A battery that requires feeding instead of charging? This is precisely what scientists have accomplished with their innovative 3D-printed, biodegradable fungal battery. This living battery could provide power to sensors used in agriculture or research in remote places. When it has completed its function, it will digest itself internally.
Fungi are truly intriguing. This unique kingdom of life is more closely related to animals than to plants and includes a vast array of organisms. You can find everything from edible mushrooms and molds to single-celled creatures and the largest organism on Earth, as well as pathogens that can cause disease alongside curing agents for medicines. Now, researchers at Empa have harnessed another skill of fungi: generating electricity.
As part of a three-year project funded by the Gebert Rüf Stiftung under their Microbials program, scientists from Empa’s Cellulose and Wood Materials laboratory have created a functional fungal battery. While the living cells don’t generate a large amount of electricity, they produce enough to power temperature sensors for several days. Such sensors are useful in agriculture and environmental research. The most significant advantage of the fungal battery is that, unlike traditional batteries, it is completely safe and biodegradable.
Fungi from the printer
Technically, this cell is not a battery in the conventional sense but is referred to as a microbial fuel cell. Like all living organisms, microorganisms transform nutrients into energy, and microbial fuel cells capture some of that energy as electricity. Until now, these fuel cells have primarily relied on bacteria. “For the first time, we’ve utilized two different types of fungi to create a working fuel cell,” explains Empa researcher Carolina Reyes. The two fungal species work well together: a yeast fungus on the anode side releases electrons through its metabolism, while a white rot fungus at the cathode produces a unique enzyme that allows electron capture and conduction out of the cell.
The fungi are not introduced to the battery after the fact; they are included in the cell from the beginning. The components of the fungal battery are crafted using 3D printing technology. This technique helps researchers arrange the electrodes to maximize accessibility for the microorganisms to obtain nutrients. The fungal cells are integrated into the printing material. Achieving this is no easy task; “Finding a medium that allows the fungi to thrive is challenging,” states Gustav Nyström, Head of the Cellulose and Wood Materials lab. “Additionally, the ink must be easy to extrude without damaging the cells, while also being electrically conductive and biodegradable.”
Microbiology meets electrical engineering
The researchers drew on their lab’s significant experience with 3D printing soft, bio-based materials to develop an appropriate ink made from cellulose. The fungal cells can use cellulose as a nutrient, aiding in the breakdown of the battery post-use. However, their main nutrient source consists of simple sugars that are added to the battery cells. “We can store these fungal batteries in a dry state and activate them on site by simply adding water and nutrients,” says Reyes.
Even though these resilient fungi can withstand dry conditions, working with living materials offered several challenges for the researchers. This interdisciplinary project integrates microbiology, materials science, and electrical engineering. To characterize the fungal batteries, microbiologist Reyes had to not only learn about electrochemistry but also modify those techniques for use with 3D-printing inks.
The researchers now aim to enhance the power and longevity of the fungal battery, while exploring various other fungi that could generate electricity. “Fungi remain largely unexplored and underutilized, particularly in materials science,” agree Reyes and Nyström.
