficiency, [36] graphene sheets are well known as good candidates to obtain remote-controllable light-responsive deformations. However, they cannot be homodispersed in hydrogel directly because of their hydrophobic nature. Alternatively, graphene oxide sheets (GOs) can be well dispersed in hydrogels and can be reduced in situ using UV irradiation to attain reduced GOs (RGOs). Therefore, remote-controllable light-responsive deformations of As one of the most promising smart materials, stimuli-responsive polymer hydrogels (SPHs) can reversibly change volume or shape in response to external stimuli. They thus have shown promising applications in many fields. While considerable progress of 2D deformation of SPHs has been achieved, the realization of 3D or even more complex deformation still remains a significant challenge. Here, a general strategy towards designing multiresponsive, macroscopically anisotropic SPHs (MA-SPHs) with th...
Inspired by the assembly of Lego toys, hydrogel building blocks with heterogeneous responsiveness are assembled utilizing macroscopic supramolecular recognition as the adhesion force. The Lego hydrogel provides 3D transformation upon pH variation. After disassembly of the building blocks by changing the oxidation state, they can be re-assembled into a completely new shape.
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