In a step toward robots smaller than a grain of sand, University of Michigan researchers have shown how chains of self-assembling particles could serve as electrically activated muscles in the tiny machines.
"We are inspired by ideas of microscopic robots," said Michael Solomon, a professor of chemical engineering. "They could work together and go places that have never been possible before."
Solomon and his group demonstrated that some gold plating and an alternating electric field can help oblong particles form chains that extend by roughly 36 percent when the electric field is on.
The team started with particles similar to those found in paint, with diameters of about a hundredth the width of a strand of hair. They stretched these particles into football shapes and coated one side of each football with gold. The gilded halves attracted one another in slightly salty water—ideally about half the salt concentration in the sports drink Powerade. The more salt in the water, the stronger the attraction.
Left to their own devices, the particles formed short chains of overlapping pairs, averaging around 50 or 60 particles to a chain. When exposed to an alternating electric field, the chains seemed to add new particles indefinitely. But the real excitement was in the way that the chains stretched.
"We want them to work like little muscles," said Sharon Glotzer, the Stuart W. Churchill Professor of Chemical Engineering. "You could imagine many of these fibers lining up with the field and producing locomotion by expanding and contracting."
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