(Nanowerk Spotlight) Inside the human digestive tract, an electronic capsule can now generate its own electricity using recycled seaweed, power small electronic devices, with the duration depending on the specific energy requirements of each device, kill harmful bacteria through electrical pulses, and then breaks down into fragments that undergo further decomposition by gut bacteria and reintegrate into the natural environment.
This advance in bioelectronics emerged from an unlikely source: the nanofibers inside common sargassum seaweed.
The ability to safely power medical devices inside the body has remained elusive despite rapid advances in miniature electronics. Standard batteries contain toxic metals and electrolytes that pose serious health risks if they leak. Implantable power sources typically require surgical procedures for both insertion and removal. While researchers have attempted to create safe alternatives using everything from sugar to mechanical energy harvesters, these approaches have fallen short – producing either insufficient power or requiring components that the body cannot break down naturally.
A team at the University of Science and Technology of China has now demonstrated that seaweed-derived materials can form the basis of a powerful, fully digestible energy source. Their supercapacitor harnesses the unique properties of cellulose nanofibers extracted from sargassum seaweed using only food-grade processing methods.
At the heart of the device are electrodes made from an intricate network of seaweed-derived nanofibers, each just 20-30 nanometers in diameter. These nanofibers are combined with nanoscale activated carbon particles (processed through high-speed ball milling) to create a highly conductive material with an extensive surface area for storing electrical charge. The same nanofibers also form a separator between the electrodes, while edible gold leaf serves as the current collector. Food-grade beeswax encases these components, and the entire device fits inside a special capsule designed to dissolve in the intestines.
Fabrication and application of the fully ingestible supercapacitor. a) Photograph of food-grade ingredients and schematic of the preparation process of SCNF-based electrode and separator. SCNF and AC solutions form SCNF-based electrodes and separators during the filtration process. b) A symmetric supercapacitor assembled with SCNF-based electrodes, separator, and Au foil. c) Schematic of the whole process of swallowing the supercapacitor into the human tissues and electrical stimulation for bacteriostasis during the self-discharge process. (Image: Reprinted with permission by Wiely-VCH Verlag) (click on image to enlarge)
The performance metrics set this device apart from previous biodegradable power sources. It achieves an electrode capacitance of 2.29 farads per square centimeter – roughly ten times higher than similar digestible energy storage devices. The energy density reaches 307 microwatt-hours per square centimeter, sufficient to power small sensors and drug delivery systems for several hours.
Testing in simulated digestive conditions revealed an unexpected benefit: the electrical discharge naturally generated by the device kills bacteria. When exposed to E. coli, the supercapacitor can eliminate nearly 100% of bacterial cells within 10 minutes through electrical stimulation alone. This antibacterial effect occurs during the device’s normal operation, requiring no additional components or modifications.
The researchers extensively tested the safety of their seaweed-derived materials. When exposed to human gastric mucosal cells for 24 hours, the nanofibers showed minimal toxicity, with over 93% of cells remaining viable compared to control groups. After completing its useful life, the device breaks down into small fragments. These fragments can be further decomposed by gut bacteria into basic nutrients – much like digesting seaweed in its natural form.
This technology maps directly to several immediate medical applications. The supercapacitor could power capsule endoscopes that image the digestive tract, sensors that monitor gut conditions over time, or smart drug delivery systems that release medication at specific locations. The built-in antibacterial capabilities add another therapeutic dimension, potentially allowing the power source itself to help treat infections.
The combination of food-grade materials, sufficient power output, and complete digestibility represents a significant step toward practical ingestible electronics. However, important challenges remain. The researchers must now optimize the device’s power duration, verify its safety through clinical trials, and develop standardized manufacturing processes. The technology also needs integration testing with various medical devices to validate its real-world utility.
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