A small prototype paper battery that eventually breaks down inside the body was functional for at least three days in a trial in pigs, report researchers from MIT.
This is an early stage study, and the technology still needs to be refined, but when perfected it could be used to power devices used for therapy, diagnostics, or drug monitoring, among others.
“Ingestible and implantable electronics are revolutionizing healthcare… These systems typically rely on primary or secondary batteries for power; however, conventional batteries, such as alkaline and lithium-ion batteries, pose serious risks when used inside the body,” write lead author Giovanni Traverso, MD, PhD, a professor at MIT, and colleagues in Nature Chemical Engineering.
“Packaging failures and electrochemical side reactions can lead to toxic leakage, tissue damage or gas formation, whereas nondegradable casings contribute to electronic waste and environmental hazards.”
In this study, Traverso and colleagues built thin paper batteries, a cellulose-based supporting material, a relatively biocompatible electrolyte and protective natural wax coatings. The electrodes use magnesium and molybdenum compounds, which are less toxic than conventional batteries. When they corrode, they mainly form magnesium ions, magnesium hydroxide and molybdate compounds, which the body can absorb and clear through established pathways.
The batteries were tested in the lab and in pigs. They powered two prototype applications: a radio-frequency identification tag intended to confirm that medication had been swallowed, and a capsule that electrically stimulated the stomach. The researchers studied battery performance, device breakdown, movement through the gut and also looked at whether the batteries caused tissue damage.
The battery-assisted tag communicated over four meters in air and remained detectable from 1.5 meters when placed in pigs’ esophagi. Swallowing the tag produced a roughly 10-decibel signal change, which the team believe could allow ingestion to be recorded remotely.
The stimulation capsule delivered electrical pulses for up to three days with one battery. In pigs, 20 minutes of stomach stimulation increased blood concentrations of the hunger-related hormone ghrelin by an average of about 36%, without obvious tissue damage.
“Biodegradable capsule electronics offer a noninvasive solution for both wireless health monitoring and transient bioelectronic therapies. By bridging the gap between transient power sources and functional medical devices, this study lays the foundation for next generation smart ingestible platforms that align with the principles of sustainability, safety, and clinical practicality,” conclude the authors, although they caution that “several components and capabilities require further work before clinical translation.”
For example, the animal groups were small and had not eaten before the experiment, degradation was partly studied using accelerated laboratory conditions, and the circuit board and radio-frequency identification tag chip were not bioresorbable. Human use will require more consistent manufacturing, realistic gut testing and extensive safety studies, emphasize the researchers.
