Liquid Metal Enables Highly Stretchable Sensors for Next-Generation Wearables

A new fiber sensor maintains high sensitivity even when stretched to over 10 times its original length, showing potential applications in smart textiles, physical rehabilitation equipment, and soft robotics. 

The term 'liquid metal' might evoke thoughts of something dangerous, such as mercury or molten steel.

However, at the Laboratory of Photonic Materials and Fiber Devices (FIMAP) within EPFL’s School of Engineering, it refers to a combination of indium and gallium that is non-toxic, stays in a liquid state at room temperature, and holds significant potential for the advancement of electronic fibers intended for wearables and robotic sensors. The team's study was recently published in Nature Electronics.

Unfortunately, as Fabien Sorin, the head of FIMAP, explains, liquid metals present significant processing challenges, particularly in the production of electronic fibers that achieve both high and stable conductivity, as well as stretchability. However, the laboratory has successfully addressed this issue through a method known as thermal drawing, a technique that is conventionally employed in the fabrication of fiber optics.

We have integrated thermal drawing into a greatly simplified process for producing fiber sensors with finely tailored electronic properties, making them promising candidates for smart textiles for sport and health monitoring applications.

Fabien Sorin, Head, Laboratory of Photonic Materials and Fiber Devices (FIMAP), EPFL

The team employed the method to create an intelligent knee brace capable of tracking a user's movements and joint functionality during physical activity.

Simple, Sensitive, Stretchable

The thermal drawing process begins with the creation of a preform - a macroscopic representation of the electronic fiber - which consists of liquid metal components carefully organized in a three-dimensional configuration.

The preform is subjected to heating and elongation, like melted plastic, resulting in fibers with diameters ranging from a few hundred microns to millimeters that preserve the identical three-dimensional pattern.

PhD student and primary author Stella Laperrousaz states that this pattern is crucial to the team's innovation, as it enables the researchers to regulate which sections of a single fiber are active (electrically conductive) or inactive (insulating).

When the liquid metal is mixed with a soft elastomer matrix, it forms many small droplets. The process of heating and stretching the preform breaks these droplets and activates the liquid metal. This means that we can finely tune the functionality of a single fiber by controlling which areas become active through the shear stress caused by the preform stretching process.

Stella Laperrousaz, Ph.D. Student and Study Primary Author, EPFL 

Research demonstrated that the fibers developed by the team maintained exceptional sensitivity even when stretched to more than 10 times their initial length. This technique, therefore, has a considerable edge over alternative methods that find it challenging to achieve a balance between electrical performance, stretchability, and ease of processing.

A Smart Knee Brace

As a demonstration of their concept, the researchers successfully incorporated their electronic fibers into a flexible knee brace and documented the device's functionality as a participant walked, ran, squatted, and jumped. The brace consistently tracked the bending angle of the user's knee and was capable of precisely reconstructing their gait while running.

Sorin adds that this fiber could be used to monitor motion and detect anomalies in other joints, like the ankles, shoulders, or wrists, due to its ease of integration and potential scalability.

“Conventional electronic devices can be too fragile or too rigid to be integrated into textiles, but our fiber could be integrated into meters – or even kilometers – of fabric with sufficient scale-up, which is what we are working on next. Such fabric could then be used to produce wearables, soft prostheses, or sensors for robotic limbs,” said Sorin.

Journal Reference:

Laperrousaz, S., et al. (2025) Electronic fibres via the thermal drawing of liquid-metal-embedded elastomers. Nature Electronics. doi.org/10.1038/s41928-025-01485-0