Stretchy Electronics Made from Stiff 'Islands'

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A checkerboard of rigid electronic components have been embedded into a flexible surface that can be stretched three times its normal length. The technique makes it possible to keep stiff circuit boards safe from kinks, while at the same making wearable flexible computers more feasible.

"We want to put this on something like

rubber," André Studart told Discovery News. Studart is a professor

of complex materials at Swiss Federal Institute of

Technology (ETH) and one of the co-authors of the paper in Nature Communications outlining

the work.

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Rather than try to make the electronics stretch, Studart and his colleagues decided to make a surface for the electronics to sit on that had both stretchy and stiff regions. The stretchy areas give the flexibility while the stiff regions protect the rigid electronic circuits. 

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The surface is comprised of polyurethane, the same substance used in skateboard wheels and floor

coatings. Polyurethane can me made stiffer or softer depending on what

it's mixed, or doped, with. The researchers used laponite, which is a

kind of clay, and micrometer-sized bits of aluminum. The polyurethane doped with aluminum is stiffer than that with laponite, which in

turn is stiffer than polyurethane not mixed with anything.

To make their polyurethane both stretchy and stiff, the team made a sheet of it that consisted of several layers. The bottom layer is the most flexible, and made of undoped polyurethane. The middle layer is made of polyurethane doped with laponite. The very top layer is the the most rigid, the one doped with aluminum. While the stretchiest layer on the bottom is a large sheet, the stiffer ones are laid down in cut-out squares and bonded to the undoped polyurethane layer.

The team tested the surface by installing an LED circuit on the stiff island. The LED stayed lit even

when the sheet was stretched to 150 percent of its length.

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This isn't the only way to do

flexible electronics. John Rogers, at the University of Illinois, has been

working on several methods to stretch electronics, dissolve them and even stick them to skin. He said the

work here is "a

nice, new addition to the toolbox."

Rogers said his lab has been

focused at the level of designing systems, which sometimes involves coming up with new

ways to build semiconductors. In one case he used a serpentine pattern of

metal wires, which could stretch like a spring on the surface of a

balloon. "The latest work from Switzerland

could have value in the context of an application of this sort, as an

alternative to the interconnection wiring that we used."

Credit: Rafael Libanori, Randall M. Erb and André R. Studart

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