EPFL scientists have found a fast and simple way to make super-elastic, multi-material, high-performance fibres, which have already been used as sensors on robotic fingers and in clothing. This method opens the door to new kinds of smart textiles and medical implants, according to the team of scientists.

“It’s a whole new way of thinking about sensors,” they say. “The tiny fibres developed at EPFL are made of elastomer and can incorporate materials like electrodes and nanocomposite polymers. The fibres can detect even the slightest pressure and strain and can withstand deformation of close to 500% before recovering their initial shape. All that makes them perfect for applications in smart clothing and prostheses, and for creating artificial nerves for robots.”

The fibres were developed at EPFL’s Laboratory of Photonic Materials and fibre Devices (FIMAP), headed by Fabien Sorin at the School of Engineering. The scientists came up with a fast and easy method for embedding different kinds of microstructures in super-elastic fibres. For instance, by adding electrodes at strategic locations, they turned the fibres into ultra-sensitive sensors. What’s more, their method can be used to produce hundreds of metres of fibre in a short amount of time.

Heat, then stretch

To make the fibres, the scientists used a thermal drawing process, which is the standard process for optical- fibre manufacturing. They started by creating a macroscopic preform with the various fibre components arranged in a carefully designed 3D pattern. They then heated the preform and stretched it out, like melted plastic, to make fibres of a few hundred microns in diameter. And while this process stretched out the pattern of components lengthwise, it also contracted it crosswise, meaning the components’ relative positions stayed the same. The end result was a set of fibres with an extremely complicated microarchitecture and advanced properties.

“Until now, thermal drawing could be used to make only rigid fibres,” the university explains. “But Sorin and his team used it to make elastic fibres. With the help of a new criterion for selecting materials, they were able to identify some thermoplastic elastomers that have a high viscosity when heated. After the fibres are drawn, they can be stretched and deformed but they always return to their original shape.”

Rigid materials like nanocomposite polymers, metals and thermoplastics can be introduced into the fibres, as well as liquid metals that can be easily deformed. “For instance, we can add three strings of electrodes at the top of the fibres and one at the bottom. Different electrodes will come into contact depending on how the pressure is applied to the fibres. This will cause the electrodes to transmit a signal, which can then be read to determine exactly what type of stress the fibre is exposed to – such as compression or shear stress, for example,” said Fabien Sorin.

Artificial nerves for robots

Working in association with Professor Dr Oliver Brock (Robotics and Biology Laboratory, Technical University of Berlin), the scientists integrated their fibres into robotic fingers as artificial nerves. Whenever the fingers touch something, electrodes in the fibres transmit information about the robot’s tactile interaction with its environment. The research team also tested adding their fibres to large-mesh clothing to detect compression and stretching. “Our technology could be used to develop a touch keyboard that’s integrated directly into clothing, for instance” added Sorin.

The researchers say they see many other potential applications. Especially since the thermal drawing process can be easily tweaked for large-scale production. This is a real plus for the manufacturing sector. The textiles sector has already expressed interest in the new technology, and patents have been filed.

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