Crawling by means of the traveling deformation of a soft body is a widespread mode of locomotion in nature—animals across scales, from microscopic nematodes to earthworms to gastropods, use it to move around challenging terrestrial environments. Snails, in particular, use mucus—a slippery, aqueous secretion—to enhance the interaction between their ventral foot and the contact surface. In this study, a millimeter‐scale soft crawling robot is demonstrated that uses a similar mechanism to move efficiently in a variety of configurations: on horizontal, vertical, as well as upside‐down surfaces; on smooth and rough surfaces; and through obstacles comparable in size to its dimensions. The traveling deformation of the robot soft body is generated via a local light‐induced phase transition in a liquid crystal elastomer and resembles the pedal waves of terrestrial gastropods. This work offers a new approach to micro‐engineering with smart materials as well as a tool to better understand this mode of locomotion in nature.
The ability to grip and handle small objects, from sub‐millimeter electronic components to single‐micrometer living cells, is vital for numerous ever‐shrinking technologies. Mechanical grippers, powered by electric, pneumatic, hydraulic or piezoelectric servos, are well suited for the job at larger scales, but their complexity and need for force transmission prevent their miniaturization and remote control in tight spaces. Using liquid crystal elastomer microstructures that can change shape quickly and reversibly in response to light, a light‐powered gripping tool—optical pliers—is built by growing two bending jaws on the tips of optical fibers. By delivering UV light to trigger polymerization via a micrometer‐size fiber core, structures of similar size can be made without resorting to any microfabrication technology, such as laser photolithography. The tool is operated using visible light energy supplied through the fibers, with no force transmission. The elastomer growth technique readily offers micrometer‐scale, remotely controlled functional structures with different modes of actuation as building blocks for the microtoolbox.
The
photomechanical response of liquid crystal polymer networks (LCNs)
can be used to directly convert light energy into different forms
of mechanical energy. In this study, we demonstrate how a traveling
deformation, induced in a liquid crystal polymer ring by a spatially
modulated laser beam, can be used to drive the ring (the rotor) to
rotate around a stationary element (the stator), thus forming a light-powered
micromotor. The photomechanical response of the polymer film is modeled
numerically, different LCN molecular configurations are studied, and
the performance of a 5.5 mm diameter motor is characterized.
Laboratory procedures are often considered so unique that automating them is not economically justified – time and resources invested in designing, building and calibrating the machines are unlikely to pay off. This is particularly true if cheap labour force (technicians or students) is available. Yet, with increasing availability and dropping prices of many off-the-shelf components such as motorised stages, grippers, light sources (LEDs and lasers), detectors (high resolution, fast cameras), as well as user-friendly programmable microprocessors, many of the repeatable tasks may soon be within reach of either custom-built or universal lab robots. Building on our previous work on fabrication, characterization and applications of light-responsive liquid crystal elastomers (LCEs) in micro-robotics and micro-mechanics, in this paper we present a robotic workstation that can make LCE films with arbitrary molecular orientation. Based on a commercial 3D printer, the RoboLEC (Robot for LCE fabrication) performs precision component handling, structured light illumination, liquid dispensing and UV-triggered polymerization, within a four-hour-long procedure. Thus fabricated films with patterned molecular orientation are compared to the same, but handmade, structures.
Front Cover: In article number 1900279, Piotr Wasylczyk and co‐workers demonstrate a light‐powered, soft snail robot capable of adhesive locomotion. The traveling deformation used for the robot propulsion is generated by photo‐mechanical response in a liquid crystal elastomer (LCE) continuous actuator. Crawling on various surfaces and in many configurations is presented, up to the extreme of an upside‐down glass plate.
“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.
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