Researchers at the University of California San Diego have created a temporary tattoo that uses sweat to power your smartphone while you're at the gym.
The device, which was presented at the 248th National Meeting & Exposition of the American Chemical Society (ACS) in San Francisco recently, is also designed to keep track of your progress while you work out, according to Discovery News. Lactate levels, which exist naturally in perspiration, are monitored because of their ability to show how well you're doing in certain exercises.
The tattoo paper is almost as big as a large postage stamp. It comes with a flexible lactate sensor that uses an enzyme to pull electrons from the lactate and generate a small electric current to power the battery.
The initial intention for the device was to use it for diagnostics, according to The Washington Post. High levels of lactic acid in sweat can be caused by certain medical conditions, and in previous tests, doctors had to collect blood samples throughout a person's workout.
The sweatiest test subjects produced 70 microwatts of power per square centimeter of skin, but the small electrodes only managed to store about four microwatts. A basic watch would require 10 microwatts to be fully charged. The researchers actually found that less-fit participants produced more lactic acid than athletic participants, which helped them produce more electrical power.
The team believes the more out-of-shape test subjects produced more sweat because less-fit people get tired earlier while exercising, which jumpstarts glycolysis, a process that produces energy as well as lactic acid, Discovery News reported. The team is looking to use more efficient electronics, as well as larger tattoos, to improve the tattoo's ability to store power.
"The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices," researcher Wenzhao Jia said.
Measuring lactaic acid levels is one of the health benefits of the sensor. Glycolysis is activated when a person goes through intense workouts, and high levels of lactate can indicate that the person will experience heart or lung disease.
The current version of the device only costs a few cents to make and can be used for between 10 and 12 hours, The Washington Post reported.
Despite the improvements needed for the tattoo, the team believes a future where biobatteries are used to power different kinds of smart devices is not far away.
