Gold Is The Secret Ingredient For Stretchy Conductors

by Masha Vodyanik, age 16

Scientists at the University of Michigan recently engineered an important conductor made of gold nanoparticles and an elastic polymer. But what looks like a shiny piece of gold foil and stretches like a rubber band could potentially be made into electrode implants for the brain or the heart.

When used as implants in the brain, conductive material like this one have the potential to treat conditions like movement disorders. In the heart, they could regulate cardiac activity. The material could be designed to bend, mold and stretch according to the human body, sticking over skin like temporary tattoos or rewiring circuits inside the body itself.

Unlike in other circuits, this stretchy plastic material retains its electric conductivity when stretched to four times its original length. Other stretchable circuits use accordion or spring-like folding wires that expand or contract so stretching will not disturb the flow of electrons through the circuit. With the new gold material, however, folds aren’t necessary because it retains all of its metallic properties when stretched. When fully stretched, conductivity is decreased by over 90 percent but it is still enough to provide conductivity to some devices.

The secret is self-organizing gold nanoparticles that are embedded into an elastic polymer. When the material is stretched, these tiny gold spheres organize themselves into conductive chains that fill gaps in the elongated material. Under pressure, electrons flow through these gold nanosphere ropes and the circuit runs uninterrupted. When stress is relieved, nanospheres go back to their original positions.

Currently, there are on-going tests with prototype implants on rat brains. Teams are also testing whether other nanoparticles besides gold can be used to create stretchy conductors.

“The results suggest some very interesting, unexpected effects of nanoparticle-elastomer composites,” said John Rodgers, a scientist at the University of Illinois. Scientists’ current goal is to move from a stretchy conductor to a functioning electronic system that serves a purpose in the heart or the brain.