New 3D printing approach means better biomedical, energy, robotics devices

The liquid crystalline elastomer structures printed by Devin Roach of the OSU College of Engineering and collaborators can crawl, fold and snap directly after printing.

"LCEs are basically soft motors," said Roach, assistant professor of mechanical engineering. "Since they're soft, unlike regular motors, they work great with our inherently soft bodies. So they can be used as implantable medical devices, for example, to deliver drugs at targeted locations, as stents for procedures in target areas, or as urethral implants that help with incontinence."

Liquid crystalline elastomers are lightly crosslinked polymer networks that are able to change shape significantly upon exposure to certain stimuli, like heat. They can be used to transfer thermal energy, such as from the sun or alternating currents, into mechanical energy that can be stored and used on demand. LCEs can also play a big role in the field of soft robotics, Roach added.

"Flexible robots incorporating LCEs could explore areas that are unsafe or unfit for humans to go," he said. "They have also been shown to have promise in aerospace as actuators for automated systems such as those for deep space grappling, radar deployment or extraterrestrial exploration."

Underpinning the functional utility of liquid crystalline elastomers is their blend of anisotropy and viscoelasticity, Roach said.

Anisotropy refers to the property of being directionally dependent, such as how wood is stronger along the grain than across it, and viscoelastic materials are both viscous -- like honey, which resists flow and deforms slowly under stress -- and elastic, returning to their original shape when the stress is removed, like rubber. Viscoeleastic materials slowly deform and gradually recover.

Liquid crystalline elastomers' shape-changing properties are dependent on the alignment of the molecules within the materials. Roach and collaborators at Harvard University, the University of Colorado, and Sandia and Lawrence Livermore national laboratories discovered a way to align the molecules using a magnetic field during a type of 3D printing called digital light processing.

Also known as additive manufacturing, 3D printing allows for the creation of objects one layer at a time. In digital light processing, light is used to harden liquid resin into solid shapes with precision. However, getting the elastomers' molecules aligned can be challenging.

"Aligning the molecules is the key to unlocking the LCEs' full potential and enabling their use in advanced, functional applications," Roach said.

Roach and the other researchers varied the strength of the magnetic field and studied how it and other factors, such as the thickness of each printed layer, affected molecular alignment. This enabled them to print complicated liquid crystalline elastomer shapes that change in specific ways when heated.

"Our work opens up new possibilities for creating advanced materials that respond to stimuli in useful manners, potentially leading to innovations in multiple fields," Roach said.

Supporting the study, which was published in Advanced Materials, were the National Science Foundation and the Air Force Office of Scientific Research.

In related research published in Advanced Engineering Materials, Roach led a team of Oregon State students and collaborators at Sandia, Lawrence Livermore and Navajo Technical University in exploring the mechanical damping potential of liquid crystalline elastomers.

Mechanical damping refers to reducing or dissipating the energy of vibrations or oscillations in mechanical systems, including automotive shock absorbers, seismic dampers that help protect buildings from earthquakes, and vibration dampers on bridges that minimize oscillations caused by wind or motor vehicles.

OSU students Adam Bischoff, Carter Bawcutt and Maksim Sorkin and the other researchers demonstrated that a fabrication method known as direct ink write 3D printing can produce mechanical damping devices that effectively dissipate energy across a wide range of loading rates.