Stretchy Circuits Extend Like Serpents

July 26, 2007 — Elastic circuits that stretch to more than twice their lengths could lead to new devices that can bend with a person's body — inside and out.

On the inside, the stretchy circuits could power everything from bladder implants that sense incontinence to brain electrodes that help treat epilepsy and depression. While on the outside, the elastic electronics could help advance fall-detecting bandages for the elderly, intelligent textiles that monitor health conditions, and new innovations, including stretchable thermometers and watches.

Many of these technologies are already possible in a rigid format, said Jan Vanfleteren, a professor at the University of Ghent in Belgium and also a R&D manager for the Interuniversity Microelectronics Center .

But how do you make the user accept the notion of strapping a hard, plastic sensor to their arms or implanting one in their skull?

"The answer is you should not make the user accept it at all. The user should hardly notice that the sensor is there. It should be very comfortable," said Vanfleteren.

And comfort means flexibility.

Vanfleteren and his team constructed the circuits by embedding gold wires and standard electronic components in stretchy silicone film. Instead of laying down the wires in a straight line, the researchers shaped them into a snakey pattern of repeating u's.

When they stretched the silicone, the wires elongated like an accordion to more then two times their original length.

"He has optimized the serpentine design to minimize the stress during deformation," said Stéphanie Lacour, research fellow with the Nanoscience Center at the University of Cambridge in the U.K.

Embedding the wires and components in silicone not only allows for elasticity but also for washability. The circuits are water-tight, which will help them withstand wetness inside a person's body or a washing machine.

Vanfleteren said he and his team developed the elastic circuits with commercialization in mind. The electronics were designed so that ultimately they could be made by manufacturers already printing rigid and flexible circuit boards.

But according to Lacour, industrial manufacturers are having issues handling plastics and getting them to change their processes is going to take time.

"It's going to take several years, maybe even ten, before we see stretchable moving to industry on a large production basis," she said.