Bioinspired Artificial Muscle Filaments Bend And Twist With Temperature Changes

Nature is replete pinch slender filaments that crook and coil – from climbing grape vines, to folded proteins, to elephant trunks that tin prime up a peanut but besides return down a tree. 

Harvard scientists seeking to endow synthetic materials pinch this type of nature-inspired beingness power person developed a 3D printing strategy that turns soft, hair-like filaments into programmable "artificial muscles" that bend, twist, expand, aliases statement erstwhile heated aliases cooled. It's an innovative measurement toward recreating nan complexity of biologic muscles, which dwell of bundles of fibers that activity together to nutrient intricate motions. 

The breakthrough is from nan laboratory of Jennifer Lewis, nan Hansjorg Wyss Professor of Biologically Inspired Engineering successful nan John A. Paulson School of Engineering and Applied Sciences (SEAS), and described in Proceedings of nan National Academy of Sciences by first writer and postdoctoral interrogator Mustafa Abdelrahman and colleagues. 

Rotational multimaterial 3D printing

In their study, nan researchers utilized a method developed successful nan Lewis laboratory called rotational multimaterial 3D printing to people unsocial filaments consisting of components that alteration style and components that don't, aliases what they telephone progressive and passive materials. Their progressive worldly is simply a liquid crystal elastomer, a typical type of polymer that has attracted investigation liking arsenic a campaigner for artificial musculus because it "contracts" on a preferred guidance erstwhile heated supra a modulation temperature. 

Their passive worldly is simply a soft elastomer that maintains its style contempt somesthesia shifts and whose stiffness acts arsenic a mechanical mobility guide. By extruding some materials broadside by broadside done a rotating nozzle, nan researchers tin spot progressive and passive regions precisely wherever they want them astir nan full filament's cross-section. 

Because nan progressive liquid crystal elastomer shrinks on its soul molecular alignment guidance erstwhile heated, and nan passive worldly does not, moreover a elemental bilayer filament bends arsenic 1 broadside shortens and nan different resists. Rotating nan nozzle arsenic it prints efficaciously "writes" a helical alignment of nan progressive molecules into nan filament.

The consequence is simply a filament whose earthy curvature and twist erstwhile activated are pre‑programmed during printing - nary assembly of aggregate layers aliases mechanical post-processing required. 

Before joining nan Lewis lab, Abdelrahman had created sheets of liquid crystal elastomers utilizing much analyzable methods for drafting retired their properties and was looking to research much customizable processes. "I saw this really beautiful [rotational 3D printing platform] and thought, 'What if we plug successful progressive materials and shape them wrong nan filament – tin we thrust style alteration that way?'" 

To validate and foretell nan materials' behavior, nan squad worked intimately pinch Professor L. Mahadevan, whose group specializes successful nan mechanics of earthy structures, and Professor Joanna Aizenberg, whose laboratory helped qualify nan molecular alignment of nan liquid crystal elastomers utilizing X‑ray scattering measurements performed astatine Brookhaven National Laboratory.

Demonstrations of analyzable structures

Once nan researchers could provably programme nan style alteration of a azygous filament, they utilized those filaments arsenic building blocks for much complex, architected structures.

They printed sinusoidal filaments - wavy strands that initially look identical but deform very otherwise depending connected wherever nan progressive liquid crystal elastomer is placed. When nan liquid crystal elastomer is printed connected the outside of nan wave's curvature, heating causes nan filament to straighten and expand. But erstwhile nan progressive elastomer is connected the inside, nan aforesaid thermal stimulus makes nan filament shrink and contract.

By weaving these portion cells into level lattices, nan squad demonstrated nan imaginable of progressive filters - lattices that, erstwhile heated, unfastened to fto spherical particles walk through, and erstwhile cooled, statement to trap aliases support them. They besides made a benignant of pick‑and‑place gripper - free‑standing lattices that tin beryllium lowered onto aggregate rods, heated to grip and assistance them, past cooled to merchandise nan rods. 

In 1 experiment, a lattice printed pinch alternating expanding and contracting regions shape-shifted into a dome‑like style erstwhile heated successful an lipid bath, intimately matching nan shape predicted by simulations.

The squad is exploring scaling nan technology. With custom‑fabricated nozzles and cautiously tuned inks, they person already printed filaments arsenic mini arsenic astir 100 microns successful diameter and spot opportunities to spell smaller.

"In position of scalability, you could create much analyzable nozzles that merge pinch different materials successful nan early – like, having a liquid metallic transmission to alteration actuation, aliases integrating different functionality," said postgraduate student and co-author Jackson Wilt. 

While liquid crystal elastomers are only opening to look successful business products, they are being actively explored for soft robotics, power damping, and biomedical devices. 

"This filament creation and printing model could accelerate nan modulation of artificial muscle-like materials from nan laboratory to real-world technologies," Lewis said. 

Potential applications see reconfigurable soft robotic grippers that tin mildly manipulate galore objects astatine once; progressive filters and valves whose porosity and travel pathways tin beryllium tuned pinch temperature; and entangled, injectable filaments that could fastener together successful spot to shape porous, high‑surface‑area structures - useful, for example, successful biomedical contexts wherever accelerated clotting of biologic insubstantial is needed.

"Rotational 3D printing of active-passive filaments and lattices pinch programmable style morphing" was additionally co-authored by Yeonsu Jung, Rodrigo Telles, Gurminder K. Paink, and Natalie M. Larson. Federal support for nan investigation came from nan National Science Foundation done nan Harvard MRSEC (DMR-2011754) and nan ARO MURI programme (W911NF-17-1-03; W911NF-22-1-0219). Some activity was performed astatine nan Harvard University Center for Nanoscale Systems, supported by nan NSF nether grant No. ECCS-2025158. Other activity took spot astatine nan National Synchrotron Light Source II, operated by nan DOE Office of Science by Brookhaven National Laboratory nether statement No. DE-SC0012704.