Edible, Biodegradable Battery Could Power Swallowable Medical Devices

A battery made from materials similar to edible rice paper could power swallowable electronic medical devices. After the battery is safely digested, its broken-down components are absorbed by the body.

The tiny power supply has so far been tested in pigs, but it could eventually power ingestible devices that monitor human health or implantable devices that deliver electrical impulses to treat disease.

The researchers tested the battery in two medical devices. One contained a radio frequency identification (RFID) tag that transmitted data from inside the body. The other electrically stimulated the stomach to trigger the release of hormones that regulate hunger. Their findings are described in Nature Chemical Engineering¹.

Why biodegradable batteries could make ingestible devices safer

Traditional batteries can be dangerous if an ingested medical device breaks and the battery leaks, says Giovanni Traverso, a mechanical engineer at the Massachusetts Institute of Technology in Cambridge and a co-author of the study. Leaking batteries can cause chemical burns and release toxic substances as they pass through the digestive system.

Traverso and his colleagues therefore wanted to develop a battery made from non-toxic materials that could be absorbed by the body and would be less likely to cause injury.

“We were very limited in the materials we used,” says Traverso.

Batteries typically contain electrodes that store chemical energy, an electrolyte that carries charge between the electrodes and packaging that holds the components together. Lithium-ion and alkaline batteries can contain toxic metals, organic electrolytes that accumulate in the body and plastic casings that could shatter into sharp pieces.

Edible materials power the battery

Traverso’s group chose magnesium trioxide and molybdenum trioxide as the electrodes. Magnesium and molybdenum are metal micronutrients needed by the body in small amounts. When combined in a battery, they provide enough voltage to power electronic devices.

The researchers used a biodegradable ionic liquid as the electrolyte instead of the buffered saline used in previous biocompatible battery designs, which provided poor performance.

The packaging was also crucial. It needed to support the battery’s other components without reducing performance through electrical insulation. It also had to provide a large surface area and be made from a material that the body could safely absorb once the device was no longer needed.

“We were inspired in part by candies with edible rice paper wrappers,” says Traverso.

The battery’s cellulose-based coating dissolves over time, like a sweet wrapper. The entire battery is then soaked in beeswax, which slows the effects of stomach acid.

Battery dissolves inside the body

In simulated gastric fluids, the batteries began to break apart within two weeks and dissolved completely after a few months.

The researchers then placed each battery in a gel capsule with other fully biodegradable and non-toxic electronics before testing the system in pigs. An RFID tracking device inside a swallowable capsule sent a signal to a reader outside the pig’s body.

In a separate test, the researchers used endoscopy to place an electrical stimulation device in the pigs’ stomachs. The stimulation increased levels of the hunger hormone ghrelin.

Traverso, who is also a gastroenterologist, says such “electroceutical” devices are being investigated as a way to modulate communication between the gut and the brain. They could be less invasive than procedures such as bariatric surgery or implants that regulate digestive-system activity.