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Swarms of tiny "microgrippers" used to perform biopsies

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April 29, 2013

A 300-micrometer microgripper at the opening of a cathether

A 300-micrometer microgripper at the opening of a cathether

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When procuring tissue samples for medical diagnosis, doctors have been confined to bulky and invasive forceps. But with recent successful experiments in pigs, we may see doctors switching from the single forceps to hordes of a thousand "microgrippers." These metal discs, each only 300 micrometers in size, are designed to snip bits of tissue when introduced en masse into the body and then be easily retrieved by a doctor. Their small size, added to the fact that they need no batteries, tethers or wires, belies their complexity and autonomy in function, which could allow the microgrippers to provide diagnoses earlier, more easily, and with less trauma.

Resembling sprinklings of dust to the naked eye, or star-shaped confetti under a microscope, microgrippers are produced in similar fashion to computer chips. They're made of nickel, making them magnetically retrievable, and their ability to grip comes from a heat-sensitive polymer layer on the tips and joints of their arms. At 32° F (0° C) the star shape is flat and rigid. However, at 98.6°F (37° C), or body temperature, the polymer softens, forcing the star to close tightly in on itself and grip whatever it was in contact with.

The question of whether microgrippers become useful boils down to a numbers game. Tissue samples, even when combined with other medical observations, are the most important factor for establishing an accurate diagnosis, yet by definition are taken randomly. The use of forceps is limited to a certain number of random biopsies in a given organ because of the tool's size and the amount of trauma caused with each excision. Using microgrippers allows one to increase the sampling by a magnitude of ten or even a hundred.

Dr. Gracias at Johns Hopkins designed the microgrippers, and his team has conducted two tests, one of them using a pig's colon as a model because of its similarity to a human's. Before being introduced to a colon via an endoscope, the grippers are kept rigid in cold water. After five minutes in the body, the polymer hinges are warm enough to clasp closed over a piece of tissue. It is then straightforward to retrieve thousands of grippers using a magnetic catheter.

However, if you've ever spilled a tin of tacks or pins on a soft carpet and attempted to collect them all, even with a magnet you know that retrieval will still be difficult. Some microgrippers are certain to be left behind. Though colon tissue quickly regenerates itself, shedding grippers that may have been left behind, the next direction of research is establishing safety.

With future advances in sophisticated "microtechnologies" (the microgrippers are just a little too big to describe as nanotechnology), doctors may one day use thousands of tiny tools where one would serve today.

Sources: Gastroenterology, Johns Hopkins University

About the Author
Heidi Hoopes Heidi measures her life with the motley things she's done in the name of scientific exploration. While formally educated in biology and chemistry, informally she learns from adventures and hobbies with her family. Her simple pleasures in life are finding turtles while jogging and obsessively winnowing through her genetic data.   All articles by Heidi Hoopes
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