Researchers at the Massachusetts Institute of Technology and Brigham and Women’s Hospital have designed and demonstrated a voltaic cell that is sustained by the acidic fluids in the stomach.

The system can generate enough power to run sensors or drug delivery devices that can reside in the gastrointestinal tract for extended periods of time.

Ingestible voltaic cell sustained by acidic fluids in the stomach.Ingestible voltaic cell sustained by acidic fluids in the stomach.This type of power could offer a safer and lower-cost alternative to the traditional batteries now used to power such devices, the researchers say.

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.

According to the study, 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.

The research team took inspiration from a simple type of voltaic cell known as a lemon battery, which consists of two electrodes—often a galvanized nail and a copper penny. 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 involving 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 1/100th of what it produced in the stomach. But, according to researchers, there’s still power there, which could be harvested over a longer period of time and used to transmit less frequent packets of information.

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

Once the researchers miniaturize the device, they anticipate adding other types of sensors and developing it for applications such as long-term monitoring of vital signs.

Such devices could also be used for drug delivery. In this study, the researchers demonstrated that they could use the power generated by the voltaic cell to release drugs encapsulated by a gold film. This could be useful for situations in which doctors need to try different dosages of a drug, such as medication for controlling blood pressure.

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