Researchers at the Swiss Federal Institute of Technology Lausanne (EPFL) have developed an extraordinary new electronic fiber that can stretch to more than ten times its original length while still working perfectly.
This innovation could open the door to a new generation of smart clothing, rehabilitation devices, and soft robots that can sense movement and pressure just like human skin.
The secret behind this invention is liquid metal—but not the kind that sounds dangerous or futuristic, like mercury or molten steel.
Instead, the EPFL team used a harmless mix of indium and gallium, which stays liquid at room temperature and conducts electricity extremely well.
The challenge, however, was turning this slippery liquid metal into something that could be built into soft, flexible fibers without losing its conductivity or falling apart when stretched.
That’s where Fabien Sorin and his team at the Laboratory of Photonic Materials and Fiber Devices (FIMAP) came in.
Using a technique called thermal drawing, they created a stretchable electronic fiber that combines strength, flexibility, and stable electrical performance. Thermal drawing is a process normally used to make fiber-optic cables, but the researchers adapted it to produce complex, electronic fibers.
Their study, recently published in Nature Electronics, showcases how the new technique can transform wearable technology and robotics.
To make the fiber, the team began by building a large-scale model, known as a preform, which contains the same structure as the final fiber but on a bigger scale.
Inside the preform, the liquid metal is carefully arranged in a three-dimensional pattern.
The preform is then heated and stretched—like soft plastic being pulled into thin strands—while keeping the same internal design.
The result is a long, hair-thin fiber that contains both conductive and insulating regions, depending on where the liquid metal droplets are activated.
Ph.D. student Stella Laperrousaz, the study’s first author, explained that when the liquid metal is combined with a soft, rubbery material (an elastomer), it forms many small droplets. During the stretching process, these droplets break apart and connect, allowing electricity to flow through specific regions of the fiber.
This clever control over which parts of the fiber conduct electricity makes it possible to design fibers that can sense bending, pressure, or stretching.
Tests showed that the fiber remained highly sensitive even when stretched to more than ten times its length—a huge improvement over other stretchable materials, which often lose their electrical performance when stretched.
To demonstrate the technology, the researchers built a smart knee brace by weaving their electronic fibers into soft fabric.
When a person walked, ran, squatted, or jumped, the brace accurately tracked the bending of their knee and could even reconstruct their running gait. This kind of precision could make the fiber ideal for use in physical therapy, helping patients monitor joint recovery or detect abnormal movement patterns.
According to Sorin, the technology is also scalable. That means the fibers could be produced in large quantities and woven into entire garments, prosthetic devices, or even robotic skins. “Conventional electronics are often too rigid or fragile for textiles,” he said, “but our fiber can be integrated into meters—or even kilometers—of fabric.”
In the future, these stretchable, electronic fibers could power everything from smart sportswear that monitors performance to soft robots that sense their environment. With this breakthrough, the boundary between fabric and technology is becoming thinner—and smarter—than ever.
Source: EPFL.
The FIMAP Lab’s smart knee brace. Credit: EPFL/Hugo Masson CC BY SA.
