A new review highlights the recent advances in making thin, wearable electronics that can measure your physical activities in real-time.
Recent advances in stretchable materials, mechanics, and micro-sensing systems present a new frontier in the development of real-time body measurement. Researchers have come up with an idea to continuously monitor physiological signals and biological fluids, such as human sweat, with a flexible wearable device that easily adheres to the skin. Wearable electronics may be of great importance in healthcare, physiology research, fitness, and athletic performance. A recent review by Rogers and colleagues, published in Science Advances, summarizes the different mechanisms and research prototypes that can be used to measure local sweat loss, as well as several metabolites and analytes.
Sweat Collection and Analysis
Human sweat forms in response to heat, exercise, and body condition. There are a few million sweat glands all over our skin, producing and secreting substances onto our skin surface by way of a sweat duct. Sweat plays a role in nonverbal human communication. It contains physiologically rich information about what is happening in the body with many different electrolyte ions, solutes, and metabolites. This makes it an attractive body fluid for various applications in ambulatory health diagnostic, sports performance, and healthcare monitoring. For example, a sweat chloride test can be used for diagnosing cystic fibrosis in newborns, a noninvasive measure of blood glucose through the analysis of sweat is a viable method for screening diabetes, and a uric acid sweat test can be used for monitoring chronic kidney disease. Besides the sweat chemistry and constitution, localized sweat rate is an important indicator of hyperhidrosis and hypohidrosis for the evaluation of regulation disorder and stroke.
Wearable Electronics for Sweat Analysis
By putting electrochemical sensors in wearable technology, scientists were able to adhere thin hydrogels on flexible printed circuit boards for the continuous monitoring of sweat analytes that emerge from skin pores. For example, enzyme biosensors are designed to measure glucose, lactate, and alcohol, ion-selective electrodes for detecting various electrolytes such as sodium, potassium, and calcium ions. Electrochemical biosensors can be used for sensing heavy metals such as zinc-, lead, and mercury-ions.
Despite the good biocompatibility of porous chitosan, nafion, or polyvinyl chloride loaded hydrogels, these materials cannot capture any sweat to measure sweat rate. Scientists are thinking about building a thin, soft, robust, hydrophilic lab-on-skin microfluidic platform to capture, route, and store microliter quantities of sweat. This body-driven idea relies on pumping and capillary action to move sweat into micro-channelled sensors for real-time onboard analysis without the need for external batteries.
In the future, wearable electronics healthcare application will likely change into soft, skin-like devices, microfluidics, and multifunctional biosensors with capabilities in the real-time monitoring of biophysical activities. Continued technologic advancements in wearable electronics could bring us closer to a powerful, smaller, and less expensive real-time monitoring device over the next several years.
Written by Man-tik Choy, Ph.D
Reference: Choi, J.G. et al. 2018. Skin-interfaced systems for sweat collection and analytics. Science Advances, 4(2), eaar3921. DOI: 10.1126/sciadv.aar3921