Mini Dance

Microscopic robots crafted to maneuver separately without any obvious guidance are now assembling into self-organized structures after years of continuing research led by a Duke University computer scientist.

"It is marvelous to be able to do assembly and control at this fine a resolution with such very, very tiny things," says Bruce Donald, a Duke professor of computer science and biochemistry.

Each microrobot is shaped something like a spatula but with dimensions measuring just microns, or millionths of a meter. They are almost 100 times smaller than any previous robotic designs of their kind and weigh even less, Donald adds.

In videos produced by the team, two microrobots can be seen pirouetting to the music of a Strauss waltz on a dance floor just 1mm across. In another sequence, the devices pivot in a precise fashion whenever their boom-like steering arms are drawn down to the surface by an electric charge. New research also describes the group's latest accomplishment: getting five of the devices to group-maneuver in cooperation under the same control system.

The research was funded by the National Institutes of Health and the Department of Homeland Security, and also included Donald's graduate student Igor Paprotny and Dartmouth College physicist Christopher Levey.

Donald has been working on various versions of the MEMS microrobots since 1992, initially at Cornell and then at Stanford and Dartmouth before coming to Duke.

Propelling themselves across such surfaces in an inchworm-like fashion impelled by a "scratch-drive" motion actuator, the microrobots advance in steps only 10 to 20 billionths of a meter each, but repeated as often as 20,000 times a second.

The microrobots can be so small because they are not encumbered by leash-like tethers attached to an external control system. Built with microchip fabrication techniques, they are each designed to respond differently to the same single "global control signal" as voltages charge and discharge on their working parts.

This global control is akin to ways proteins in cells respond to chemical signals, Donald says, who also uses computer algorithms to study processes in biochemistry and biology.

In a new report, the team shows that five of the microrobots can be made to advance, turn and circle together in pre-planned ways when each is built with slightly different dimensions and The robots are initially arranged along the corners of a rectangle with sides 1mm by 0.9mm (top left). During stage one (top right), devices 4 and 5 dock together to form the initial stable shape. In stage two (bottom left), device 3 docks with the initial stable shape, while during stage three (bottom right), device 1 docks with the stable shape, forming the final assembly. (Image courtesy of Duke University) stiffness. Following a choreography mapped out with the aid of mathematics, the microdevices ultimately assemble into group micro-huddles that could set the stage for something more elaborate.

"Initially, we wanted to build something like a car that could drive around at the microscopic scale," Donald says. "Now what we've been able to do is create the first microscopic traffic jam."

Donald and other Duke researchers are now thinking of trying to enlist the maneuverable microrobots to insert tiny, billionths-of-a-meter electrodes called nanotubes into neural cells. The research will be supported by the Duke Institute for Brain Sciences.