Gastric environment helps power ingestible devices

Last Updated: 2017-02-14

By David Douglas

NEW YORK (Reuters Health) - Electrochemical dissolution of electrodes by ambient acid has powered a temperature transmitter over the six-day course of transit through a pig's gastrointestinal tract.

As Dr. Giovanni Traverso told Reuters Health by email, "We demonstrated the capacity to harvest energy for nearly a week from the stomach of a large mammal that fed and ambulated normally."

In a February 6 online paper in Nature Biomedical Engineering, Dr. Traverso of Brigham and Women's Hospital, Boston, and colleagues note that with advancing technology, power demands of complementary metal-oxide-semiconductors have been reduced to nanowatt (nW) levels. With such efficacy comes the prospect of bio-compatible galvanic cells and electronics that disappear at the end of their task.

Currently, the team points out that wireless power transfer via near-field or mid-field coupling is challenging. And "there is still a strong reliance on primary cell batteries for ingestible electronics." However, primary cells "often require toxic materials, have limited shelf life due to self-discharge, and can result in mucosal injury."

Thus, continued Dr. Traverso, "The ability to harvest energy over prolonged periods of time could help establish gastric resident diagnostic systems as well as gastric resident drug delivery technologies which could be applied on the order of weeks."

As part of that effort, the team developed an energy harvesting system using zinc and copper electrodes. This was attached to a commercial temperature sensing and 920 mHz wireless communication device and deployed in a porcine model.

Detailed characterization experiments using a controllable load resistance showed that there was an average available power density of 1.14 microwatts per mm2 of electrode area for a mean duration of five days in the gastric cavity. This was limited by the time the device was in the stomach. They also demonstrated a power density of 13.2 nW per mm2 of electrode area in the small and large intestine.

The devices took an average of six days to travel through the pigs’ digestive tract. While in the stomach, the cell produced enough energy to power the temperature sensor and to wirelessly transmit the data to a base station located two meters away, with a signal sent every 12 seconds.

Once the device moved into the small intestine, which is less acidic than the stomach, the cell generated only about 1/100 of what it produced in the stomach. However, Dr. Traverso added in a statement, "There's still power there, which you could harvest over a longer period of time and use to transmit less frequent packets of information."

And, say the investigators, "Research in ultra-low-power electronics continues to push the boundaries of the average power consumption, and already provides a range of options for circuits that could be adapted for use in GI applications at the nanowatt level."

In particular, they point out, "The device we have fabricated could be rapidly implemented for the evaluation of core body temperature and for the evaluation of GI transit time given the differential temperature between the body and the external environment."

In fact, they note, a recent study evaluating data from more than 8,000 patients found that peripheral temperature readings did not have acceptable accuracy to guide clinical decisions. "Hence," they conclude, "continuous automated central temperature measurements via a wireless ingestible system may provide significant clinical benefit."

SOURCE: http://go.nature.com/2khQA20

Nature Biomed Eng 2017.