Electronics Kombucha? Sure, why not?

Inexpensive, lightweight, flexible yet robust circuit boards are critical for wearable electronics, among other applications. In the future, those electronics could be printed on flexible circuits made from bacterial cultures used to make the popular fermented black tea drink known as kombucha, according to a recent paper posted to the preprint server arXiv.

As we previously reported, for kombucha it is only necessary to combine tea and sugar with a kombucha culture called SCOBY (symbiotic culture of bacteria and yeast), aka the “mother” – called tea mushroom, tea fungus, or a. Manchurian mushroom. It’s like a sourdough starter. A SCOBY is a firm, gel-like collection of cellulose fiber (biofilm), courtesy of the active bacteria in the culture that creates the perfect breeding ground for yeast and bacteria to thrive. Dissolve the sugar in boiling non-chlorinated water, then add a few tea leaves of your choice to the hot sugar water before discarding.

When the tea cools, add the SCOBY and pour the whole thing into a sterilized beaker or jar. Then cover the beaker or jar with a paper towel or cheesecloth to keep out insects, let it sit for two to three weeks, and voila! You have your own home brewed kombucha. A new “daughter” SCOBY will float right at the top of the liquid (technically known in this form as a pellicle).

Aside from the popularity of the drink, kombucha cultures hold promise as a useful biomaterial. For example, in 2016, an Iowa State apparel, merchandising and design professor named Young-A Lee drew attention to her proof-of-concept research on using dried SCOBYs as a sustainable leather substitute for SCOBY-based biodegradable clothing, shoes, or handbags. In 2021, scientists at the Massachusetts Institute of Technology and Imperial College London created new types of tough “living materials” that could one day be used as biosensors, helping to clean water or detect damage to “smart” packaging materials . Experiments last year by researchers at Montana Technological University (MTU) and Arizona State University (ASU) showed that membranes grown from kombucha cultures were better at preventing biofilm formation – a significant challenge in water filtration – than current commercial membranes.

“Today kombucha is emerging as a promising candidate for producing sustainable textiles for use as environmentally friendly bioengines,” co-author Andrew Adamatzky, from the University of the West of England in Bristol told New Scientist. “We will see dried – and hopefully live – kombucha mats incorporated into smart wearables that extend the functionality of clothing and gadgets. We plan to develop a smart eco-wear that will be a convergence of dead and living biological material.”

Adamatzky previously co-authored a 2021 paper showing that live kombucha mats exhibited dynamic electrical activity and stimulus responses, as well as a paper last year describing the development of a reactive bacterial glove to serve as a live electronic sensing device. Inspired by the potential of kombucha mats for wearable electronics, he and his latest co-authors have now demonstrated that it is possible to print electronic circuits on dried SCOBY mats.

The team used kombucha bacteria from commercial sources to grow their mats, and then air-dried the cultures on plastic or paper at room temperature. The mats do not tear easily and are not easily destroyed, even when immersed in water for several days. One of the test mats even survived oven temperatures of up to 200°C (392°F), although the mats will burn when exposed to an open flame. Adamatzky et al. they were able to print conductive polymer circuits on the dried kombucha mats with an aerosol jet printer and also successfully tested another method of 3D printing a circuit from a conductive polyester/copper mix. They could even attach small lights to the circuits with epoxy glue spiked with silver, which still functioned after being bent and stretched several times.

According to Adamatzky et al., unlike the live kombucha mats he’s worked with before, the dried SCOBY mats are non-conductive, allowing electrical current to pass through the printed circuit. The mats are lighter, cheaper and more flexible than the ceramic or plastic options. Possible applications include wearable heart rate monitors, for example, and other kombucha-based devices. “Future research will involve printing high-level functional circuits, capable of sensing – and possibly recognizing – mechanical, optical and chemical stimuli,” the authors said.

DOI: arXiv (preprint), 2023. 10.48550/arXiv.2302.03984 (About DOI).