Researchers have developed the first thread-based flexible patch that can be sewn into clothing to monitor — in real time — several molecules in sweat, including chloride ions, which are dysregulated in cystic fibrosis (CF) patients.
The study describing that finding, “Thread-based multiplexed sensor patch for real-time sweat monitoring,” was published recently in the journal Nature NPJ Flexible Electronics.
The new device consists of unique sensing threads, electronic components, and wireless connectivity to acquire, store, and process data.
While the work is still in its early stages, it opens the door to cost-effective, unnoticeable, wearable sensors that can be used to assess athletic fitness or diagnose and monitor chronic and acute health conditions, such as CF.
“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,” Sameer Sonkusale, PhD, said in a press release. Sonkusale is the study’s senior author and professor of electrical and computer engineering at Tufts University School of Engineering in Massachusetts.
Over the years, several wearable electronic devices, including small patches and wristbands, have been developed to monitor relevant health biomarkers in sweat, including chloride ions, sodium, glucose (sugar), and lactate — a product of glucose metabolism and energy production.
“Sweat is a useful fluid for health monitoring since it is easily accessible and can be collected non-invasively,” said Trupti Terse-Thakoor, PhD, the study’s first author and a former post-doctoral scholar at Tufts.
“The markers we can pick up in sweat also correlate well with blood plasma levels which makes it an excellent surrogate diagnostic fluid,” Terse-Thakoor added.
Of note, the levels of chloride ions can be used to diagnose and monitor CF, sodium levels can indicate the body’s hydration status and electrolyte imbalance, glucose levels allow to assess a person’s energy level and monitor diabetes, and lactate levels can serve as an indicator of muscle fatigue.
Other markers in sweat include: cortisol, a stress hormone, for assessing emotional stress as well as metabolic and immune functions; and ammonium as a marker for metabolic conditions related to protein breakdown as a result of diet, liver dysfunction, or low oxygen levels.
Collaborative work between researchers at Tufts, the Center for Applied Brain and Cognitive Sciences in Massachusetts, and the Indian Institute of Technology Bombay in India, resulted in the development of the first thread-based wearable sweat sensor that can be integrated easily into clothing.
The new device was designed to allow real-time measurement of health biomarkers, including electrolytes (sodium and ammonium), metabolites (lactate), and pH levels in a person’s sweat.
The sensors are made from conductive thread, coated so as to respond to the particular biomarker being assessed. By changing the threads’ coating, the device may potentially track nearly every relevant biomarker in sweat.
The array of thread sensors can be integrated into a patch or clothing, and connected to a miniature circuit and microprocessor, which can communicate with a smartphone through a wireless connection.
The sweat sensor platform was built as a patch on which threads are placed directly on the fabric gauze of a commercial bandage.
“The fabric gauze facilitates sweat transport from the sensing area or inner side of the patch to the backside of the patch to evaporate,” the researchers wrote. “Continuous sweat evaporation from the gauze ensures that fresh sweat is continually wicked at the sensor surface for real-time measurement.”
Detailed sensor patch analyses showed that it could be used for a minimum of three hours without significant changes in sensor response.
Researchers then tested the device in seven volunteers, including men and women with different fitness levels and diets. The sensor patch was applied to their skin in the lower back, forehead, or the arms before they underwent a minimum of 30 minutes exercise either on a stationary bike or on a treadmill.
Sweat samples were collected from the volunteers during the tests to compare with data collected with the sensor patch.
Results showed that the sensors effectively detected variations in biomarker levels within intervals of five to 30 seconds — consistent with commercially available real-time tracking technologies.
While the study was not intended to establish an association between the levels of the selected biomarkers and performance or conditioning, the researchers believe it certainly established that the sensor could detect consistent patterns of biomarkers levels. These patterns may be used in future studies to identify such associations.
“Beyond a patch, one can realize sweat sensing platform by stitching/sewing thread-based electrodes directly into any clothing (e.g., shirts and hats),” the team wrote, noting that this opens “avenues for cost-effective, flexible wearable [multiple] monitoring of athletic fitness or health management.”
“The sensor patch that we developed is part of a larger strategy to make completely flexible thread-based electronic devices,” Sonkusale said.
The team noted that further work is still needed to extensively validate the new device and to improve sensor design to make it even more flexible and more accurate.
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