Wearable sensors that track steps or heart
rates are popular fitness products. But in the future, working up a good sweat
could provide useful information about your health. Now, researchers reporting in ACS Applied
Materials & Interfaces have developed a headband that measures electrolyte levels in sweat. The headband could let users know when it’s
time to replenish these essential ions that are lost when sweating. And unlike many previous sweat sensors, this
device can heal itself when cut or scratched during exercise. Human sweat contains substances, such as metabolites,
electrolytes and heavy metals, that can indicate a person’s health and even help diagnose
some diseases. In recent years, scientists have developed
patches, bandages and tattoos that can analyze sweat, but movements like walking, running,
jumping or throwing can affect their performance. Also, if the sensors become scratched or broken,
which can easily happen during exercise, they often can’t be repaired. Sung Yeon Hwang, Jeyoung Park, Bong Gill Choi
and colleagues wanted to develop a sweat sensor that could withstand the wear and tear of
exercise, and quickly repair itself if damaged. First, the researchers developed a self-healing
polymer based on citric acid, a natural compound found in citrus fruits. When they cut a piece of the polymer with
a razor blade, and then pressed the cut ends together, the polymer healed itself through
hydrogen bonding. The healed polymer was strong enough to lift
a 2-pound weight without breaking. Then, the researchers coated carbon fiber
threads with the self-healing polymer. The threads were electrodes that could detect
potassium and sodium ions in sweat. The team added a wireless electronic circuit
board that transfers data to a smart phone. When the researchers added a solution containing
potassium to the threads, they detected the ions and transmitted the signal to a smart
phone. The threads could be cut and then reattached,
restoring the ion signal. To find out if the sweat sensor actually works
during exercise, the researchers sewed the threads and circuit board into a headband. A human volunteer wore the headband while
exercising on a stationary bike, and the sensor accurately tracked the sodium and potassium
electrolytes in his sweat over 50 minutes of exercise. The researchers could even cut the sensor
threads with scissors during cycling, and the threads healed and returned to normal
operation in only 20 seconds. The researchers say the sweat-sensing threads
could be sewed into any knitted garments, including T-shirts, wristbands, socks, and