Biofilm generates continuous electricity from sweat

Researchers at the University of Massachusetts Amherst have figured out how to engineer a biofilm that harvests the energy in evaporation and converts it to electricity. This biofilm, which was announced in Nature Communications, could revolutionise the world of wearable electronics, powering everything from personal medical sensors to personal electronics. Xiaomeng Liu, a graduate student in electrical and computer engineering in UMass Amherst’s College of Engineering and the paper’s lead author, said the technology is very exciting. “It is real green energy, and unlike other so-called ‘green-energy’ sources, its production is totally green,” Liu said.

This biofilm — a thin sheet of bacterial cells about the thickness of a sheet of paper — is produced naturally by an engineered version of the bacteria Geobacter sulfurreducens. G. sulfurreducens is known to produce electricity and has been used previously in ‘microbial batteries’ to power electrical devices. But such batteries require that G. sulfurreducens is properly cared for and fed a constant diet. By contrast, this new biofilm, which can supply as much, if not more energy than a comparably sized battery, works continuously because it is dead. Because it is dead, it does not need to be fed.

Derek Lovley, Distinguished Professor of Microbiology at UMass Amherst and one of the paper’s senior authors, said the biofilm is much more efficient. “We’ve simplified the process of generating electricity by radically cutting back on the amount of processing needed. We sustainably grow the cells in a biofilm, and then use that agglomeration of cells. This cuts the energy inputs, makes everything simpler and widens the potential applications,” Lovley said.

The new biofilm makes energy from the moisture on your skin. Approximately 50% of the solar energy that reaches the earth goes towards evaporating water. Jun Yao, Professor of Electrical and Computer Engineering at UMass, and the paper’s other senior author, said this is a huge, untapped source of energy. Since the surface of our skin is constantly moist with sweat, the biofilm can ‘plug-in’ and convert the energy locked in evaporation into enough energy to power small devices. According to Yao, the limiting factor of wearable electronics has always been the power supply, as batteries can run down and need to be changed or charged. But a clear, small, thin and flexible biofilm that produces a continuous and steady supply of electricity and which can be worn like a Band-Aid — as a patch applied directly to the skin — solves all of these problems.

What makes this all work is that G. sulfurreducens grows in colonies that look like thin mats, and each of the individual microbes connects to its neighbours through a series of natural nanowires. The team then harvests these mats and uses a laser to etch small circuits into the films. Once the films are etched, they are sandwiched between electrodes and sealed in a soft, sticky, breathable polymer that can be applied directly to the skin. Once this battery is ‘plugged in’ by applying it to the body, it can power small devices.

Researchers are now aiming to increase the size of the films to power more sophisticated skin-wearable electronics. Liu said that one of the goals is to power entire electronic systems, rather than single devices. This research was supported by the Institute for Applied Life Sciences (IALS) at UMass Amherst, which combined deep and interdisciplinary expertise from 29 departments to translate fundamental research into innovations that benefit human health and wellbeing.

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