Researchers from the Massachusetts Institute of Technology have created a biodegradable and ingestible paper battery designed to power temporary medical devices inside the digestive tract. The prototypes were tested on pigs, as reported in the journal Nature Chemical Engineering and by Live Science. The experiments showed that the batteries could supply energy to various electronic devices for about three days before gradually losing their power. This could lead to new medical technologies such as sensors for detecting internal bleeding, systems for delivering drugs, or devices that stimulate tissues and organs without the need for traditional batteries that are hard to remove from the body. The technology was developed by a team led by Professor Giovanni Traverso from MIT. The battery is made from a thin, porous paper, partly composed of cellulose nanofibers that act as a binder. One of the key materials is magnesium-molybdenum trioxide (Mg-MoO₃), which dissolves slowly in the acidic environment of the digestive system. Unlike conventional batteries, which must be isolated to prevent leakage, this new battery is designed to degrade gradually within the body. The researchers also used a wax-based coating to slow down the degradation process when exposed to digestive fluids. Some versions include an additional layer of candelilla wax, which helps extend the battery's operating time. This coating is crucial in controlling the degradation rate and, therefore, the length of time the battery can provide electricity. The scientists created two versions of their paper battery. In laboratory tests, the smaller model produced a voltage of approximately 1.77 volts, with a capacity of 2 mAh per square centimeter. The larger model reached about 1.84 volts and had a maximum capacity of 3.5 mAh. To test how the batteries would function in real conditions, the researchers placed them in 3D-printed capsules and administered them to pigs orally using an endoscope. Both models continued to generate electricity for about three days, but their power levels gradually decreased. The larger battery, for instance, saw its voltage drop from about 1.8 V to 1.6 V after one day and to about 1.45 V after three days. The smaller version experienced a similar decline, going from about 1.7 V to 1.35 V over the same period. The researchers also demonstrated that their battery could power electronic components placed inside the body. During the experiments, it was used to power an RFID tag placed in a pig's esophagus and a circuit designed for electrical stimulation. The RFID tag allowed the detection of drug administration and transmitted the information to a receiver located up to 1.5 meters away. John Rogers, a materials scientist and pioneer in bioelectronics at Northwestern University, found this demonstration particularly interesting. Although he was not involved in the study, he praised the system's stability as it passed through the digestive tract of a large animal. However, he also pointed out certain limitations. While the battery uses several biodegradable components that break down within the body, the electronic circuit used in the experiments was not fully biodegradable and was naturally expelled with the pig's feces. For the researchers, one of the main challenges now is to control the battery's lifespan more precisely and make its degradation process more predictable.