Sweating profusely one second and generating electricity the next, what turns the human body into a generator?

The recent hot weather is really hot.

As soon as I go out, sweat starts dripping.

Most people are in a state of "not wanting to go to work" and "not wanting to leave work".

(Because it’s hot on the way to and from get off work!)

Sweat is a liquid secreted by sweat glands, which is composed of 98%-99% water. Humans and other higher animals sweat due to high external temperature, high-intensity exercise or nervous tension.

Sweating caused by heat stimulation due to increased external temperature or increased heat production in the body is called perceptual sweating. The sweating area is widely distributed, involving the skin of all parts of the body, especially the forehead, neck, front and back of the trunk, waist, back of the hands and forearms, followed by the neck, sides of the trunk and most of the limbs, and then the medial side of the thigh and armpits. The palms and feet sweat the least. In addition, mental tension can also cause sweating. The sweating centers are distributed in various parts of the central nervous system.

Sweat has the functions of cooling down, protecting the skin, and excreting waste from the body; however, overdeveloped sweat glands often cause distress to people: sticky sweat soaking clothes not only makes people feel uncomfortable, but may also emit an "unfriendly" odor.

But did you know that salty sweat can actually be used for another purpose? It can generate electricity.

That’s right, it’s electricity generated by sweat (not love).

Last year, researchers from the National University of Singapore created a thin film of nano-water-absorbing material that can quickly evaporate sweat from the skin. Even more cleverly, it also uses water-driven power generation technology to collect water from human sweat to power wearable electronic devices such as watches and fitness trackers.

Now, a research team from the University of Massachusetts Amherst (UMass Amherst) says that the new power-generating biofilm they designed is expected to revolutionize the wearable electronic device industry, providing long-term, continuous power for personal medical sensors, personal electronic devices, and more.

The relevant research paper, titled "Microbial biofilms for electricity generation from water evaporation and power to wearables", has been published in the scientific journal Nature Communications.

Figure ｜ The sensor driven by biofilm electricity is used to measure the mechanical signals generated by swallowing.

"This is a very exciting technology," said Xiaomeng Liu, a doctoral student in electrical and computer engineering at UMass Amherst's College of Engineering and lead author of the paper. "Unlike other so-called 'green energy', this is truly green energy."

According to the paper, the biofilm, which is about the thickness of a sheet of paper, is produced naturally by a modified strain of the bacterium Geobacter sulfurreducens (G. sulfurreducens).

In previous studies, Geobacter sulfurreducens has been used by scientists to generate electricity and has also been used in "microbial batteries" to power electrical equipment, but it still needs proper care and constant "feeding."

In contrast, this new biofilm can not only provide as much or even more energy as a battery of the same size, but can also work continuously without the need for "feeding".

"This biofilm is much more efficient," said Derek Lovley, distinguished professor of microbiology at UMass Amherst and co-corresponding author of the paper. "We radically reduced the amount of processing required to simplify the process of generating electricity. We continuously grow cells in the biofilm and then exploit the agglomeration of the cells. This reduces the energy input, makes everything much simpler, and expands the potential applications."

Figure｜Actual photo (left) and schematic diagram (right) of the new biofilm

So, what is the principle behind the new biofilm that uses moisture on the skin of organisms to generate energy?

First, Geobacter sulfurreducens is grown in colonies that look like thin mats, with each individual connected to the others by a series of natural nanowires. Second, a laser is used to etch small circuits into the film. Then, the film with the circuits etched on it is placed between electrodes and sealed in a soft, sticky, breathable polymer. Finally, energy is collected and converted to power small devices.

"This is a huge, untapped source of energy," said Jun Yao, professor of electrical and computer engineering at UMass Amherst and co-corresponding author of the paper.

When it is hot, especially in the hot summer, our skin surface is flooded with sweat, and the new biofilm can collect and convert the energy generated by the evaporation of sweat to provide power for small devices.

"Power supply has always been one of the limiting factors for wearable electronics," Yao said. "Batteries die and must be replaced or recharged. But they are bulky and uncomfortable." However, this transparent, small, thin and flexible biofilm can be attached directly to the skin like a Band-Aid, continuously generating stable electricity.

Figure | Integrated device arrays power small LCD screens.

In future work, the research team plans to increase the size of the biofilm to power more complex skin-wearable electronics. "Our next step will be to increase the size of the film to power more complex skin-wearable electronics, or even to power entire electronic systems instead of individual devices ," the research team said.

Reference Links:

https://www.nature.com/articles/s41467-022-32105-6