MIT scientists have developed a small battery that runs on stomach acids and could power next-generation ingestible electronic pills which may monitor patient health or treat diseases by residing in the gastrointestinal tract for extended periods of time.

The device may offer a safer and lower-cost alternative to the traditional batteries now used to power such devices, researchers said.

"We need to come up with ways to power these ingestible systems for a long time," said Giovanni Traverso, from Massachusetts Institute of Technology's (MIT) in the US.

"We see the gastrointestinal 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," Traverso said.

Researchers have previously built and tested many ingestible devices that can be used to sense physiological conditions such as temperature, heart rate, and breathing rate, or to deliver drugs to treat diseases such as malaria.

"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 Robert Langer, professor at MIT.

Such devices are usually powered by small batteries, but conventional batteries self-discharge over time and pose a possible safety risk.

Researchers took inspiration from a very simple type of voltaic cell known as a lemon battery, which consists of two electrodes – often a galvanised nail and a copper penny – stuck in a lemon.

The citric acid in the lemon carries a small electric current between the two electrodes.

To replicate that strategy, 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 900-megahertz 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 two metres 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 a hundredth of what 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," Traverso said.

The current prototype of the device is a cylinder about 40 millimetres long and 12 millimetres in diameter, but the researchers anticipate that they could make the capsule about one-third that size.

The study was published in the journal Nature Biomedical Engineering.