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Surgical Agents Developed for Biopsies in Confined Spaces

Illustration depicting a mu-gripper  near the opening of an endoscopic catheter

Illustration depicting a mu-gripper near the opening of an endoscopic catheter (Evin Gultepe, Gracias Lab, Johns Hopkins University)

Researchers at Johns Hopkins University in Baltimore created and tested microscopic devices powered by body heat that collect tissue samples from patients for biopsies. A team led by Johns Hopkins physician Florin Selaru and engineer David Gracias published its findings in the April issue of the journal Gastroenterology, as well as the 25 January issue of the journal Advanced Materials (paid subscription required).

The devices, called mu-grippers — mu is the Greek letter representing the term “micro” — make it possible to collect tissue samples for biopsies in very confined spaces in the body, which would otherwise require surgery. Mu-grippers can also collect more complete samples, which can reduce the chance of missing diseased lesions in the colon or other organs. For diseases such as cancer, biopsies offer the best evidence to make a deicision on the nature of suspect tissue.

“Based on a small sample, you can’t always draw accurate inferences,” says Selaru. “We need to be able to do a larger statistical sampling of the tissue.” Because of their small size, about the size of a dust particle, mu-grippers can be sent in large numbers to collect evidence. “We could deploy hundreds or even thousands of these grippers to get more samples and a better idea of what kind of or whether a disease is present,” adds Selaru.

Mu-grippers are made of nickel through a photolithographic process similar to fabricating semiconductors. They are printed in a star-like pattern with extensions resembling fingers stretching out from the middle of the device that normally curl inward. However, the device is covered with polymer resin and refrigerated, which keep it rigid until sent into the body. The device operates independently, without wires or tethers.

For a biopsy, a catheter inserts hundreds of mu-grippers into the designated region. Within about five minutes, the natural body heat warms the device, causing the polymer coating to soften. The fingers curl inward in their normal motion to grasp and hold a sample of tissue, after which an inserted magnetized retrieval tool attracts the nickel in the devices for collection.

The April 2013 paper reports on tests to collect samples from the colon and esophagus of pigs, whose organs are similar to humans. In the January paper, the team tested the technology in the bile duct of a pig.

“This is the first time that anyone has used a sub-millimeter-sized device, the size of a dust particle, to conduct a biopsy in a live animal, says Gracias. “And because we can send the grippers in through natural orifices, it is an important advance in minimally invasive treatment and a step toward the ultimate goal of making surgical procedures noninvasive.”

Despite the success with lab animals, the technology still needs extensive testing with human subjects, particularly for safety. Nonetheless, Johns Hopkins University filed provisional patents on the technology and is seeking both grant money and investors to continue research and development. “It is more a question of money than time as to how long it will take before we could use this in human patients,” notes Selaru.

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