Stomach acid powers sensors

February 07, 2017 //By Nick Flaherty
Researchers at the Massachusetts Institute of Technology and Brigham and Women's Hospital in the US have developed a small voltaic cell that is powered by acid in the stomach.

The system, developed with backing from chip maker Texas Instruments, generates enough power to run a temperature sensor and wireless link for several days. This could offer a safer and lower-cost alternative to the traditional batteries, as these can cause burns when swallowed.

"We need to come up with ways to power these ingestible systems for a long time," says Giovanni Traverso, a research affiliate at the Koch Institute for Integrative Cancer Research and a gastroenterologist and biomedical engineer at Brigham and Women's Hospital. "We see the gastro-intestinal (GI) tract as providing a really unique opportunity to house new systems for drug delivery and sensing, and fundamental to these systems is how they are powered."

The researchers attached zinc and copper electrodes to the surface of their ingestible sensor. The zinc emits ions into the acid in the stomach to power the voltaic circuit, generating enough energy to power a commercial temperature sensor and a 912MHz transmitter.

In tests in pigs, the devices took an average of six days to travel through the digestive tract. While in the stomach, the voltaic cell produced enough energy to power a temperature sensor and to wirelessly transmit the data to a base station located 2 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% of the power it produced in the stomach. "But there's still power there, which you could harvest over a longer period of time and use to transmit less frequent packets of information," said Traverso.

The current prototype of the device is a cylinder about 40 millimeters long and 12 millimeters in diameter, but the researchers anticipate that they could make the capsule about one-third that size by building a customized ASIC with the energy harvester, transmitter, and a small microprocessor.