New type of power could offer a safer and lower-cost alternative to the traditional batteries used to power sensors and drug delivery devices

A team of researchers at MIT and Brigham and Women’s
Hospital designed and demonstrated a small voltaic cell that’s sustained by the
acidic fluids in the stomach. Impressively, this system can generate enough
power to run small sensors or drug delivery devices that can reside in the
gastrointestinal tract for extended periods of time.

According to the researchers, this type of power can offer a
safer and lower-cost alternative to the traditional batteries used to power
such devices. 


New technology could lead to a new generation of electronic ingestible pills that could enable ways of monitoring patient health and treating disease. Image source:

need to come up with ways to power these ingestible systems for a long
time,” said research affiliate at the Koch Institute for Integrative
Cancer Research, Giovanni Traverso. “We see the 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.”

Traverso and one of the other authors of the study, MIT professor Robert
Langer, 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.

Langer believes this could lead to a new generation of
electronic ingestible pills that could someday enable novel ways of monitoring
patient health and treating disease. Currently the devices are powered by small
batteries, but conventional batteries self-discharge over time and pose a
safety risk. To overcome such disadvantages, Langer and Traverso worked with
Anantha Chandrakasan, head of MIT’s Department of Electrical Engineering, and
Philip Nadeau, the lead author of the paper. Both researchers specialize in
developing low-power electronics.

To begin, the team took inspiration from a simple type
of  volaic cell known as a lemon battery,
consisting of two electrodes — often a galvanized nail and a copper penny — stuck
in a lemon. The lemon’s citric acid carries a small electric current
between the two electrodes.

To replicate that strategy,
the researchers attached zinc and copper electrodes to the surface of the ingestible
sensor. The zinc emitted 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.

Next, the team tested their idea
in pigs. It took an average of six days for the device to travel through the
digestive tract, and while in the stomach, the voltaic cell produced enough
energy to power a temperature sensor and to wireless transmit the data to a
base station located two meters away, with a signal sent every 12 seconds. Once
in the small intestine, the cell generated only about 1/100 of what it produced
in the stomach.

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 its 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.

The new device could also be used for drug delivery. In the study, the researchers
demonstrated they could use the power generated by the voltaic cell to release
drugs encapsulated by a gold film. This could come in handy for doctors when
they need to try out different dosages of drugs, such as a medication for
controlling blood pressure.