A sweat-activated, wearable microbial fuel cell for long-term, on-demand power generation

In this work, we enabled on-demand, long-functioning, sweat-based power generation through a wearable paper-based microbial fuel cell (MFC) using a novel spore-forming biocatalyst, Bacillus subtilis. The MFC is sustainable and survivable even in the extreme environmental conditions of human skin. B. subtilis, usually found on the skin, was able to form endospores that endure extreme dryness or nutrient limitation when sweat access was limited or unpredictable for humans at rest, offering long-term operation and stable storage. When human sweat was introduced, spore germination and gradual power generation were observed without adding nutrient germinants. Through repeated sporulation and germination depending on the sweat availability, B. subtilis provided a sustainable solution for an innovative sweat-activated power source that can result in the long-lasting vision of self-sustaining wearable electronics. Even after the 48-h operation, the device generated a maximum power density of 24 μW/cm² and a maximum current density of 175 μA/cm², which is comparable to or even higher than the previously reported paper-based MFCs using well-known strong exoelectrogens in an optimized bacterial medium. Furthermore, B. subtilis in sweat was shown to be commensal with other skin microorganisms while producing antibiotic substances that were effective against potential pathogens, exhibiting a great potential for seamless and intimate integration with skin-mountable applications.