Belly battery

CAMBRIDGE, Mass.--While ingestible sensors have existed for a while, the question of how to safely power them remains. Such devices are generally powered by tiny batteries, but they self-discharge over time and are a potential safety risk. A team of scientists from MIT and Brigham and Women's Hospital might have an answer to that issue, however, with a recent announcement of the development of a small voltaic cell powered by the acidic fluids produced in the stomach. In addition to being a safer alternative, it's expected these cells will also be lower in cost.

“This work could lead to a new generation of electronic ingestible pills that could someday enable novel ways of monitoring patient health and/or treating disease,” said senior author Robert Langer, the David H. Koch Institute Professor at MIT.

Langer and Giovanni Traverso, a research affiliate at the Koch Institute for Integrative Cancer Research, were both senior authors on this work, and have previously developed other ingestible devices that can track temperature, respiration and heart rate, or deliver drugs internally. Anantha Chandrakasan, head of MIT’s Department of Electrical Engineering and Computer Science and the Vannevar Bush Professor of Electrical Engineering and Computer Science, was a third senior author, while MIT postdoc Phillip Nadeau was the lead author.

The latter two brought with them experience in developing low-power electronics.

Their strategy for the voltaic cell consisted of attaching zinc and copper electrodes to the surface of the sensor. The zinc gives off ions into the stomach acid to power the circuit, and this produces enough power to run a commercial temperature sensor and a 900-megahertz transmitter, allowing the data to be wirelessly transmitted to a station 2 meters away with a signal sent every 12 seconds.

The device has been tested in pigs, where it was found to take an average of six days to make its way through the digestive tract.

These devices produce significantly less power in the small intestine—as it's less acidic, the cell only produces roughly 1/100 of the power generated in the stomach—but Traverso said it could still be used to transmit less-frequent information bursts. At present, the cylindrical device is roughly 40 millimeters long and 12 millimeters in diameter, but the team believes they can reduce it to about one-third that size if they build a customized integrated circuit to carry the energy harvester, transmitter and a small microprocessor. In addition, once it's miniaturized, they expect to be able to add other sensors and developments to enable options such as long-term monitoring of vital signs.

“You could have a self-powered pill that would monitor your vital signs from inside for a couple of weeks, and you don’t even have to think about it. It just sits there making measurements and transmitting them to your phone,” Nadeau explained.

These devices also have applications as drug delivery vehicles, as the researchers were able to use the power from the voltaic cell to release drugs stored in a gold film.

“A big challenge in implantable medical devices involves managing energy generation, conversion, storage and utilization. This work allows us to envision new medical devices where the body itself contributes to energy generation enabling a fully self-sustaining system,” added Chandrakasan.

This work was funded by Texas Instruments, the Semiconductor Research Corporation’s Center of Excellence for Energy Efficient Electronics, the Hong Kong Innovation and Technology Commission, the National Institutes of Health and the Max Planck Research Award.

SOURCE: MIT press release