Wearable devices only took off after the processors and batteries in them were both small and light enough to be comfortably worm However, batteries still need to be charged and can pose a health hazard in their own right. This is why there has been so much research to come up with ways to harness the body’s energy to power wearables. Work has been done to date to try to convert human body heat into energy and turn motion into energy. A novel experiment by Professor Seokheun Choi of Binghamton University of New York showed that health monitoring devices could be powered by human sweat, too.

E-skins or electronic skins are a new form of wearable electronics. It would lay against the skin. Depending on the design, it could monitor someone’s blood sugar, diagnose health problems, or deliver drugs through the skin. In every case, a stable power supply is essential. The solution was right at their feet, or in this case, under the e-skin.

Sweat includes salt, water, ammonia and organic substances. The organic substances and ammonia can be processed by bacteria. This is why bacteria readily grows in your sweaty clothes. This same residue could be processed by bacteria in a microbial fuel cell. The fuel cell would use the bacterial digestive process to generate a low, steady current. The bacteria oxidizes both organic and inorganic substances, creating a current. The current is transferred to an anode and flows to the cathode, a process similar to conventional batteries except for the substance inside said battery.

There are several benefits to this approach. One is that the device in theory could run forever. Another benefit is that patients with limited mobility or mental function never have to worry about trying to swap out batteries or otherwise maintain it. Unlike wearables that depend on human motion, every patient is generating a steady stream of sweat. This makes sweat-power ideal for wearable devices in biomedical applications. This isn’t a foolproof solution, though. The skin is a harsh environment. It is rather dry, and that can be made worse by sweat absorption. It is acidic, and that can damage electronics. It is relatively cool for bacterial fuel cells, and the temperature can plummet if the person’s skin is exposed to very cold air. The battery itself would have to limit oxygen exposure. Yet with every bend and flex of the underlying tissue, the fuel cell is strained and could break. A skin interface system may need to collect and store sweat to provide a steady stream of power, and that increases the size it needs to be.

While harnessing sweat for energy by wearable devices is still in the very earliest stages, it holds significant promise. The half million dollar grant Doctor Choi received is only funded the first phase of his research, and he plans to continue his work. He also continues in his role as the laboratory director and associate director of the Binghamton Center for Research and Advanced Sensing Technologies and Environmental Sustainability.