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Building a Self-Assembling Stomach-Bot

Modules that self-assemble inside the stomach could perform more-sophisticated diagnosis and treatment.
September 22, 2008

Doctors have long sought better ways to examine the workings of the human body without having to cut their patients open. A swallowable camera, little bigger than a normal pill, can already snap pictures as it floats through the stomach and intestine, offering a less invasive way to perform diagnosis than an endoscope or surgery. Now a consortium of European researchers is testing a way to connect several swallowable devices to create a surgical “robot” that would self-assemble inside the stomach.

Linked up: By using magnetic links between capsules, researchers hope to build a snake-like robot that can self-assemble inside a patient’s stomach.

The Israeli company that developed the first pill cameras, Given Imaging, is currently working on a way to control the movement of its camera capsule from outside the body. Several academic research groups are also looking at ways to let swallowable capsules maneuver themselves by rolling, crawling, or sticking to tissue. With greater control, doctors should be able to better diagnose and possibly even treat illness. But the capabilities of such intestinal devices will still be limited because a capsule must remain small enough to be comfortably swallowed.

A collaboration of researchers from Italy, France, Switzerland, and Spain, called ARES, is testing a way for multiple capsules to automatically snap together. Each would be swallowed individually before assembling into a more complex device once safely in the stomach.

The ultimate goal is for each capsule to perform a different task: one for imaging, one for power, one to take samples, and so on. Once inside the stomach, the capsules would link together, creating a snake-like device that could slide through the intestines, performing more-complex tasks than those performed by a single capsule or several free-floating ones.


  • Click here to see how researchers conducted the self-assembling modular experiment.

  • Click here to see a proof of concept of the swallowable modules in action.

“Instead of having a single capsule, we propose a modular approach where each of the capsules could have different functionalities,” says Zoltán Nagy, a researcher at the Swiss Federal Institute of Technology (ETH), in Zurich, and a member of the ARES project. “Before we can actually talk about such complex robots inside the stomach, we need to solve the fundamental problem of self-assembly. Our work suggests one [way that] this can be done robustly,” says Nagy.

The ETH group decided to use magnets to connect its modules, since they don’t require onboard power and can be easily monitored from outside the body.

To find the best design for the self-assembling capsules, the researchers tested different designs in a plastic model of the stomach filled with liquid. They ran around 50 tests for each of 12 different configurations of module size, magnet type, and magnet arrangement. A single magnet with its positive-negative axis on the surface of a longer capsule worked best, yielding a 75 percent rate of success at linking the two capsules; modifying the magnet module to make it more flexible increased this to 90 percent. The group will present details of the linking modules this week at the International Conference on Intelligent Robots and Systems in France.

“[The] work is interesting as a concept since modular robots assembling inside the body could enable more flexible and complex gastrointestinal-related robotic applications,” says Metin Sitti, a scientist who works on gripping robotic capsules at Carnegie Mellon University. “Current capsules typically get bigger by adding more functionalities … Assembling modules would have [fewer] such issues.”

Stomach test: Researchers at the Swiss Federal Institute of Technology, in Zurich, used a plastic stomach to see which magnetic design links best in a limited space full of liquid.

“One of the main constraints [of the swallowable imaging capsule] is the battery,” says Milan Dodig, a gastroenterologist at Cleveland Clinic, who uses the device to treat his patients. “It takes almost 60 percent of the volume of the capsule; it’s not steerable [and] can still miss stuff. The angle of the images is also limiting, and you can’t see the complete [intestine].”

The ETH team was able to detect how well modules linked together by monitoring changes to the field of each magnet. “With [this] simple method, I can detect if one is connected, which means I can create a picture on the computer,” says Nagy.

The next stage of the research will involve making sure that the magnets do not harm tissue when they lock together. This will involve testing the system in a moving artificial stomach or an animal stomach provided by a partner group. The team also needs to find a way to control how the capsules arrange themselves.

“Something like this that could be swallowed, self-assembled, and remotely controlled would be a major advance,” says Joseph Murray, a gastroenterologist at the Mayo Clinic, who was not involved in the work. However, he says that it will be a challenge to use the magnets safely.

“There is a large demand from physicians to have a steerable, motion-controlled camera,” adds Frank Volke, a project leader at the Fraunhofer Institute for Biomedical Engineering, in Sankt Ingbert, who is helping to develop a technique for steering Given Imaging’s pill camera by magnetically controlling it. “I think it is a very interesting scientific research approach which might take longer for practical use,” Volke says of the ETH work.

Nagy says that the magnetic linking scheme developed by his team could also be used to build search-and-rescue robots that can slither through rubble and into tight spaces. “You can imagine throwing in a couple of pieces of the robot and it self-assembling,” says Nagy.

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