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Sensor Patch Captures Health Indicators in Sweat

Runner silhouettes

(Skeeze, Pixabay)

29 July 2020. A bio-engineering lab created a wearable fabric patch with threads configured into sensors that capture and measure health indicators from human sweat. A team from the Nano Lab at Tufts University in Medford, Massachusetts headed by engineering professor Sameer Sonkusale, describes the device and test results in yesterday’s issue of the journal NPJ Flexible Electronics.

Perspiration offers an easily accessible source of health information, particularly for indicators of water intake and metabolic functions. These data are often not collected in most wearable health monitors that measure heart and respiratory activity. For example, sweat can be analyzed for sodium content that offers indicators of hydration and electrolyte balance, lactate concentration as a measure of muscle fatigue, the hormone cortisol for measuring emotional stress, glucose for monitoring energy level or diabetes, and ammonium as a metabolic indicator of liver functioning. Athletes, who today often monitor multiple physiological measures, would be prime candidates for this technology.

Sonkusale’s lab at Tufts studies flexible bio-electronics, particularly for sensors and smart bandages. (Science & Enterprise reported on one of the lab’s smart bandages in July 2018.) Textiles offer a useful platform for sensors measuring sweat, say the authors, since textile threads are abundant, inexpensive, renewable, and biodegradable. The challenge in using textile threads for medical sensors is integrating electronics, which are rigid and uncomfortable if worn directly on skin.

The team led by then-postdoctoral researcher and first author Trupti Terse-Thakoor uses commercial polyester threads coated with conductive carbon inks that, in effect, turn the threads into electrodes. The threads are then deposited with one of a series of sensing chemicals or enzymes for measuring acidity with pH, electrolytes with ammonium and sodium, metabolites with lactates, and threads coated with polyvinyl butyral for reference measurements.

Researchers fabricated the threads into small, wearable patches about the size of a band-aid dressing, covered with gauze to wick sweat from the wearers, and sewn into cloth bands worn on the upper arm, waist, or forehead for testing. The devices transmit their data wirelessly to nearby commercial monitors. The seven individuals testing the sensor patches included trained athletes and people in normal physical condition, who rode stationary exercise bicycles for 30 minutes at a time to reach maximum exertion.

The proof-of-concept results show sodium, ammonium, and lactate readings from the sweat sensors vary consistently as the exercise continues. However, the study did not correlate the findings with performance or conditioning.

“The sensor patch that we developed is part of a larger strategy to make completely flexible thread-based electronic devices,” says Sonkusale in a university statement released through EurekAlert. “Flexible devices woven into fabric and acting directly on the skin means that we can track health and performance not only non-invasively, but completely unobtrusively. The wearer may not even feel it or notice it.”

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