Last year, researchers at the University of California, San Diego (UCSD) unveiled a sensor imprinted on a temporary tattoo that, when applied to the skin, is able to continuously monitor lactate levels in a person's sweat as they exercise. Now the research team has leveraged the technology to create a biobattery powered by perspiration that could lead to small electronic devices being powered by sweat.

As reported last year, a UCSD research team developed a sensor that is able to accurately monitor lactate levels, allowing athletes to ease up on their workout before fatigue sets in. They did this by taking a flexible sensor containing an enzyme that strips electrons from lactate to generate a weak electrical current, and imprinting it onto temporary tattoo paper.

The team applied the tattoo to the upper arms of 10 healthy volunteers and measured the electrical current produced as they exercised at increasing levels of resistance on a stationary bicycle for 30 minutes. By measuring the changes in the electrical current, the researchers were able to continuously monitor sweat lactate levels over time and with changes in exercise intensity.

Taking the technology a step further, the researchers have now created a biobattery powered by sweat. Also taking the form of a temporary tattoo, the biobattery features an anode containing the same enzyme used in the sensor that removes electrons from lactate, and a cathode containing a molecule that accepts the electrons.

To test the biobattery, the researchers applied the temporary tattoos to the upper arms of 15 volunteers who again worked up a sweat on a stationary bike. The researchers found that different people produced different amounts of power, with people who were less fit producing more power than those who were moderately fit, while the fittest produced the least power of all. The researchers attributed this to the fact that people who are less fit become fatigued sooner, resulting in more lactate being produced sooner. A person in the low fitness group, which exercised less than once a week, produced the greatest amount of energy at 70 microWatts per cm2 of skin.

"The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices," says Wenzhao Jia, a postdoctoral student in the lab of Joseph Wang, D.Sc., at UCSD. "Right now, we can get a maximum of 70 microWatts per cm2, but our electrodes are only 2 by 3 mm 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."

The team points out that biobatteries hold a number of advantages over conventional batteries, in that they recharge faster, make use of renewable energy sources (in this case, sweat) and don't explode or leak toxic chemicals.

The researchers presented their biobattery at the 248th National Meeting & Exposition of the American Chemical Society (ACS) being held this week in San Francisco.

The video below describes the technology and its potential applications.