MIT Redefines ‘Battery Acid’ with Low-tech Voltaic Cell Powered by Stomach Acid

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voltaic cell
Diemut Strebe | News.mit.edu

Ingestible medical devices are seen as the future of non-invasive procedures, able to deliver drug therapy and record medical data. Thus far, they have been powered by batteries that are costly, temporary, and sometimes risky. Now, MIT engineers have found a sustainable power source to run these artificial cells: stomach acid.

In recent years, advances in energy harvesting and wireless power transfer technologies have paved the way to considerable progress in the design of ingestible electronic devices, much like the voltaic cell produced by MIT engineers. From drug delivery systems, video capture devices, temperature and pressure sensors, to respiration and heart rate monitors, theses systems open up very promising prospects in diagnosis and treatment.

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However these ingestible systems rely on small batteries to function, and as such, they don’t last for long inside the body. The device will discharge and can be potentially harmful to the body.

Ingestible Voltaic Cell That Harvests Power From the GI Tract

A team of engineers from Brigham and Women’s Hospital and MIT designed a voltaic cell that uses gastric acid as a source of fuel. The voltaic cell, described in a paper published in Nature Biomedical Engineering, is a cylindrical device with two zinc and copper electrodes attached to its surface.

This system is based on the same principle of a “lemon battery” (or potato battery), the simple electrical battery that’s very popular among kids for school experiments and science fair projects.

Given the fact that ingestible items travel through the GI tract, researchers wanted to use the acidic environment to power devices. In the same way that citric acid carries electric charges between the penny (copper) and nail (zinc), gastric acid acts as an electrolyte, generating enough power to run the voltaic cell.

The team tested the method with an ingestible thermometer fed to pigs and then recorded the signal from the transmitter, which came at a frequency of 900 MHz.

While in the stomach, the thermometer signal came every 12 seconds and spread over a distance of two meters. Then, when the capsule naturally traveled from the stomach into the small intestine, where the acidity is not as high, the device power fell. It still sent signals, though not as often.

The circuit is large at 40 mm long and 12 mm in diameter, but researchers said they would make it one-third of that size and then integrate the system to different types of sensors.

This latest development will extend the longevity and safety of these systems as well as reduce the cost of powering them. Hopefully, this will lead to a wider deployment of ingestible medical systems for various purposes.

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