The 1.84-volt paper battery (the brown circle structure in the bioabsorbable radio-frequency identification device capsule shown here) was tested in pigs. [Photo courtesy of Mehmet Girayhan Say/MIT]
The researchers said bioresorbable batteries could make ingestible medical devices safer for patients and minimize the environmental impact of batteries after excretion.
“For many of the systems we’re developing, we need power, and we power the system through different ways,” Giovanni Traverso, senior author of the research paper published in Nature Chemical Engineering, said in an MIT news release. “Often, we use batteries, so the question here was: Could we develop a battery that was bioresorbable, and then apply that across a range of application areas?”
Ingestible medical devices typically rely on transmitted external power sources or coin batteries. These batteries often contain lithium, silver oxide and other metals that pose a safety risk or release toxic materials if the ingested device and outer casing break or the battery leaks.
Traverso and his team determined their battery needed to include metals that could act as electrodes but were also safe for human consumption.
“We were highly restricted in what materials to use,” he told Nature.
They chose magnesium for the battery’s anode and molybdenum trioxide for its cathode, since the two are metallic micronutrients the body needs and could consume in small amounts. Together, magnesium and molybdenum trioxide can produce a voltage high enough to power small devices. Traverso and his team chose an ionic liquid gel for its electrolyte.
“Those materials are known to be relatively safe,” Traverso said. “That was the biggest driver, thinking about materials that can be tolerated by humans.”
Inspired by edible candy wrappers made of rice paper, the battery’s outer packaging consists of a cellulose-based coating dipped in beeswax that supports the battery without affecting electrical performance. The beeswax slows down the effects of stomach acid by preventing thermal damage to the gel electrolyte and provides short-term protection for the battery. Over time, the entire battery dissolves.
The researchers designed a 7.5 mm disc version of the battery (top) and a 24 mm rectangular bar version (bottom) for various future applications. [Image courtesy of MIT]
Testing the batteries
The researchers tested how the batteries would behave in the GI tract by exposing the devices to a highly acidic solution to mimic gastric juice.The batteries functioned normally for about three days before performance declined. The batteries came apart within a few weeks and completely dissolved after several months.
The team then tested the battery in a degradable electrical stimulation device they developed in 2023. The device delivers an electrical current to the stomach lining, stimulating endocrine cells to increase levels of the hunger hormone ghrelin. Ghrelin secretion stimulation could help treat symptoms such as nausea, loss of appetite and body mass loss that occur in patients with cancer, cachexia and other chronic illnesses.
In the study, the battery powered continuous electrical stimulation for up to three days.
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The then researchers tested the batteries in pigs with ingestible, bioresorbable radio-frequency identification (RFID) devices that transmit data from inside the body to an external source.
Battery-assisted RFID systems often use coin cell batteries to power the ingestible device in tracking and patient monitoring for medication adherence. RFID tags with the investigational battery could transmit continuously from the GI tract for up to 1.5 meters, a longer range than traditionally powered tags, the study showed.
Travers and his team are planning how to test the biodegradable RFID devices powered by their bioresorbable battery in humans. He said they hope to start human testing in less than two years.
“What makes this work exciting is that we were able to show that a bioresorbable battery is not just a concept,” said Mehmet Girayhan Say, the paper’s lead author. “It can actually power clinically relevant functions inside the gastrointestinal tract and then simply dissolve.”
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