Flexible fibre actuator converts electricity into motion

Researchers from Tohoku University have developed an ultra-fine ‘soft yarn’ actuator fibre that can bend, contract and produce 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 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 at Tohoku University developed an actuator made from a flexible polymer fibre. 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 researchers adapted a manufacturing technique originally developed for optical fibre production known as thermal drawing. Using an optimised drawing process, the team fabricated actuator fibres roughly the thickness of a human hair while preserving their mechanical softness and flexibility.

The new actuator was developed using 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 fibres that respond to voltage by bending, contracting and generating undulating movements in three dimensions.

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

The fibre’s thread-like shape is important for practical applications; unlike flat or bulky actuators, the new device can be wound into spirals, 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. 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 optimising electrode materials and refining the internal structure of the fibre. They also aim to integrate additional capabilities, such as sensing functions and fluidic channels, into the same fibre platform. Ultimately, the researchers hope to develop multifunctional fibres that can sense their environment and move in response, enabling a new generation of gentle, body-conforming robotic technologies.

Top image caption: Electrically driven ‘soft yarn’ (soft fibre actuator) realised by thermal drawing. Image credit: Tohoku University.