Soft Fibers that Move with Electricity

Electrically driven 'soft yarn' (soft fiber actuator) realized by thermal drawing.
Image Credit: ©Tohoku University

Scientific Frontline: Extended "At a Glance" Summary: Soft Fibers that Move with Electricity

The Core Concept: The soft fiber actuator is an ultrafine, electrically driven "soft yarn" made from flexible polymer capable of bending, contracting, and producing complex three-dimensional movements upon the application of an electrical voltage.

Key Distinction/Mechanism: Unlike conventional metallic actuators (such as shape-memory alloys) that are relatively stiff and require complex heating or magnetic fields for activation, this technology uses a flexible dielectric elastomer. When an electric field is applied, electrostatic forces induce physical deformation, allowing the thread-like material to generate complex motions while maintaining a soft, rubber-like feel that can be knitted or woven into textiles.

Major Frameworks/Components: 

• Thermoplastic Polyurethane: The highly flexible polymer material acting as the core dielectric elastomer.
• Thermal Drawing: A high-precision manufacturing technique, originally designed for optical fiber production, adapted to fabricate functional soft fibers around the thickness of a human hair.
• Dielectric Elastomer Actuation (DEA): The underlying operational principle where applied voltage induces electrostatic forces between electrodes, causing the soft polymer to deform and contract.

Branch of Science: Materials Science, Soft Robotics, Biomedical Engineering, and Polymer Chemistry.

Future Application: The thread-like fibers can be wound into spirals, woven into fabrics, or integrated into complex three-dimensional wearable robotics and medical assistive devices. Future iterations aim to integrate sensing functions and fluidic channels directly into the fiber platform.

Why It Matters: The high compliance and thinness of these soft actuators resolve the rigidity and safety issues associated with traditional robotic components. This paves the way for a new generation of gentle, body-conforming wearable technologies capable of safe, close-proximity interaction with humans.

Operating principle and displacement response of the electrically driven "soft yarn" (soft fiber actuator). (A) Voltage induces electrostatic forces between electrodes, causing deformation. (B) Measurement setup schematic. (C) Tip displacement under AC voltage shows stable periodic motion synchronized with the input.
Image Credit: ©Tohoku University

Researchers at Tohoku University, working with international collaborators in France, have developed an ultrafine "soft yarn" actuator fiber capable of bending, contracting, and producing complex three-dimensional movements when electricity is applied. The technology offers a new pathway for building safer soft robots and body-conforming wearable devices designed to interact closely with people.

Soft actuators - materials that convert electrical energy into motion - are a key component in next-generation technologies such as soft robotics, medical devices, and wearable assistive systems. However, many conventional actuators rely on metallic materials such as shape-memory alloys. These materials are often relatively stiff, provide limited degrees of freedom, and typically require complex activation methods involving heating or magnetic fields.

To overcome these challenges, an international research team led by Associate Professor Yuanyuan Guo of the Frontier Research Institute for Interdisciplinary Sciences and the Graduate School of Biomedical Engineering at Tohoku University, together with undergraduate researcher Yuto Akimoto, developed a new actuator made from a flexible polymer fiber. The work was carried out in collaboration with researchers from the MatéIS Laboratory at INSA Lyon in France and the ELyTMaX Japan-France Joint Laboratory.

The team adapted a manufacturing technique originally developed for optical fiber production known as thermal drawing. Using an optimized drawing process, the researchers fabricated actuator fibers roughly the thickness of a human hair while preserving their mechanical softness and flexibility.

Spiral-Shaped DEA Fiber with Electrically Driven Swirling Motion 

Video Credit: Biofibertronics

At the heart of the new actuator is thermoplastic polyurethane, a highly flexible material that can function as a dielectric elastomer - meaning it deforms when an electric field is applied. By identifying processing conditions compatible with thermal drawing, the team successfully produced fibers that respond to voltage by bending, contracting, and generating undulating movements in three dimensions.

"By combining fiber manufacturing techniques with soft electroactive materials, we were able to create one of the thinnest and softest electrically driven actuators reported in fiber form," said Yuanyuan Guo. "Because the actuator behaves like a thread, it can be easily integrated into textiles and flexible structures."

The fiber's thread-like shape is particularly important for practical applications. Unlike flat or bulky actuators, the new device can be wound into spirals (see video below), knitted into fabrics, or woven into complex three-dimensional structures. This allows the actuator to generate motions that are difficult to achieve with conventional planar systems while maintaining a soft, rubber-like mechanical feel suitable for direct contact with the human body.

Such characteristics could make the technology especially useful for wearable robotics, assistive devices, and other systems designed to safely interact with people. Because the actuator is soft and highly compliant, it can produce controlled motion without rigid components that might otherwise cause discomfort or safety concerns.

Looking ahead, the researchers plan to improve the actuator's performance by optimizing electrode materials and refining the internal structure of the fiber. They also aim to integrate additional capabilities - such as sensing functions and fluidic channels - into the same fiber platform. Ultimately, the team hopes to develop multifunctional fibers that can both sense their environment and move in response, enabling a new generation of gentle, body-conforming robotic technologies.

Published in journal: ACS Omega

Title: Thermally Drawn Soft Dielectric Elastomer Actuator Fibers

Authors: Yuto Akimoto, Gildas Coativy, Jean-Yves Cavaillé, Jérôme Adrien, Eric Maire, and Yuanyuan Guo

Source/Credit: Tohoku University

Reference Number: ms031026_01

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