A small handlike gripper, only about 500-µm diameter when open, can grasp tissue or cell samples making it easier for doctors to perform minimally invasive surgery, such as biopsies. The tiny device can be magnetically guided around from outside the patient. Its “fingers” curl around an object when chemically triggered. The design responds autonomously to chemical cues in the body. For example, it might react to the biochemicals released by infected tissue to remove pieces for analysis. The idea is to let surgical tools move more freely inside a body. “We want to make mobile surgical tools,” says Johns Hopkins University Biomolecular and Chemical-Engineering Professor David Garicas, who led gripper development.

The gripper is made of a film of copper and chromium covered with polymer. As long as the polymer stays rigid, the gripper remains open. But introduce a chemical trigger or lower the temperature and the polymer softens, actuating the gripper's fingers so they curl inward to form a ball about 190-µm wide. Another chemical signal can open the gripper. All chemicals used as triggers in experiments are harmless to the body.

Minimally invasive surgery has involved making centimeter-size incisions and inserting surgical tools. In conventional microsurgery, wires connect tools to external controls, but physical controls limit a surgeon's ability to maneuver instruments.

Gracias and his colleagues have demonstrated the device grasping and maneuvering 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. Because the gripper needs no connection to controls outside the body, it could mean more dexterous microsurgery, adds UCLA Mechanical Engineering Professor Chang-Jin Kim. Microgrippers could also be useful in chip-sized labs, for example, moving samples around or cleaning away debris. But Kim points out that using chemical triggers from in the environment makes the device tricky to control. “When the environment changes, performance changes,” he adds.

Gracias hopes to shrink the gripper to about 10-µm wide and let it move in response to different chemical concentrations, such as bacteria moving toward higher concentrations of sugars. To see the gripper in action, go to http://tinyurl.com/5cabrt