From Light-Powered Motors, to Micro-Grippers, to Crawling Caterpillars, Snails and Beyond—Light-Responsive Oriented Polymers in Action

Abstract

“How would you build a robot, the size of a bacteria, powered by light, that would swim towards the light source, escape from it, or could be controlled by means of different light colors, intensities or polarizations?” This was the question that Professor Diederik Wiersma asked PW on a sunny spring day in 2012, when they first met at LENS—the European Laboratory of Nonlinear Spectroscopy—in Sesto Fiorentino, just outside Florence in northern Italy. It was not just a vague question, as Prof. Wiersma, then the LENS director and leader of one of its research groups, already had an idea (and an ERC grant) about how to actually make such micro-robots, using a class of light-responsive oriented polymers, liquid crystal elastomers (LCEs), combined with the most advanced fabrication technique—two-photon 3D laser photolithography. Indeed, over the next few years, the LCE technology, successfully married with the so-called direct laser writing at LENS, resulted in a 60 micrometer long walker developed in Prof. Wiersma’s group (as, surprisingly, walking at that stage proved to be easier than swimming). After completing his post-doc at LENS, PW returned to his home Faculty of Physics at the University of Warsaw, and started experimenting with LCE, both in micrometer and millimeter scales, in his newly established Photonic Nanostructure Facility. This paper is a review of how the ideas of using light-powered soft actuators in micromechanics and micro-robotics have been evolving in Warsaw over the last decade and what the outcomes have been so far.

Liquid crystal elastomer actuators and sensors: Glimpses of the past, the present and perhaps the future

“…I then recount, in Section 3, what I believe are the key events from the development that has led to our current understanding of LCE physics and chemistry as well as today's access to materials of relevance. I try to balance a chronological account with a logical structuring by themes, to add an aspect that I believe was less prominent in previous reviews of the field, some examples listed here (Ikeda et al, 2007;Hager et al, 2015;White and Broer, 2015;Pilz da Cunha et al, 2020;Hussain et al, 2021;Guan et al, 2022;Herbert et al, 2022;Lugger et al, 2022;Rogóz et al, 2022;Saed et al, 2022;van Raak and Broer, 2022;Wang et al, 2022a,b;Zhang et al, 2022;Zhao et al, 2022;Wu et al, 2023b). Many recent reviews provide good overviews of the newest advances, generally dealing more with device operation than the fundamental physics, or they focus on a specific challenge, like control of alignment or reprogrammability.…”