Ingestible electronic devices have come along in leaps and bounds in recent years, and capsules that patients swallow are now able to take live images of the gastrointestinal (GI) track, deliver drugs and monitor parameters like pH, temperature, pressure and heart rate. However, powering these devices for periods of more than a few hours is still a challenge. Many current devices still rely on primary cell batteries, many of which contain toxic materials.

In recent years, devices made from complementary metal-oxide semiconductors (CMOS) have become less power-hungry, now only using nanowatts of energy thanks to advanced device designs and improvements in technology. Advances in materials, design and packaging have also allowed researchers to make safe gastric devices that are small enough to be swallowed and which then unfold after being ingested. These structures can remain in the stomach for up to seven days. Biocompatible galvanic cells and even “transient” electronics that disappear once their work is done are making progress too.

Biocompatible galvanic cells

A team led by Giovanni Traverso of the Massachusetts Institute of Technology (MIT) and Harvard Medical School has been focusing on biocompatible galvanic cells and is now reporting on a device that can harvest energy in the GI tract. The new system, which is made from commercial semiconductor parts, is fully autonomous and can monitor temperature inside the body (in this case a pig) and wirelessly send data to an external receiver. The device can even exploit the harvested power to activate drug release by dissolving gold membranes covering wells on a model device.

“Our bio-galvanic cell consists of a redox couple formed by a dissolving metallic anode that undergoes galvanic oxidation and an inert cathode that returns electrons to the solution,” explains Traverso. “In our case, the gastric or intestinal fluid actually forms the electrolyte – rather like the lemon battery often studied in high-school science classes. This fluid serves as the electrolyte with copper and zinc serving as the cathode and anode respectively.

Applications in diagnosis and treatment

“The system can harvest energy over several days from the GI tract, and could thus be applied to a broad set of applications for diagnosis and treatment,” Traverso tells The device we have fabricated could be used to evaluate core body temperature and for evaluating GI transit time, given the differential temperature between the body and the external environment.”

He mentions a specific application: “A recent study evaluating data collected from more than 8000 patients found that peripheral temperature readings were not accurate enough to help physicians make clinical decisions, so continuous automated central temperature measurements via a wireless ingestible system like ours may provide significant benefit in such a context.”

Whole new set of ingestible electronic systems

The team, which includes researchers from the KTH Royal Institute of Technology in Stockholm, is now interested in coupling systems like these with other technologies it is developing that allow the devices to stay in the GI tract even longer. “We are also developing a series of new sensors that can sense a broad set of physiological and pathophysiological signals for early detection of disease,” says Traverso. “Coupled with drug delivery, we envision the development of a whole new set of ingestible long-term resident electronic systems.”

“There is also room to improve the battery chemistry, which may lead to dramatically improved performance and smaller size”, adds team member and lead author of the study Phillip Nadeau of MIT.

The ingestible device is detailed in Nature Biomedical Engineering doi:10.1038/s41551-016-0022.