Researchers from EPFL have developed conductive tracks that they say are almost as flexible as rubber and can be stretched up to four times their original length and in all directions. The team claims the electronics can also be stretched a million times without cracking or interrupting their conductivity.

Both solid and flexible, the researchers say this metallic and partially liquid film could be used to make circuits that can be twisted and stretched - for applications such as artificial skin on prosthetics or robotic machines. It could also be integrated into fabric and used in connected clothing. And because it follows the shape and movements of the human body, it could be used for sensors designed to monitor particular biological functions.

Owing to the high surface tension of some of these liquid metals, experiments conducted so far have produced relatively thick structures. "Using the deposition and structuring methods that we developed, it's possible to make tracks that are very narrow - several hundredths of a nanometre thick - and very reliable," explained Stéphanie Lacour, who runs the Laboratory for Soft Bioelectronic Interfaces (LSBI).

Apart from their unique fabrication technique, the researchers' secret lies in the choice of ingredients, an alloy of gold and gallium. Hadrien Michaud, a PhD student at LSBI, said: “The two materials are intertwined and they form a continuous film that maintains its conductivity even when the material is stretch to four times its length.”

Arthur Hirsch, another PhD student at LSBI added: "Not only does gallium possess good electrical properties, but it also has a low melting point, around 30°C, and, thanks to the process known as supercooling, it remains liquid at room temperature." The layer of gold ensures the gallium remains homogeneous, preventing it from separating into droplets when it comes into contact with the polymer, which would ruin its conductivity.