Thursday, July 31, 2008

Controlling a Gut Bot's Position

A swallowable robot can be stuck and unstuck to a spot on command.

By Kristina Grifantini

Robot-capsule anchoring: An initial prototype of the robot-capsule anchors inside a transparent tube, mimicking the way that it would stick in the esophagus. Credit: Metin Sitti, Carnegie Mellon University

Multimedia   Click here to watch a video of the robot capsule anchoring and extending its legs.

For the past few years, medical researchers have been trying to develop ways to peer painlessly inside the human body, from a swallowable sensor to a magnetically controlled image-snapping capsule. Now, a group at Carnegie Mellon University (CMU) has shown that a tiny capsule robot is adhesive enough to anchor inside an intestine and yet gentle enough not to tear soft tissue.

The anchoring robot would be swallowed like a normal pill and move through the body until it reached the gut. Then a doctor, using a wireless control, would tell the robot when to expand its legs and anchor. It would be good not only for snapping images, but also potentially for biopsies, drug delivery, heat treatment, and other treatment applications.

While doctors have, for the past several years, used a camera pill that transmits images of the intestines, being able to control the movement of such a device would have many benefits, says Mark Schattner, a gastroenterologist at the Memorial Sloan-Kettering Cancer Center, who was not involved in the work. "The number-one use would be biopsy," says Schattner. "The other would be control of bleeding--if you could cauterize or laser a source of bleeding, that would be [a] major therapeutic use." While the CMU robot is not yet ready for such uses, its ability to securely and safely anchor in the body is the first step in achieving more-advanced applications.

The trick to making the robot was finding an adhesive that would "stick repeatedly to tissues like intestines, esophagus, stomach, heart, and kidney surfaces," says Metin Sitti, a professor and principal investigator of the NanoRobotics Lab at CMU. Although strong biomedical adhesives exist, they stick once and cannot be removed. Other attempts to create removable adhesives utilized clamps and hooks, which could potentially damage tissue. By developing a strong adhesive that can attach and reattach many times, Sitti hopes to build a robot that can actually crawl inside the human body for therapeutic purposes without causing harm.

Sitti and his lab group looked to beetles, which secrete oil-like liquids along their foot hairs in order to stick securely to surfaces. They coated their robot's feet with a similarly viscous liquid to "help get more adhesion by giving them a surface-tension component," says Sitti. Aside from increasing capillary and intermolecular forces, secretions help feet adhere to rough surfaces by filling in the gaps, he adds.