The device 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 at the UC San Diego Jacobs School of Engineering.
The new device 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. This work overcomes a technological roadblock to building stretchable electronics in 3D. “The problem isn’t stacking the layers. It’s creating electrical connections between them so they can communicate with each other,” said Xu. These electrical connections, known as vertical interconnect accesses (VIAs), are essentially small conductive holes that go through different layers on a circuit. VIAs are traditionally made using lithography and etching. While these methods work fine on rigid electronic substrates, they don’t work on stretchable elastomers.
A user can stick the ‘smart bandage’ on different parts of the body to wirelessly monitor different electrical signals. When worn on the chest or stomach, it records heart signals like an electrocardiogram (ECG). On the forehead, it records brain signals like a mini EEG sensor, and when placed on the side of the head, it records eyeball movements. When worn on the forearm, it records muscle activity and can also be used to remotely control a robotic arm. The smart bandage also monitors respiration, skin temperature and body motion. “We didn’t have a specific end use for all these functions combined together. The point is that we can integrate all these different sensing capabilities on the same small bandage,” said co-first author Zhenlong Huang, who conducted this work as a visiting Ph.D. student in Xu’s research group.
The researchers did not sacrifice quality for quantity. “This device is like a ‘master of all trades.’ We picked high quality, robust subcomponents and developed a clever way to integrate all these into one stretchable device,” added co-first author Yang Li, a graduate student at UC San Diego in Xu’s research group.
So far, the device can last for more than six months without any drop in performance, stretchability or flexibility. It can communicate wirelessly with a smartphone or laptop up to 10 meters away. The device runs on a total of about 35.6 milliwatts, which is equivalent to the power from 7 laser pointers.