Stretchable circuits for wearable e-skin

November 09, 2020 // By Nick Flaherty
Stretchable circuits for wearable e-skin
Researchers at the University of Colorado Boulder are developing a stretchable, self-healing electronic circuit that sticks onto human skin and can be easily recycled.

The self-healing e-skin developed by Jianliang Xiao and Wei Zhang can, measuring the body temperature of users to tracking daily step counts. It is also reconfigurable so that it can be shaped to fit anywhere on the body.

"If you want to wear this like a watch, you can put it around your wrist," said Xiao, an associate professor in the Paul M. Rady Department of Mechanical Engineering at CU Boulder. "If you want to wear this like a necklace, you can put it on your neck."

"Smart watches are functionally nice, but they're always a big chunk of metal on a band," said Zhang, a professor in the Department of Chemistry. "If we want a truly wearable device, ideally it will be a thin film that can comfortably fit onto your body."

Xiao and his team used screen printing to create a network of liquid metal wires. They then sandwich those circuits in between two thin films made out of a highly flexible and self-healing material called polyimine.

The design uses a MCP9700 temperature sensor from Microchip Technology, an ADXL335 triaxial accelerometer from Analog Devices and a ECG sensor using the AD8505 from Analog Devices and resistors from Bourns. The resulting device is a little thicker than a sticking plaster and can be applied to skin with heat. It can also stretch by 60 percent in any direction without disrupting the electronics.

"It's really stretchy, which enables a lot of possibilities that weren't an option before," said Xiao.

The e-skin is also highly resilient. If you slice a patch of electronic skin, Zhang said, all you have to do is pinch the broken areas together. Within a few minutes, the bonds that hold together the polyimine material will begin to reform. Within 13 minutes, the damage will be almost entirely undetectable.

"Those bonds help to form a network across the cut. They then begin to grow together," Zhang said.

The e-skin uses sensors from Microchip and Analog Devices

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