Wearable Interdigitated Capacitive Sensor with Flexible Analog Front End for Superficial Skin Hydration Measurements

Wearable sensors and e-textiles have had an impact on many fields of healthcare, including dermatology. Superficial skin hydration is a biomarker for conditions like atopic dermatitis (AD), yet most hydration sensors are not optimised for measurement in the outermost layer of the skin - the stratum corneum (SC). In this paper, the authors present an interdigitated capacitor (IDC), tailored specifically for monitoring the shallow SC layer. The sensor is printed onto a wearable textile strap and is complemented by a custom flexible analog front end (AFE) to allow for continuous monitoring of the SC. The IDC is tested on volunteers, and the results reveal a 7% change in capacitance between skin with dry SC layer and skin with hydrated SC layer. The sensor can also be used to monitor treatments and shows that a particular commercial cream's effect wears off after 2.5 hours. The e-textile IDC can also survive a standard ISO wash test with limited electrical defects.