Encoding many properties in one material via 3D printing

A category of artificial mushy supplies referred to as liquid crystal elastomers (LCEs) can change form in response to warmth, much like how muscle tissues contract and loosen up in response to alerts from the nervous system. 3D printing these supplies opens new avenues to purposes, starting from mushy robots and prosthetics to compression textiles.

Controlling the fabric’s properties requires squeezing this elastomer-forming ink by way of the nozzle of a 3D printer, which induces modifications to the ink’s inner construction and aligns inflexible constructing blocks referred to as mesogens on the molecular scale. Nevertheless, attaining particular, focused alignment, and ensuing properties, in these shape-morphing supplies has required intensive trial and error to completely optimize printing situations. Till now.

In a brand new examine, researchers on the Harvard John A. Paulson College of Engineering and Utilized Sciences (SEAS), Princeton College, Lawrence Livermore Nationwide Laboratory, and Brookhaven Nationwide Laboratory labored collectively to jot down a playbook for printing liquid crystal elastomers with predictable, controllable alignment, and therefore properties, each time.

By utilizing an X-ray characterization methodology through the printing course of that permits quantification of mesogen alignment on the microscale, the researchers have established a elementary framework to information their fast design and fabrication throughout a number of scales.

By tuning the microscale nozzle design, printing pace, and temperature, one can induce the specified molecular-scale alignment, which interprets into prescribed shape-morphing and mechanical conduct on the macroscale.

Published in Proceedings of the Nationwide Academy of Sciences, the examine’s senior creator is Jennifer Lewis, the Hansjörg Wyss Professor of Biologically Impressed Engineering at Harvard SEAS. Lewis’s lab has many years of expertise in molecular and nanoscale design of 3D printing inks for brand spanking new, practical supplies. The examine was co-led by former Harvard postdoctoral researcher Emily Davidson, now a school member at Princeton College, with experience within the design, nanoscale meeting, X-ray characterization, and 3D printing of soppy supplies.

Liquid crystal elastomers exhibit their finest shape-morphing and mechanical properties when particular person chains composed of liquid crystalline elements are aligned with one another. The researchers printed these liquid crystalline chains by way of effective nozzles, driving their flow-induced alignment.

“When this challenge started, we merely did not have an excellent understanding of exactly management liquid crystal alignment throughout extrusion-based 3D printing,” stated first creator Rodrigo Telles, a SEAS graduate scholar, Tutorial Cooperation Program scholar and collaborator with Lawrence Livermore Nationwide Laboratory. “But it’s their diploma of alignment that offers rise to various quantities of actuation and contraction when heated.”

To research alignment of molecules throughout printing, the researchers used different-shaped nozzles—tapered and hyperbolic. The nozzle form affected how the ink flowed out, which in flip managed molecular alignment. By various extrusion pace and nozzle form, they have been capable of create two sorts of filaments: one with an outer layer of well-aligned molecules surrounding a poorly aligned core, and one other with uniform alignment all through.

Their calculations and experiments confirmed that the distribution of circulate kind and pace contained in the nozzle decided the filament kind. Whereas there have been many elements that mattered, the researchers confirmed they might mix most of those right into a single parameter referred to as a Weissenberg quantity to explain how completely different printing situations align the molecules.

“Within the 3D printing group, most of us use a comparatively small variety of commercially accessible printheads. This examine confirmed us that it is necessary to concentrate to the small print of each nozzle geometry and circulate—and that we are able to exploit them to manage materials properties,” Davidson stated.

The staff labored with researchers at a wide-angle X-ray scattering beamline on the Division of Power’s Brookhaven Nationwide Laboratory to take detailed X-ray measurements throughout 3D printing. This methodology allowed them to look contained in the nozzles to visualise LCE alignment utilizing completely different nozzle geometries and circulate situations.

The X-ray measurements helped them decide the exact diploma of alignment of the liquid crystalline molecules at any given place inside the nozzles, offering a highway map for his or her flow-induced alignment that’s linked to tunable nozzle designs and printing parameters.

Amongst their outcomes was {that a} nozzle with a hyperbolic form created higher and extra uniform alignment than standard nozzles.

The work opens new avenues for fabricating LCE buildings with programmed form morphing and mechanics, to be used in purposes similar to adaptive buildings and synthetic muscle tissues.

“The flexibility to ‘see’ into liquid crystal elastomers and quantify their alignment on the microscale throughout printing by way of broad angle X-ray scattering measurements has offered a elementary framework of their processing-structure-property relationships for the primary time,” Lewis stated.