Researchers have created a battery that can be swallowed to power medical devices inside the gastrointestinal tract and then degrade naturally, potentially eliminating the need to retrieve conventional batteries from the body. The technology, tested in pigs, operated for up to three days before its biodegradable components began to break down, according to a study published Monday, September 21, in the journal Nature Chemical Engineering.
Ingestible medical devices can be used for a range of purposes, from detecting bleeding and delivering drugs to stimulating specific tissues or organs. However, conventional batteries for such devices pose challenges: they are often too large, and their components must be isolated to prevent internal materials from contacting tissues and causing injury. The new battery is made from materials that degrade progressively in the acidic environment of the gastrointestinal tract and, according to the researchers, can be absorbed without leaving dangerous fragments or toxic byproducts.
The battery is constructed in multiple layers. The anode, or negative terminal, is made from a magnesium alloy, while the cathode contains molybdenum trioxide and activated carbon. Between them is a biodegradable electrolyte that enables the production of electric current. The researchers used cellulose nanofibers to create a thin, porous structure resembling paper. Giovanni Traverso, co-author of the study and director of the Laboratory for Translational Engineering at MIT, explained that this structure contributes to the battery's strength and degradation control, as well as its ability to produce energy.
To prevent the battery from being destroyed too quickly by gastric acid, the researchers coated it with beeswax. Some prototypes received an additional layer of candelilla wax for longer protection. Traverso said the wax layer is an essential design element because it allows control over how long the battery remains functional. The team built two versions. The smallest could be inserted into a standard gelatin capsule and produced approximately 1.77 volts, with enough capacity for low-power electronic devices. The larger version reached about 1.84 volts and a maximum capacity of 3.5 milliampere-hours. However, the researchers caution that performance needs improvement. Reza Ghodssi, a professor at the University of Maryland who was not involved in the study, believes that a capacity roughly ten times greater would make the technology much more promising.
For animal experiments, the prototypes were placed in 3D-printed capsules and administered to pigs using an endoscope. Both versions continued to function for up to three days, although their voltage and capacity gradually declined as the batteries degraded. The researchers used the smaller battery to power an experimental RFID tag placed in the esophagus. The system could communicate wirelessly with a receiver up to 1.5 meters away and allowed scientists to detect when the animal swallowed a medication. The larger battery powered a capsule that electrically stimulated the stomach. The experiment led to an increase in ghrelin levels, a hormone involved in stimulating hunger, without the researchers observing tissue damage in the stimulated area. The device used in the experiment is experimental, however.
One important caveat is that while the battery and its biodegradable components broke down, the electronic circuit board used in the gastric stimulation experiment was not bioresorbable. It was eliminated naturally by the animals. John Rogers, a researcher in bioelectronics at Northwestern University who was not involved in the study, noted that making all components from bioresorbable materials could eliminate the risk of part of the device becoming stuck in the gastrointestinal tract.
The technology is still in an experimental phase. One of the main challenges is achieving more precise control over how long the battery operates and when it begins to degrade. The researchers also found performance differences between batteries, associated with factors such as contact between layers, electrolyte distribution, and wax layer thickness. The team is now working to standardize the manufacturing process and adapt the coating so that batteries can be designed for operating periods ranging from a few hours to several days. Next steps include longer tests under conditions that more closely replicate the human gastrointestinal tract. According to Traverso, the researchers are working toward a first clinical study of the RFID system, which could begin in about two years. Until then, the results do not demonstrate that the battery is safe or effective for human use. The experiments reported in the current study were conducted on animals.