The open gripper is 500 micrometers (0.05 centimeters) in diameter, and it is made of a film of copper and chromium covered with polymer. As long as the polymer stays rigid, the gripper remains open. But introducing a chemical trigger or lowering the temperature causes the polymer to soften, actuating the gripper’s fingers so that they curl inward to form a ball that is 190 micrometers wide. Another chemical signal can be used to reopen the gripper. All of the chemicals used as triggers in experiments are harmless to the body.
Since the new technology does not need to be connected to controls outside the body, it could mean more dexterous microsurgery, says Chang-Jin Kim, a mechanical-engineering professor at the University of California, Los Angeles. “You don’t have to have a physical connection, and that is pretty attractive,” he says.
Microgrippers could also be important for lab-on-a-chip applications–for example, moving samples around a chip or cleaning away debris. But Kim says that using chemical triggers from the environment makes the Johns Hopkins device tricky to control. “If the environment changes, your performance changes,” he adds.
Kim and his colleagues previously developed a four-fingered “microhand” that opens and closes when gas pressure is changed inside tiny polymer balloons at the finger joints. The microhand offers more precise control but must be tethered to a control unit. Nonetheless, Kim says that his device could have a wider range of uses–as a tool for remotely removing detonators from explosives, for example.
The new technology, meanwhile, is designed exclusively for surgery. Gracias hopes to shrink the gripper further–to about 10 micrometers wide–and to enable it to move in response to different chemical concentrations, like a bacteria moving toward higher concentrations of sugars.