Is this metal-coated paper the start of the future for wearable devices?
- The metal-coated paper can be folded but has properties of metal, such as tunable stiffness and ability to conduct heat and electricity
- ‘We can also create electric circuits on the skin to monitor finger movements, the heart’s activity and body temperature’
The metal-coated paper can be folded as usual, but is enhanced by the added properties of metal, such as tunable stiffness as well as the ability to conduct heat and electricity. It allows a 3D paper structure to be controlled by electricity, temperature changes or magnets.
“This facile approach provides a new material option for the wearable testing platform and flexible devices as well as soft robotics,” the team from Tsinghua University, Beihang University and the Chinese Academy of Sciences wrote in an article published in the peer-reviewed journal Cell Reports Physical Science on Friday.
A common example of liquid metal is mercury, a toxic silvery-white metal that is liquid at room temperature. It freezes into a soft solid around -39C (-38F).
In this study, the team made use of two non-toxic liquid metal alloys eGaIn, which melts at 15.5C, and BiInS, with a melting point of 62C.
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Scientists have found sticking liquid metal to surfaces such as paper, plastic, cloth and even human skin difficult because of its extremely high surface tension and some have experimented with using an adhesive. But adding a third material may weaken the product’s electrical, thermal or mechanical performance, the researchers say.
The Chinese team made it possible by first applying liquid metal to silicone stamps, then rubbing the stamps with force on to paper so the metal droplets could effectively bind to the paper.
The scientists showed that the metal-coated paper could still be folded into different shapes – such as a crane and a collapsible box – as with uncoated paper.
They also folded the treated paper into a springlike shape. Thanks to the self-glueing ability of liquid-metal enhancers, the spring remained at its most compressed status and could be stretched to the required length or height when needed.
The metal can be solidified by cooling and returns to its original state after reheating. The scientists had it carry a 50-gram (1.8 oz) weight in the study, showing its potential as a multifunctional smart material.
Lead author Yuan Bo, a postdoctoral fellow in the department of biomedical engineering at Tsinghua University in Beijing, said liquid metal coating could turn commonly available materials into durable smart electronic devices.
“Devices like robotic grippers are conventionally powered by compressed air or heat and built with customised materials,” Yuan said. “Now we can use paper to make them.
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“When we power the metal paper gripper with electricity, it expands. Without electricity, it tightens to pick up an item. After the item is moved to its destination, the gripper is powered again to release the object.
“We can also create electric circuits on the skin to monitor finger movements, the heart’s activity and body temperature,” she said.
She said the coating was affordable, required only a thin layer of metal and could be recycled by solidifying and peeling it from the surface it coated.
Yuan added that the team would work on protecting the liquid metal coating from melting by touch, as well as expanding its applications to more surfaces, such as other metals and ceramics.
