The electronic skin can be reconfigured,  which means it can be worn on any part of the human body. (Image Credit: Chuanqian Shi)

Researchers at the University of Colorado Boulder have developed a thin, skin-like wearable electronic device that is fully recyclable and has the ability to self-repair. The stretchable circuit board can easily stick to human skin and be reconfigured to fit any area on the human body. It's also capable of performing sensory tasks such as tracking daily step count and measuring the body temperature and heart rate. Additionally, the electronic skin could be an alternative to wearable devices in the future.


"If you want to wear this like a watch, you can put it around your wrist," said Jianliang 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."


The team says this new recyclable high-tech skin could allow wearers to collect accurate data about their bodies while reducing electronic waste around the world. By 2021, humans could potentially produce up to 55 million tonnes of discarded smartphones, laptops, and other electronics.  "Our solution to electronic waste is to start with how we make the device, not from the endpoint, or when it's already been thrown away," Xiao said. "We want a device that is easy to recycle."


To manufacture the electronic skin, the researchers used a screen printing technique to produce a network of liquid metal wires. Then, they covered the circuits between two thin films comprised of polyimine, a highly flexible and self-healing material. The final product is a bit thicker than a Band-Aid and can be applied to the skin using heat. It can also be stretched in any direction by 60% without obstructing any of the internal electronics.


This device can be stretched in any direction by 60% without damaging the electronics. (Image Credit: Chuanqian Shi)


"Smartwatches are functionally nice, but they're always a big chunk of metal on a band," said Wei 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."


What's more impressive is that the device self-heals if it gets damaged. All the wearer needs to do is pinch the damaged areas together. In a few minutes, the bonds that hold the polyimine material together start reforming.  Then, the affected area completely heals itself in as little as 13 minutes.

"Those bonds help to form a network across the cut. They then begin to grow together," Zhang said. "It's similar to skin healing, but we're talking about covalent chemical bonds here."


The researchers designed this device so that it doesn't end up in landfills. If one of these patches is dunked into a recycling solution, the polyimine depolymerizes or separates into its component molecules. All of this happens while the electronic components descend to the bottom. The electronics and flexible material can be used again. 


This newly-developed electronic skin is a long way from competing with wearable devices. It still needs to be connected to an external source of power to operate. However, the team hinted that cyborg skin could be the fashion fad of the future.


"We haven't realized all of these complex functions yet," Xiao said. "But, we are marching toward that device function."


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