Sweat Charging with Bio Batteries

LONDON: You may soon be able to charge your phone with your sweat. 


For the first time ever, scientists have found away to make human sweat power your small electronic devices. 

Researchers have designed a sensor in the form of a temporary tattoo that can both monitor a person's progress during exercise and produce power from their perspiration. 

The device works by detecting and responding to lactate, which is naturally present in sweat. 

Scientists have created a sweat-powered bio battery. Batteries produce energy by passing current, in the form of electrons, from an anode to a cathode. 

In this case, the anode contained the enzyme that removes electrons from lactate, and the cathode contained a molecule that accepts the electrons. 

When 15 volunteers wore the tattoo bio batteries while exercising on a stationary bike, they produced different amounts of power. 

Interestingly, people who were less fit (exercising fewer than once a week) produced more power than those who were moderately fit (exercising one to three times per week). 

Enthusiasts who worked out more than three times per week produced the least amount of power. 

The researchers say that this is probably because the less-fit people became fatigued sooner, causing glycolysis to kick in earlier, forming more lactate. 

The maximum amount of energy produced by a person in the low-fitness group was 70 microWatts per cm2 of skin. 

Wenzhao Jia from University of California San Diego said: "The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices. Right now, we can get a maximum of 70 microWatts per cm2, but our electrodes are only 2 by 3 millimeters in size and generate about 4 microWatts — a bit small to generate enough power to run a watch, for example, which requires at least 10 microWatts. So besides working to get higher power, we also need to leverage electronics to store the generated current and make it sufficient for these requirements.'' 

"Lactate is a very important indicator of how you are doing during exercise," says Jia. 

In general, the more intense the exercise, the more lactate the body produces. During strenuous physical activity, the body needs to generate more energy, so it activates a process called glycolysis. Glycolysis produces energy and lactate, the latter of which scientists can detect in the blood. 

Professional athletes monitor their lactate levels during performance testing as a way to evaluate their fitness and training program. In addition, doctors measure lactate during exercise testing of patients for conditions marked by abnormally high lactate levels, such as heart or lung disease. Currently, lactate testing is inconvenient and intrusive because blood samples must be collected from the person at different times during the exercise regime and then analyzed. 

Jia therefore have developed a faster, easier and more comfortable way to measure lactate during exercise. They imprinted a flexible lactate sensor onto temporary tattoo paper. The sensor contained an enzyme that strips electrons from lactate, generating a weak electrical current. The researchers applied the tattoo to the upper arms of 10 healthy volunteers. Then the team measured the electrical current produced as the volunteers exercised at increasing resistance levels on a stationary bicycle for 30 minutes. In this way, they could continuously monitor sweat lactate levels over time and with changes in exercise intensity. 

Biobatteries offer certain advantages over conventional batteries: They recharge more quickly, use renewable energy sources (in this case, sweat), and are safer because they do not explode or leak toxic chemicals.