Researchers have developed a 3D printing strategy to create programmable artificial muscles. 

Harvard’s SEAS and the Wyss Institute researchers drew inspiration from slender, coiling filaments found in nature, such as grapevines and elephant trunks.

This enabled soft synthetic materials to perform complex movements — such as bending, twisting, and contracting — in response to temperature changes.

Rotational multimaterial 3D printing

Standard 3D printing is a linear affair. However, the Lewis lab used a technique called rotational multimaterial 3D printing to create filaments that mimic biological muscle movement. 

Interestingly, the system has a spinning nozzle that extrudes and pumps two different materials through this rotating head. One is “active,” and the other is “passive,” both of which can create a helical internal structure. 

The active material, a liquid crystal elastomer (LCE), is a key polymer that physically shrinks when heated. On the other hand, the passive material (a soft elastomer) remains stationary.

When heat is applied to the finished filament, the internal tug-of-war between the shrinking LCE and the rigid passive elastomer forces the entire strand to bend, twist, or coil. 

This process creates a helical alignment that dictates how the strand will bend or twist; when heated, the active material contracts against the passive guide’s resistance, triggering a predetermined, complex shape change without manual assembly. 

“The result is a filament whose natural curvature and twist when activated are pre-programmed during printing—no assembly of multiple layers or mechanical post-processing required. Rotation rate during printing has a strong impact on how individual filaments shape-morph upon heating,” the team noted.

Use in soft robotics

Collaborative efforts with mechanics and molecular alignment experts enabled the validation and prediction of these materials’ behaviors through advanced X-ray scattering.

With single-filament programming established, these strands served as building blocks for complex, architected structures, such as sinusoidal filaments. 

Interestingly, researchers developed functional prototypes, such as temperature-sensitive active filters and multi-object grippers.

The movement of these structures is determined by the position of the active elastomer: placing it on the outer curve allows the lattice to expand and open, while placing it on the inner curve causes it to contract and grip.

This programmable architecture enables the transition from simple strands to complex devices capable of precisely trapping particles or manipulating multiple items at once. 

After this initial development, the scalability efforts are currently focused on miniaturization — with custom nozzles and specialized inks already producing filaments as thin as 100 microns.

Future developments aim to reduce this size even further while integrating multi-functional components.

“In terms of scalability, you could create more complex nozzles that integrate with other materials in the future—like, having a liquid metal channel to enable actuation, or integrating other functionality,” said graduate student and co-author Jackson Wilt.

Although liquid crystal elastomers are still in the early stages of industrial adoption, this new printing framework is expected to move artificial muscles into practical applications such as soft robotics, energy damping, and biomedicine.

The technology could enable the creation of reconfigurable grippers for delicate multi-object manipulation and temperature-tunable valves for fluid control. Most notably, the potential for injectable, self-locking filaments offers a promising solution for biomedical needs.

The findings were published in the journal Proceedings of the National Academy of Sciences.