Optical Pliers Made with Smart, Flexible Material Operate Remotely

Liquid crystal elastomer (LCE) technology was applied to practical use by a group of researchers who used this material to demonstrate a miniaturized gripping tool grown on optical fibers. Scientists from the University of Warsaw worked with colleagues from the AGH University of Science and Technology in Krakow to build the miniaturized “optical pliers” using LCE microstructures.

The device was built by growing two bending “jaws” on the tips of hair-size optical fibers. The 200-μm grippers are controlled remotely with green light delivered through the fibers. The light energy is absorbed and directly converted to activate the jaws of the gripper.

LCEs are smart materials that can reversibly change shape under illumination. In a prototype of the miniaturized optical pliers, the scientists combined the light-powered LCEs with a new method of fabricating micrometer-scale structures.

The optical pliers next to the mandibles of a Formica polyctena ant for comparison (composite scanning electron microscope image with added colors). The two jaws (red) close when light is sent through the optical fibers (light blue) that have the diameter of 125 μm, comparable to the diameter of a human hair. Courtesy of UW Physics.

When the scientists sent UV light through the optical fiber, a cone-shaped microstructure grew at the fiber tip. The light-induced mechanical response of this microstructure depended on the orientation of molecules inside the elastomer element. The structure’s response could be controlled to achieve bending or contracting microactuators.

Mechanical grippers powered by electric, pneumatic, hydraulic, or piezoelectric servos are well suited for gripping at larger scales, but their complexity and need for force transmission prevent their miniaturization and remote control in tight spaces. The “optical pliers” from the Warsaw team are operated using visible light energy supplied through the fibers, with no force transmission.

By delivering UV light to trigger polymerization via a micrometer-size fiber core, structures of similar size could be made without using microfabrication technology such as laser photolithography, the researchers said. The elastomer growth technique could be used for different micrometer-scale, remotely controlled functional structures and could provide the building blocks for an optically powered micro-toolbox.

The research was published in Advanced Materials (www.doi.org/10.1002/adma.202002779).