A team of engineers at the University of Michigan, Ann Arbor, found that networks of spherical nanoparticles embedded in elastic materials could make the best stretchy conductors. Flexible electronics have a wide variety of possibilities, they say, from bendable displays and batteries to medical implants that move with the body.

Finding good conductors that can still work well even when pulled to twice their length is a tall order and the team found that spherical gold nanoparticles embedded in polyurethane far and away the best in terms of stretchability and concentration of electrons. They used state-of-the-art electron microscope images of the materials at various tensions and found that the nanoparticles started out dispersed but aligned into chain form when stretching. A blood-vessel-like web of nanoparticles emerged in the material upon stretching and disappeared when the material relaxed.

"Essentially the new nanoparticle materials behave as elastic metals," said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering. "It's just the start of a new family of materials that can be made from a large variety of nanoparticles for a wide range of applications."

The engineers chiefly see their stretchable conductors as electrodes, particularly for brain implants. Rigid electrodes create scar tissue that prevents the electrode from working over time, but electrodes that move like brain tissue could avoid damaging cells. “They can alleviate a lot of diseases—for instance, severe depression, Alzheimer's disease, and Parkinson's disease,” Kotov said. “They can also serve as a part of artificial limbs and other prosthetic devices controlled by the brain.”

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