'Building up' stretchable electronics to be as multipurpose as your smartphone

By stacking and connecting layers of stretchable circuits on top of one another, engineers have developed an approach to build soft, pliable "3D stretchable electronics" that can pack a lot of functions while staying thin and small in size. The work is published in the Aug. 13 issue of Nature Electronics.

As a proof of concept, a team led by the University of California San Diego has built a stretchable electronic patch that can be worn on the skin like a bandage and used to wirelessly monitor a variety of physical and electrical signals, from respiration, to body motion, to temperature, to eye movement, to heart and brain activity. The device, which is as small and thick as a U.S. dollar coin, can also be used to wirelessly control a robotic arm.

"Our vision is to make 3D stretchable electronics that are as multifunctional and high-performing as today's rigid electronics," said senior author Sheng Xu, a professor in the Department of NanoEngineering and the Center for Wearable Sensors, both at the UC San Diego Jacobs School of Engineering.

Xu was named among MIT Technology Review's 35 Innovators Under 35 list in 2018 for his work in this area.

To take stretchable electronics to the next level, Xu and his colleagues are building upwards rather than outwards. "Rigid electronics can offer a lot of functionality on a small footprint--they can easily be manufactured with as many as 50 layers of circuits that are all intricately connected, with a lot of chips and components packed densely inside. Our goal is to achieve that with stretchable electronics," said Xu.

The new device developed in this study consists of four layers of interconnected stretchable, flexible circuit boards. Each layer is built on a silicone elastomer substrate patterned with what's called an "island-bridge" design. Each "island" is a small, rigid electronic part (sensor, antenna, Bluetooth chip, amplifier, accelerometer, resistor, capacitor, inductor, etc.) that's attached to the elastomer. The islands are connected by stretchy "bridges" made of thin, spring-shaped copper wires, allowing the circuits to stretch, bend and twist without compromising electronic function.

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