An Anisotropic Hydrogel Actuator Enabling Earthworm‐Like Directed Peristaltic Crawling

Abstract

Peristaltic crawling,which is the moving mechanism of earthworm-like limbless creatures in narrow spaces,i s ac hallenging target to mimic by using soft materials.Here we report an unprecedented hydrogel actuator that enables not only ap eristaltic crawling motion but also reversing its direction. Our cylindrically processed hydrogel contains gold nanoparticles for photothermal conversion, at hermoresponsive polymer network for switching the electrical permittivity of the gel interior,and cofacially oriented 2D electrolytes (titanate nanosheets;T iNSs) to synchronously change their anisotropic electrostatic repulsion. When ah ydrogel, whichw as designed to include cofacially oriented TiNSs along the cylindrical gel axis,i sp ointwisely photoirradiated with av isible-light laser,i t spatiotemporally expands immediately (< 0.5 s) and largely (80 %ofits original length) in an isovolumetric manner.When the irradiation spot is moved along the cylindrical gel axis,the hydrogel undergoes peristaltic crawling due to quicka nd sequential elongation/contraction events and moves oppositely towardt he laser scanning direction. Thus,w hen the scanning direction is switched, the crawling direction is reversed. When gold nanorods are used in place of gold nanoparticles,t he hydrogel becomes responsive to an ear-infrared light, which can deeply penetrate into bio tissues.

Hydrogel‐Based Artificial Muscles: Overview and Recent Progress

“…The ideal way to increase the output force and response speed might be to increase the driving force of the actuation. There are several approaches such as increasing the concentration of functional moiety, increasing the intensity of stimuli, and incorporating nanomaterials to provide driving force, which has been generally applied . Recently, 3D‐printed hydrogel‐based gripper demonstrated substantial output force, over 100 times the weight of the actuator, which was comparable with elastomer‐based actuator .…”

“…A conventional method of preparing light‐responsive hydrogels using the light stimuli to indirectly induce the deformation of hydrogels that are prepared based on the temperature‐ or pH‐sensitive hydrogel as the mother matrix. For example, light irradiation can trigger the deformation of temperature‐sensitive hydrogels that contains photothermal materials, such as gold nanoparticle (AuNP) and chlorophyllin . For pH‐responsive hydrogels that contains light‐responsive ionizable functional groups, irradiation induces the release of proton or hydroxyl ions from light‐responsive ionizable groups, resulting in pH alteration and subsequent deformation of the pH‐sensitive hydrogel …”

“…Copyright 2018, American Chemical Society. D) Adapted with permission [23]. Copyright 2018, Wiley‐VCH.…”

“…The example shown in Figure D also shows exceptional system and results. A hydrogel‐based artificial muscle is prepared from a mixture of temperature‐responsive PNIPAM network, oriented titanate nanosheet (TiNS) by magnetic field, and AuNP via subsequent photopolymerization (Figure D‐i) . Due to the photothermal effect of AuNPs, response of the hydrogel can be stimulated by near‐infrared (NIR) light irradiation.…”

“…Some hydrogel locomotors could restrictively be operated on the surface which have specific geometry . However, well‐designed novel systems presented locomotion on flat surface (Figure D), and unprecedented earthworm‐like motion in capillary (Figure E) …”