Wearables have been around for a few years but their popularity, especially in the form of smartwatches and fitness trackers, has taken off. For health and fitness tracking, these devices are becoming increasingly valuable. However, there’s one drawback; as wearables need battery to operate, they need regular recharging. Now, scientists are looking for natural ways to recharge these devices and they found one – sweat. Devices powered this way could be so small that you’ll forget they are there.
Several research facilities around the world have dedicated their time in developing new ways to use sweat as an energy source for wearable devices. UC-San Diego and Glasgow University are two such institutions.
UC San Diego’s The Center for Wearable Sensors has world-renowned faculty and top students working in the key areas that converge to invent and test the sensing platforms and technologies that fuel the future of sensor systems. Certain chemicals found in human sweat can be used as fuel in wearable-size fuel cells. “A fuel cell consists of two electrodes—an anode and a cathode—with an electrolyte between them. The fuel goes into the anode, where a catalyst separates its molecules into electrons and protons. Sweat isn’t just water. It contains trace amounts of a wide variety of minerals and other substances like glucose and lactate. These substances, called metabolites, are by-products of the chemical processes that constantly go on inside living beings, and they make attractive biofuels,” reports IEEE Spectrum.
Researchers at the University of Glasgow have developed a new type of flexible supercapacitor which replaces the electrolytes found in conventional batteries with sweat. It can be fully charged with as little as 20 microliters of fluid and is robust enough to survive 4,000 cycles of the types of flexes and bends it might encounter in real-world use, University of Glasgow reported in May. The system works by coating polyester cellulose cloth in a thin layer of a polymer known as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate – or PEDOT: PSS. The team chose the polyester cellulose cloth because it is particularly absorbent, and PEDOT: PSS because it offers a useful combination of flexibility, high conductivity and environmental friendliness. The PEDOT: PSS acts as the supercapacitor’s electrode. As the cloth absorbs its wearer’s sweat, the positive and negative ions in the sweat interact with the polymer’s surface, creating an electrochemical reaction which generates energy.
Our body produces sweat when we exert energy. Hence, it’s an excellent choice for powering wearable fitness trackers. But there are other ways sweat can be used in wearables. Wearable sweat sensors for monitoring biomarkers for chronic health conditions are of significant commercial interest. UC San Diego researchers have developed flexible sensors that can be worn on the skin to sensitively track vitamin C levels in sweat. The device could be useful for people to track their daily nutritional intake and dietary adherence.