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Stimulus-responsive hydrogels are an important member of smart materials owing to their reversibility, soft/wet properties, and biocompatibility, which have a wide range of applications in the field of intelligent actuations. However, poor mechanical property and complicated fabrication process limit their further applications. Herein, we report a light-responsive tissue paper/hydrogel composite actuator which was developed by combining inkjet-printed tissue paper with poly(N-isopropylacrylamide) (PNIPAM) hydrogel through simple in situ polymerization. Due to the high strength of natural tissue paper and the strong interaction within the interface of the bilayer structure, the mechanical property of the composite actuator was highly enhanced, reaching 1.2 MPa of tensile strength. Furthermore, the light-responsive actuation of remote manipulation can be achieved because of the stamping graphite with high efficiency of photothermal conversion. Most importantly, we also made a few remotely controlled biomimetic actuating devices based on the near-infrared (NIR) light response of this composite actuator. This work provides a simple strategy for the construction of biomimetic anisotropic actuators and will inspire the exploration of new intelligent materials. [ABSTRACT FROM AUTHOR]

• PPy-coated P(NIPAM-ABP) electrospun nanofiber can provide high strength. • PPy-coating by in situ polymerization can provide high light-responsive. • The actuator owns ultrafast deformation and rapid recovery. • The actuator can realize various 3D programmable complex deformations. • We have explored new biomimetic devices based on the advantages of the actuator. Intelligent hydrogels are promising for biomimetic actuators, but acquiring actuations with both high speed and powerful force is still extremely difficult. Herein, a new robust polypyrrole (PPy)-coated copoly(isopropylacrylamide-4-benzoylphenyl acrylate) [P(NIPAM-ABP)] electrospun light-responsive hydrogel is explored. The (PPy)-coated P(NIPAM-ABP) hydrogel can be obtained via in-situ polymerization of pyrroles on the nanofiber-oriented electrospun P(NIPAM-ABP) hydrogel. Compared with original P(NIPAM-ABP) hydrogel, this PPy-coated P(NIPAM-ABP) hydrogel can integrate highly-enhanced mechanical strength (from 1.21 to 5.12 MPa of tensile strength) and ultrahigh-efficiency of photothermal conversion together. In addition, the orientation of P(NIPAM-ABP) nanofibers can still maintain well for programmable complex deformations. Consequently, the as-prepared robust bi-hydrogel actuator with ultrafast and complex deformations has been achieved, through bonding the PPy-P(NIPAM-ABP) hydrogel membrane with a polyethylene glycol diacrylate-cellulose nanofiber (PEGDA-CNF) composite hydrogel membrane via interfacial ultraviolet (UV) polymerization of PEGDA monomers. Several light-responsive biomimetic actuating devices have been achieved, which owning powerful force (can grab up 100 times of self-weight), rapid speed (1285.71°/s of folding) or precisely programmable complex deformations. Furthermore, two biomimetic devices with synergistic functions of the three advantages above have been explored, which can mimic the child's sit-up and the starfish's continuous crawling movement respectively. This work provides a robust remotely-controlled light-responsive hydrogel actuator with powerful force, ultrafast speed and programmable complex actuations, which will inspire the design and fabrication of novel soft biomimetic actuating materials and systems. [ABSTRACT FROM AUTHOR]

Near-infrared light-responsive hydrogel actuator with complex deformations and remote precise control is fabricated from the natural bamboo. The resulting biomimetic bamboo/PNIPAM hydrogel actuator can be precisely designed to perform a variety of simulations. [Display omitted] • Biomimetic actuators based on anisotropic natural bamboo were prepared. • Nigrosine was first used to fabricate light-responsive hydrogel actuator. • The actuator exhibits outstanding programmability and remote-control performance. • The actuator can move freely on the water surface based on Marangoni effect. Near-infrared light-responsive hydrogels are one of the most important soft biomimetic actuators owing to their accuracy, remote control performance, and permeability. However, the complex deformations and materials of hydrogel actuators are still a serious challenge. Herein, we have developed a novel composite hydrogel actuator by combining natural bamboo sheet and nigrosine/poly(N-isopropylacrylamide) (PNIPAM) composite hydrogel. The high-efficient photothermal conversion of the nigrosine/PNIPAM composite hydrogel sheet generates light-responsive actuation that is remotely controllable. Furthermore, the bamboo sheet with fiber-oriented structure can be cut at different angles, which facilitates programmable 3D complex deformations in the actuator. Accordingly, we have designed a series of biomimetic actuating devices, including simulations of butterfly antenna, Dendrobium , smart switch, and even a multi-step deformational biomimetic claw. In addition, we also explored a biomimetic insect with precisely-controlled fast movements on the water surface based on Marangoni effect. This work provides a simple but general strategy for fabricating biomimetic actuators and will inspire new designs for intelligent soft actuators. [ABSTRACT FROM AUTHOR]