Programmable and Bidirectional Bending of Soft Actuators Based on Janus Structure with Sticky Tough PAA-Clay Hydrogel

Abstract

Facile preparation, rapid actuating, and versatile actions are great challenges in exploring new kinds of hydrogel actuators. In this paper, we presented a facile sticking method to prepare Janus bilayer and multilayer hydrogel actuators that benefited from a special tough and adhesive PAA-clay hydrogel. Combining physical and chemical cross-linking reagents, we endowed the PAA gel with both toughness and adhesion. This PAA gel was reinforced by further cross-linking with Fe. These two hydrogels with different cross-linking densities exhibited different swelling capabilities and moduli in the media manipulated by pH and ionic strength, thus acting as promising candidates for soft actuators. On the basis of these gels, we designed hydrogel actuators of rapid response in several minutes and precisely controlled actuating direction by sticking two hydrogel layers together. Elaborate soft actuators such as bidirectional bending flytrap, gel hand with grasp, open, and gesturing actions as well as word-writing actuator were prepared. This method could be generalized by using other stimuli-responsive hydrogels combined with the adhesive PAA gel, which would open a new way to programmable and versatile soft actuators.

pH and Thermo Dual‐Responsive Fluorescent Hydrogel Actuator

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properties upon the trigger of certain stimuli. [7][8][9][10][11][12] Conventional hydrogels only have single-performance alternation in response to environmental stimuli. [13][14][15][16][17][18] Hydrogels that could change two or more properties triggered by external conditions will own a wider range of potential applications; therefore, it is significantly important to develop hydrogels that could alter multiple properties upon external trigger.

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Shape changing hydrogels and their applications as soft actuators

“…[22][23][24][25][26][27][28][29][30][31][32][33][34] The two hydrogel layers are always connected with interpenetrating polymer network, [22][23][24][25][26][27][28][29][30]35,36 host-guest interaction 31,33 , or electrostatic interaction. 32,34 Hu et al firstly prepared a bilayer hydrogel by combining a layer of polyacrylamide (PAAM) hydrogel and a layer of poly (N-isopropylacrylamide) (PNIPAM) hydrogel through interpenetrating polymer network. 22 The thermoresponsive PNIPAM layer shrinks or swells upon heating and cooling, inducing the bending/unbending of the bilayer hydrogel strips.…”

A Fast, Reversible, and Robust Gradient Nanocomposite Hydrogel Actuator with Water‐Promoted Thermal Response

“…Both response performance and mechanical properties are critical to thermoresponsive hydrogels. Bilayer structure is one of the most widely used strategies for enhancing response performance of hydrogel actuators . Although this novel strategy might be used to fabricate bionic arms or soft robots, their complex assembly requires multiple parts to be processed and the interfacial surface of the two connecting gels is prone to cracking during repeated deformation or movement.…”

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for enhancing response performance of hydrogel actuators. [7,15,16] Although this novel strategy might be used to fabricate bionic arms or soft robots, their complex assembly requires multiple parts to be processed and the interfacial surface of the two connecting gels is prone to cracking during repeated deformation or movement. Besides, the swelling of gels in water leads to poor interface compatibility, thus making these gels difficult to endure external stress.

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