You Want to Put a Swarm of Magnetic Micro-Claws Where?

A "mu-gripper" next to a catheter
A “mu-gripper” next to a catheter

Photo by Evin Gultepe, Gracias Lab, Johns Hopkins University.

Earlier this week we talked about a frog-inspired robot that may one day be set loose inside your gut to assist with surgery. Now the tech du jour is an army of dust-sized claws capable of performing biopsies by swarm.

Biopsies remain an enormously useful tool in medicine, especially for the detection of cancers and the diagnosis of inflammatory diseases. But it can be an imperfect science.

Normally, a patient suspected of having ulcerative colitis—a disease of the colon the researchers use for an example in their paper in this month’s Gastroenterology—has to endure at least 33 traditional biopsies over a randomized pattern. That may sound like a lot (we are talking about the colon here), but this samples less than 0.3 percent of the colon’s mucous membrane and may miss precancerous cells or small lesions that could be treated if detected early on. The researchers determined these methods would detect a hypothetical mucosal lesion just 8 percent of the time. (Hypothetical mucosal lesions are the best kind to have, by the way.)

But what if you were to pepper the colon with a cloud of 300 chompie-chomps? Researchers at Johns Hopkins have developed a ninja star-shaped surgical tool they call μ-grippers (pronounced “mu-grippers” as mu is the Greek letter that represents “micro”). The microgrippers are capable of being inserted en masse with a catheter, allowing researchers to draw samples from difficult-to-reach areas like bile ducts. The micrograbbers found the lesion 45 percent of the time. And when you boost the swarm up to 1,500, the efficiency leaps to a whopping 95 percent.

What’s really cool about the little surveyors is that they require no wires, tethers, or batteries. The arms of each millimeter-long star are composed of chromium and gold hinges that naturally want to bend inwards like a closed fist. A thin layer of polymer coating keeps the arms open until it warms up to 98.6 degrees Fahrenheit, whereupon the coating dissolves and the talons snatch up whatever cells they’re closest to. Then, because the base is nickel, the biopsy claws can be removed using a magnet on the end of an endoscopy tool.

This isn’t just hypothetical, by the way. The team of engineers and physicians inserted microgrippers into pigs, both living and dead. (The paper even gives a shout-out to Wagner’s Meats LLC for all the fresh pig colons!) In all cases, the heat-activated claws have shown themselves capable of recovering high-quality tissue samples that stood up to typical genetic and cell testing.

In another paper published this January in Advanced Materials, the Johns Hopkins researchers describe how the polymer coating could be tweaked to release at different intervals, thereby allowing the claws to reach new targets. Furthermore, using polymers that react to different triggers, like enzymes or other biochemicals, might one day give the mini-mousetraps the ability to save their bite until they reach diseased sites. Utilizing biodegradable materials may also help address the concerns of what happens when some of the claws get left behind.

Yeah, I probably should have mentioned that sooner. When you release a couple hundred specks of metal into a living body, some of those soldiers are going AWOL. This is the way of swarms—they perform swimmingly as a group, but individuals don’t always live up to your expectations. So far, the researchers show an average retrieval rate of 95 percent and speculate that the risks of leaving some mu-grippers behind are minimal, given the tools’ size and the body’s ability to process foreign bodies.

Still, who wants a few dozen grabby-claws floating willy-nilly through the digestive track?