From MIT Tech Review:
A gripper based on the current design could respond autonomously to chemical cues in the body. For example, it might react to the biochemicals released by infected tissue by closing around the tissue, so that pieces can be removed for analysis.
Gracias [David Gracias, biomolecular and chemical-engineering professor at JHU] and his colleagues presented the microgripper at the American Chemical Society meeting earlier this month. To demonstrate the device, they used it to grasp and maneuver tiny beads and clumps of cells in a petri dish. They have also used the device in the laboratory to perform an in vitro biopsy on a cow's bladder. "This is the first micromachine that has been shown convincingly to do very useful things," Gracias says. "And it does not require electric power for operation."
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.
ReWalk™, the first commercially viable upright walking assistance tool, enables wheelchair users with lower-limb disabilities to stand, walk, and even climb stairs. For potentially millions of wheelchair users.