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JUL/AUG 2013  

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Microrockets and micromotors may help overcome medical barriers

An advance in micromotor technology akin to the invention of cars that fuel themselves from the pavement or air, rather than gasoline or batteries, is opening the door to broad new medical and industrial uses for these tiny devices, according to scientists from the University of California, who presented their research at a meeting of the American Chemical Society in April.


The motors are so small that thousands would fit inside this “o”.

Joseph Wang, who leads the research on the motors, said that efforts to build minute, self-powered robot devices have evoked memories of the 1966 science fiction film "Fantastic Voyage." It featured a miniaturized submarine, which doctors injected into a patient. It then navigated through blood vessels to remove a blood clot in the brain.

Fuel and propulsion systems have been a major barrier in moving science fiction closer to practical reality, Wang explained. Some micromotors and even smaller nanomotors have relied on hydrogen peroxide fuel, which could damage body cells. Others have needed complex magnetic or electronic gear to guide their movement.

wang 

Self-propelled microrockets (left, purple) and micromotors (right, green) could someday deliver drugs, perform microsurgery or clean up oil spills. Credit: Wei Gao and Joseph Wang, Ph.D.

“We have developed the first self-propelled micromotors and microrockets that use the surrounding natural environment as a source of fuel,” Wang said. “The stomach, for instance, has a strongly acid environment that helps digest food. Some of our microrockets use that acid as fuel, producing bubbles of hydrogen gas for thrust and propulsion. The use of biocompatible fuels is attractive for avoiding damage to healthy tissue in the body. We envision that these machines could someday perform microsurgery, clean clogged arteries or transport drugs to the right place in the body. But there are also possible uses in cleaning up oil spills, monitoring industrial processes and in national security.”

Wei Gao, a graduate student in Wang’s lab, described how the team at the university has developed two types of self-propelled vehicles: microrockets made of zinc and micromotors made of aluminum. The tubular zinc micromotor is one of the world’s fastest, able to move 100 times its 0.0004-in. length in just one second, according to Gao. That’s like a sprinter running 400 miles per hour. The zinc lining is biocompatible. It reacts with the hydrochloric acid in the stomach, which consists of hydrogen and chloride ions. It releases the hydrogen gas as a stream of tiny bubbles, which propel the motor forward. “This rocket would be ideal to deliver drugs or to capture diseased cells in the stomach,” he said.

The scientists are working on extending the lifetimes of the vehicles so that they last longer, and they are functionalizing them for specific biomedical applications. They also are exploring commercial partners for realizing real-life applications of this work, according to Wang.

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