Our skin helps protect us from the elements, regulates body temperature, and allows us to feel sensations like touch and temperature. Our skin can also provide information to others. If we have a fever, our forehead is warm; if we are embarrassed, our skin might turn red; and if we are exercising or stressed, we sweat.
Wei Gao, assistant professor in the Andrew and Peggy Cherng Department of Medical Engineering at Caltech, wants to learn even more about the skin and has developed an electronic skin (e-skin) that can be worn over the skin and is embedded with sensors that can monitor vital functions, blood sugar, and other metabolic byproducts. This electric skin runs on biofuel cells powered by one of the body’s waste products, so it does not require batteries.
"One of the major challenges with these kinds of wearable devices is on the power side," says Gao. "Many people are using batteries, but that's not very sustainable. Some people have tried using solar cells or harvesting the power of human motion, but we wanted to know, 'Can we get sufficient energy from sweat to power the wearables?' and the answer is yes."
Human sweat contains high concentrations of lactate, which is generated when we exercise our muscles. The fuel cells that are in the e-skin absorb lactate and combine it with oxygen. The e-cells generate enough electricity to transmit readings wirelessly.
"While near-field communication is a common approach for many battery-free e-skin systems, it could be only used for power transfer and data readout over a very short distance," Gao says. "Bluetooth communication consumes higher power but is a more attractive approach with extended connectivity for practical medical and robotic applications."
Gao wants to develop an array of sensors for the e-skin so that it can be used for various applications. Gao explains, "We want this system to be a platform. In addition to being a wearable biosensor, this can be a human-machine interface. The vital signs and molecular information collected using this platform could be used to design and optimize next-generation prosthetics." Gao's research is published in the journal, Science Robotics.