Alignment-Flipping Liquid-Crystal Ink Delivers 3D-Printable Programmable, Flexible Soft Actuators

Researchers from Pusan National University, the Oak Ridge National Laboratory (ORNL), and the University of Maryland have come up with a new way to 3D print more flexible soft actuators — using a "smectic liquid-crystal elastomer (LCE) ink" capable of flipping molecular alignment during the printing process.

"Our work provides the first demonstration of switching molecular alignment between two orthogonal directions using a single 3D-printable smectic LCE ink," claims project lead Suk-kyun Ahn of the team's project, "simply by tuning the printing speed and temperature. Over the next 5–10 years, this work could help 3D-printed x-x-objects go beyond just holding a fixed shape. Instead, they could actively change shape and carry out specific functions."

A traditional 3D-printed object is relatively static: it's either solid or, at best, flexible when printed in a material like TPU. You can combine static shapes to create moving objects, as in articulated fidget toys, but the solids themselves remain stubbornly single-shaped.

Using the team's new smectic ink, meaning a liquid crystal where molecules are aligned perpendicular to the plane of the layers, it's possible to 3D print objects that change shape when heated or cooled — and to decide whether that means they expand or contract when heated print-by-print.

By adjusting the print speed or temperature, the molecular orientation of the ink can be flipped: oriented one way and the material expands when heated, while if it's oriented the other way it contracts. As print speed and temperature can be changed on-the-fly, that means it's possible to print objects that grow in some places and shrink in others — creating surprisingly complicated temperature-driven soft actuators.

"Potential real-life applications include soft robotic actuators and artificial muscles, reconfigurable surfaces for haptic displays, and adaptive textures that regulate aerodynamic drag," says Ahn, a professor in Pusan National University's School of Chemical Engineering and the Department of Polymer Science and Engineering. The researchers also highlight use-cases including shape-changing wearables and minimally-invasive medical tools.

The team's paper is in press now for the journal Nature Communications, with an unedited version of the manuscript openly provided under early-access terms.