A recent breakthrough in the design of photothermal actuator has been achieved by a research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences. 

Led by Profs. TIAN Xingyou and ZHANG Xian, the researchers developed a novel superstructure liquid metal/low expansion polyimide/polydimethylsiloxane (LM@PI/PDMS) actuator, which combines rapid motion with impressive load carrying capacity-an achievement that has eluded previous actuator designs.

"The design mimics the structure of leaf veins," said LI Xiaofei, a member of the team, "which balances the strength and speed of the actuator." 

The results were published in Advanced Materials.

Photothermal actuators have traditionally faced a dilemma: thin actuators can move quickly but lack strength, while thicker actuators can carry more weight but respond more slowly. Liquid metal (LM)-based actuators had shown promise, but have yet to solve this problem, as the LM microspheres provide thermal properties without significantly improving material strength.

In this study, inspired by the leaf's microvascular network, the researchers used laser etching to create intricate graphene trenches within the LM@PI films. These trenches were then encapsulated with PDMS to produce a programmable actuator that retains both speed and load-carrying capabilities. The leaf vein-inspired structure allows the actuator to respond quickly while maintaining strength and durability.

The new actuator design combines the fast response of lightweight materials with the load-carrying strength of thicker materials. The researchers demonstrated the potential of these actuators by creating a photo-activated robotic dog that can crawl, jump, swim, and stand, as well as single-pole triple-throw switches and high-speed oscillators.

By introducing superstructures into the design, this research opens up new ways of designing actuators that are faster, stronger, and more versatile, with wide-ranging applications in robotics and intelligent systems.

Superstructure liquid metal photothermal actuator inspired by leaf veins. (Image by LI Xiaofei)