Ingestible origami robot unfolds inside the stomach to remove button batteries

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The accordion-style origami robot folds up to fit inside an ice capsule that is small enough to swallow(Credit: Melanie Gonick/MIT)

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It's one thing to have butterflies when you're nervous, but envision a tiny robot crawling around inside your stomach. Researchers have developed an ingestible origami robot to do just that. Swallowed as a capsule, the robot then unfolds in true Transformers style to patch a wound or remove foreign objects, such as button batteries.

This isn't the first origami-inspired robot we've seen and builds on previous work in the field. The result of a collaborative effort with scientists from MIT, the University of Sheffield and the Tokyo Institute of Technology, the bot consists of a heat-sensitive material sandwiched between two layers of structural material.

When heated, the sandwiched layer contracts causing the robot to fold according to a slit pattern on its outer layers. For this particular bot, the team used a type of dried pig intestine commonly used in sausage casings, as the structural material, while the contracting layer is made of a biodegradable shrink wrap called Biolefin.

To create a robot that a person could ingest, the team had to come up with a design compressible enough to fit in a capsule. The researchers then encased this in an ice capsule, which melts away when it reaches the stomach allowing the robot to unfold. Through a lot of trial and error, the researchers arrived at an accordion style robot design that could unfold into a rectangle.

To get the robot to move inside a stomach, the team applied magnetic fields to control the motion of a permanent magnet embedded in one of the robot's accordion folds. By changing the magnetic fields, they were able to make the robot rotate with enough precision to remove a button battery stuck to the wall of a synthetic stomach.

"For applications inside the body, we need a small, controllable, untethered robot system," says the Director of MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL), Daniela Rus. "It's really difficult to control and place a robot inside the body if the robot is attached to a tether."

The bot can move around using a "stick-slip" motion. Friction causes its appendages to stick to a surface when it executes a move and when it flexes, it causes a change in its weight distribution allowing it to slip free. The biocompatible material used, however, turned out to be quite malleable so the team had to come up with some design modifications to allow the bot to move inside a fluid-filled stomach .

"In our calculation, 20 percent of forward motion is by propelling water — thrust — and 80 percent is by stick-slip motion," says Shuhei Miyashita, first author on the paper. "In this regard, we actively introduced and applied the concept and characteristics of the fin to the body design."

While there are many potential applications, the group hopes that their origami robot can be used to remove swallowed button batteries stuck to the wall of a stomach, of which around 3,500 are reported in the U.S. every year. These don't cause an issue if they are digested normally, but if the battery ends up in prolonged contact with the tissue of the stomach or esophagus, it can burn the tissue and wound the area.

"If you have a battery in your body, you really want it out as soon as possible," says Rus. "It's really exciting to see our small origami robots doing something with potential important applications to health care."

The ingestible robot is shown in the video below.

Source: MIT

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