Light‐Fueled Polymer Film Capable of Directional Crawling, Friction‐Controlled Climbing, and Self‐Sustained Motion on a Human Hair

Abstract

Recent efforts in stimuli-responsive soft materials have enabled wirelessly controlled actuation with increasing degrees of freedom, yielding miniature robots capable of various locomotion in open environments such as on a plane or inside fluids. However, grand challenges remain in harnessing photomechanical deformation to induce locomotion and control of friction during the movement, especially for robotic actuations within constrained spaces. Here, the authors report a centimeter-long polymer strip made of a liquid crystal network that is capable of versatile light-fueled motions along a human hair. The soft polymer robot can translocate directionally upon temporally modulated excitation and climb vertically through friction control with light. A self-oscillating strip is demonstrated to continuously translocate along the hair upon a constant light stimulus, and its gaiting is associated to the smoothness of the hair surface. The results offer new insights to small-scale photo-actuator, mechanical control, and automation in soft micro robotics.

Self-assembled liquid crystal architectures for soft matter photonics

“…13a . Cheng et al 261 demonstrated the light-controlled friction and locomotion of a centimeter-long polymer stripe under a constrained condition of a human hair, Fig. 13b .…”

“… 251 , with permission of Wiley-VCH. b Light-activated LC actuators climbing on human hairs 261 . Reproduced from ref.…”

Photothermal-Driven Liquid Crystal Elastomers: Materials, Alignment and Applications

“…Crawling is one of the simplest modes of movement. Photothermal-driven LCE soft robots can crawl in complex and extreme environments because of the softness of the body [ 7 , 27 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 ]. In addition, the robots can be made smaller because they do not need to carry a power source like traditional robots, as light can provide energy remotely.…”

“…The addition of CNT not only contributes to photothermal conversion, but also enhances the mechanical properties of materials, which provides support for expanding the potential application scenarios for photothermal-driven LCEs. Cheng et al [ 89 ] reported a light-driven LCE film that could crawl along a hair ( Figure 10 d). The micro-structure of the hair’s surface provided different friction coefficients in different directions, allowing the soft robot to move along the hair in a single direction when stimulated by a manual scanning light beam.…”

“…One is friction control, which uses light to lock and slide between the legs and the other is a self-oscillating mode (Reprinted with permission from Ref. [ 89 ]. Copyright 2022, John Wiley and Sons).…”