A group of scientists at the University of California San Diego have come up with a novel way to power wearable Health Tech devices: sweat. When you exercise your muscles, they produce lactate. The harder your muscles work, the more lactate they produce. Athletes and trainers monitor lactate production as a way to evaluate how strenuous a workout session is, and healthcare professionals track lactate levels for patients with heart or lung disease, or other conditions. The UCSD researchers were investigating ways to monitor lactate levels in real time. Their solution was to use an enzyme that can strip electrons from the compound, which produces a weak electrical current.
They then came up with a clever way to apply this enzyme. They printed a temporary tattoo on special transfer paper, using different inks in layers to create electrodes and insulators. The final layer is an adhesive that is porous to allow the sweat from the skin to reach the electrodes.
By measuring the current produced by these tattoos, it is possible to track the amount of lactate in the sweat. This eliminates the need to draw blood to get a reading. The researchers see applications beyond just monitoring lactate levels, however. If the tattoos can be made to produce electrical power more efficiently, they could become a practical means of powering sensors on human subjects during exercise for training or medical purposes. They could lead to printable, disposable wireless sensors that would be inexpensive and effective.