MIT and Brigham and Women’s Hospital researchers have announced an ingestible device innovation: a small voltaic cell that can withstand the acidity of fluids in the stomach and still transmit information to a base station.
The small device can stay in the gastrointestinal tract for long periods of time and can produce enough power to operate small sensors or drug delivery devices. Researchers say that this power is a safer and cheaper alternative to the batteries that are used to power devices now.
“We need to come up with ways to power these ingestible systems for a long time,” Giovanni Traverso, a research affiliate at the MIT’s Koch Institute for Integrative Cancer Research, said in an MIT news release. “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.”
This is not the first time Traverso has created an ingestible device. He and his colleague MIT professor Robert Langer previously created an ingestible sensor that could monitor vital signs like heart and breathing rates from the digestive track.
The research team used the idea of a lemon to create a battery for the sensors that was low-powered and could safely discharge over time.
Lemon batteries have two electrodes (usually a galvanized nail and a copper penny) stuck into a lemon. The citric acid from the lemon allows a small electrical current to flow between the electrodes. Using this idea, the researchers attached zinc and copper electrodes to the ingestible sensor they created. The stomach acid receives the zinc ions and powers the voltaic current. The current produces enough energy to power a commercial temperature sensor and a 900 mHz transmitter.
Researchers tested these sensors in pigs and found that it took 6 days for the sensor to travel through the digestive tract. During that time, the sensor was able to wirelessly transmit the data to a base station that was 2 meters away and emitted a signal every 12 seconds from within the stomach.
After it moved to the small intestine, the sensor produced 1/100th of the power that it did 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 device prototype is shaped like a cylinder and is 40 mm long and 12 mm in diameter. The researchers hope they can reduce the size of the capsule and make it about one-third of its current size and could still carry the energy harvester, transmitter and small microprocessor.
“A big challenge in implantable medical devices involves managing energy generation conversion, storage and utilization. This work allows us to envision new medical devices where the body itself contributes to energy generation enabling a fully self-sustaining system,” said Anantha Chandrakasan, head of MIT’s Department of Electrical Engineering and Computer Science and one of the senior authors on the study.
These devices also have the potential to be used for drug delivery. The researchers were able to use the power generated by the voltaic cell to release drugs that were enclosed by a gold film. Doctors could use this method for administering different dosages of drugs like blood pressure control medication.
The research was funded by Texas Instruments, the Semiconductor Research Corp.’s Center of Excellence for Energy Efficient Electronics, the Hong Kong Innovation and Technology Commission, the National Institutes of Health and the Max Planck Research Award. It was published online in the Nature Biomedical Engineering journal.
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