A small battery can power an electronic device in the digestive system, then break down when it is no longer needed.
Ingestible electronic capsules already exist to observe or measure what is happening inside the body. Some can also transmit information or perform a temporary action. However, they need power. A conventional battery contains materials that are not designed to remain in the body and would normally have to be expelled without causing harm.
A bioresorbable battery integrated into an ingestible capsule breaks down in the stomach after use.
Credit: Courtesy of the researchers; MIT News — CC BY-NC-ND.
Researchers have therefore designed a battery whose main components can gradually disappear inside the body. It uses magnesium and molybdenum trioxide, among other materials, deposited on a paper substrate. The entire assembly is protected by materials suited to temporary residence in the digestive system.
The battery reaches a maximum voltage of 1.84 V. A version intended for capsules maintained a voltage of about 1.6 V during a day of continuous discharge. This performance is sufficient to power several small electronic functions without relying on a conventional battery.
The researchers notably integrated it into a capsule capable of sending a radio signal. This device makes it possible to track the passage of a capsule after it has been swallowed. During tests outside an organism, the signal could be correctly detected at a distance.
The devices were also tested in pigs, whose digestive system has dimensions similar to those of humans. One battery in particular remained operational in the stomach for three days. Other experiments verified radio transmission and electrical operation.
A device that passes quickly through the intestine can simply be eliminated naturally within a few days. In this case, components capable of breaking down mainly provide additional safety if the device remains stuck longer than expected.
Several points remain to be studied before considering uses in humans. Researchers must notably measure how long the batteries can be stored before use and their stability over extended periods. They also want to better control the thickness of their protective coating, which influences when the different components begin to break down.