As the world looks towards renewable energy to reduce the negative impact of fossil fuels, some are turning to unlikely sources, such as sweat.

Researchers from the National University of Singapore (NUS) have created a material that helps evaporate sweat from our skin while harvesting the moisture from human sweat to power wearable electronic devices, such as watches and fitness trackers.

The material is a new type of film that absorbs sweat effectively, and could possibly be used in shoe insoles, shoe linings, and underarm pads.

The two main components of the novel thin film are cobalt chloride and ethanolamine.

Harvesting energy from sweat

When exposed to sunlight, the film can rapidly release water and it can be ‘regenerated’ and reused for more than 100 times.

The technological breakthrough was published in scientific journal Nano Energy in September last year.

The research team behind the invention consists of Professor Ding Jun, Assistant Professor Tan Swee Ching, NUS Doctoral Student Yang Jiachen, Post-doctoral Research Fellow Zhang Xueping, and NUS Doctoral Student Ramadan Borayek.

Beyond the function of absorbing water, the team has also designed a wearable energy-harvesting device comprising eight electrochemical cells, which generates electricity upon absorbing moisture.

Research team leader Tan, who is from the NUS Department of Material Science and Engineering explained:

“Sweat is mostly composed of water. When water is evaporated from the skin surface, it lowers the skin temperature and we feel cooler. In our new invention, we created a novel film that is extremely effective in evaporating sweat from our skin and then absorbing the moisture from sweat. We also take this one step further - by converting the moisture from sweat into energy that could be used to power small wearable devices."

Each electrochemical cell can generate about 0.57 volts of electricity in the presence of moisture.

The overall energy harvested by the device is sufficient to power a LED light.

This proof-of-concept demonstration illustrates the potential of battery-less wearables powered using human sweat.

A promising alternative to conventional moisture-absorbing materials

Compared to moisture-absorbing materials that already exist, such as silica gels, which are often found in packaging of food and clothing items to absorb moisture.

Currently, conventional moisture-absorbing materials absorb a low amount of water and are bulkier, making them unsuitable for absorbing sweat.

In comparison, the new moisture-absorbing film developed by NUS researchers takes in 15 times more moisture and do this 6 times faster than conventional materials.

In addition, the innovative film made by the team at NUS can change colour upon absorbing moisture, from blue to purple, and finally pink.

This colour-changing feature can be used an indicator of the degree of moisture absorption.

The research team also successfully demonstrated the use of the film in breathable and waterproof polytetrafluoroethylene membranes in the form of an underarm pad, shoe lining and shoe insole.

A prototype for the shoe insole was created using 3D printing, according to Ding.

Tan said how these applications could improve personal comfort:

“Underarm sweating is embarrassing and frustrating, and this condition contributes to the growth of bacteria and leads to unpleasant body odour. Accumulation of perspiration in the shoes could give rise to health problems such as blisters, calluses, and fungal infections. Using the underarm pad, shoe lining and shoe insole embedded with the moisture-absorbing film, the moisture from sweat evaporation is rapidly taken in, preventing an accumulation of sweat and provides a dry and cool microclimate for personal comfort.”

The next step for the researchers is to work with companies to incorporate the novel moisture-absorption film into consumer products.

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Photos by National University of Singapore