Researchers at Harvard University’s John A. Paulson School of Engineering and Applied Sciences have produced 3D printed filaments that are capable of bending, twisting, expanding, or contracting in response to temperature.

The behavior is modeled on biological structures such as elephant trunks, octopus tentacles, and plant tendrils, and the research builds on the rotational multimaterial 3D printing (RM-3DP) concept developed by Professor Jennifer A. Lewis.

The work, published in Proceedings of the National Academy of Sciences, was led by Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering, alongside professors L. Mahadevan and Joanna Aizenberg.

Harvard researchers print artificial muscle-like filaments that bend and twist on demand

RM-3DP uses a custom dual-channel nozzle to co-extrude two elastomers: an active liquid crystal elastomer (LCE), which contracts along its molecular alignment direction when heated above its nematic-to-isotropic transition temperature, and a passive acrylate elastomer that holds its shape regardless of temperature.

Rotating the nozzle during printing writes a helical molecular alignment into the LCE, programming the filament’s curvature and twist response during fabrication.

The two materials exhibited a 50-fold difference in elastic modulus, providing an additional design variable for tuning shape change, and under repeated thermal cycling between 25 °C and 175 °C, the filaments showed no observable degradation or interfacial delamination over 100 cycles.

Lead author Mustafa Abdelrahman described the conceptual origin of the work: “I saw this really beautiful [rotational 3D printing platform] and thought, ‘What if we plug in active materials and pattern them within the filament – can we drive shape change that way?’”

From filaments to functional structures

The team assembled the filaments into architected expanding and contracting lattices, and combining both types within a single structure produced flat lattices that morphed into dome or saddle shapes, closely matching computational predictions. 

As functional demonstrations, the researchers fabricated an active filter that opens and closes its apertures on thermal demand, and a pick-and-place gripper capable of simultaneously lifting and transferring multiple objects, which was a departure from most soft grippers, which handle one object at a time. 

“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.

Lewis framed the industrial relevance of the work: “This filament design and printing framework could accelerate the transition of artificial muscle-like materials from the lab to real-world technologies.”