Engineering news
Led by researchers at the University of California in San Diego, the team stacked and connected layers of stretchable circuits into a coin-sized device that is worn on the skin to wirelessly monitor signals from respiration, body motion, temperature, eye movement, and heart and brain activity.
Flexible electronics could be particularly useful for skin-mounted biomedical devices, which have to stay on and keep working as the skin underneath moves and stretches.
“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 senior author Sheng Xu, who was named as one of MIT Technology Review's 35 Innovators Under 35 list in 2018 for his work in the area.
The new device is made of four layers of interconnected stretchable, flexible circuit boards. Each layer is built on a silicone elastomer substrate patterned with an ‘island-bridge’ design of small, rigid electronic parts such as sensors and antennas connected by stretchy ‘bridges’ made of thin, spring-shaped copper wires, allowing the circuits to stretch, bend and twist without compromising electronic function.
A main issue with flexible devices is creating electrical connections between layers. These connections, known as vertical interconnect accesses, are small conductive holes that go through different layers on a circuit. They are traditionally made using lithography and etching, which does not work on stretchable elastomers.
Instead, Xu and his colleagues used lasers to cut holes through the stacked layers of black silicone elastomer. They then filled in the holes with conductive material to connect the layers to each other.
The prototype device contains a variety of sensors and can communicate with a smartphone or laptop up to 10m away.
“This device is like a 'master of all trades',” said co-first author Yang Li. “We picked high-quality, robust sub-components – the best strain sensor we could find on the market, the most sensitive accelerometer, the most reliable ECG sensor, high-quality Bluetooth etc – and developed a clever way to integrate all these into one stretchable device.”
Named the smart bandage by the researchers, the prototype can last for more than six months. They will now work with industrial partners to develop the technology, and they hope to test it in clinical settings.
A paper on the work, which also involved the University of Electronic Science and Technology of China and the US Air Force Research Laboratory, was published in Nature Electronics.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.