A paper-based battery powered a wireless tracking tag and a stomach-stimulation capsule in tests involving pigs. Made with magnesium and molybdenum trioxide, the cell is designed to break down after use, addressing a problem for temporary medical electronics that must work inside the digestive tract. Separate laboratory experiments examined its degradation; the study reports no human safety or treatment outcomes.
The battery has to meet two competing requirements: supply power while a device is working, then allow its materials to degrade. Its magnesium and molybdenum-trioxide electrodes generate current, with a paper separator and a gel electrolyte between them. Natural wax around the cell delays contact with stomach fluid. That protective layer gives the electronics time to operate before fluid exposure reduces the battery's performance.
To test that protection, the researchers anchored batteries in the stomachs of four pigs and retrieved them after up to three days. The capsule-size cells' average open-circuit voltage fell from about 1.7 volts initially to 1.35 volts on day three. Open-circuit voltage is measured without a device drawing power, so it shows that the retrieved cell retains an electrical potential; the application tests establish what the battery can actually run.
One application used radio-frequency identification, or RFID, to let an external reader detect a capsule. A battery-assisted tag placed in a pig's esophagus remained readable from 1.5 metres away. Its signal weakened on entering tissue, providing a way to detect ingestion under the controlled test conditions. The reader stayed in a fixed position; changes in body position and tag orientation could complicate that signal in everyday use.
A second capsule used the battery to deliver electrical pulses to the stomach. This animal experiment shows that the battery can power a stimulation system, but does not establish a treatment benefit for patients.
Degradation was studied separately in simulated stomach fluid. For the stimulation capsule, the researchers kept the fluid at body temperature, 37 degrees Celsius, for the first 14 days, then raised it to 75 degrees to accelerate the remaining test. The resulting breakdown cannot be read as a timetable for dissolution inside a person.
The devices also retain some conventional electronics: the stimulation capsule has a printed circuit board, and the tracking tag contains an RFID chip that does not resorb. The work therefore demonstrates a degradable power source within functioning experimental capsules, while the behaviour of the complete systems in people remains untested in this paper.
Sources
- Nature Chemical Engineering: Bioresorbable batteries for transient ingestible bioelectronics
- MIT News: Batteries that safely break down in the GI tract could improve ingestible devices
- Representative capsule-endoscope photograph by Euchiasmus, public domain. The photograph shows a conventional capsule endoscope, not the experimental battery or capsules.