Soft actuators, which can convert external environmental stimuli into mechanical energy, have allured increasing interest recently due to their promising applications in sensors, robots, artificial muscles, medicine, etc. Recently, aiming at achieving robust actuation with adaptable manipulation in complicated environments, several kinds of soft actuators have been designed, which include liquid crystal elastomer actuators, composite actuators, hydrogel actuators, etc. Among others, inspired by the motion of plants whose winding and curving are driven by the absorption or dehydration of water in the cells and tissues, hydrogel actuator has attracted more and more attention, which is capable of undergoing a deformation as large as 10 times of its own volume by changing the amount of water in its network. This unique property, together with their wetness and biocompatibility, makes the hydrogel actuators particularly useful in applications ranging from smart chemical valves, tissue scaffold engineering to chemical reaction switches, and drug delivery vehicles.
The actuation of a hydrogel actuator relies on the swelling and de-swelling process caused by the osmotic-pressure changes when exposed to these stimuli, which is slow and requires the presence of water environment. Due to the slow diffusion of water in and out of the hydrogel networks, even a slight volume shift (about 10%) of the hydrogel actuator takes several minutes or even hours, which hinders its practical application scope. It still remains a challenge to achieve both high-speed, fast response, and in-air motion for the hydrogel actuators.
Recently, the research group of Prof. Bin Dong reports a high performance in-air hydrogel actuator, which is composed of a binary iron oxide nanoparticle (IONP, i.e. Fe3O4NP) and poly(sodium acrylate) (PAANa) hydrogel composite. Interestingly, it exhibits ultrafast motion, which can reach 1.6 m/s speed and a superior jumping height of 15 cm with fast response time of only 800 ms. The extraordinary performance of the current hydrogel actuator is realized by harnessing the synergetic interactions between the elasticity of the hydrogel and the bubble caused by the photothermal effect of the embedded IONPs. More interestingly, both jumping and rolling behaviors exhibit controllable moving velocities and directions, which make the hydrogel actuator reported in the current study attractive for various practical applications. In addition, the research group has demonstrated its potential use in the fields of sound-recording and cargo delivery robotics.
The PhD candidate, Mongtong Li, from Prof. Bin Dong’s group, is the first author of this article, and Xin Wang is the co-first author. This work is supported by MCF 2018YFE0306105 and NSFC 21574094 project.
Author information：Mingtong Li, Xin Wang, Bin Dong*，Metin Sitti*
Article link：https://www.nature.com/articles/s41467-020-17775-4
Prof. Bin Dong’s webpage：http://funsom.suda.edu.cn/7f/a8/c2735a32680/page.htm
Editor: Danting Xiang