Epidermal Impedance Sensing Sheets for Precision Hydration Assessment and Spatial Mapping

Abstract

This paper presents a class of hydration monitor that uses ultrathin, stretchable sheets with arrays of embedded impedance sensors for precise measurement and spatially multiplexed mapping. The devices contain miniaturized capacitive electrodes arranged in a matrix format, capable of integration with skin in a conformal, intimate manner due to the overall skin-like physical properties. These "epidermal" systems noninvasively quantify regional variations in skin hydration, at uniform or variable skin depths. Experimental results demonstrate that the devices possess excellent uniformity, with favorable precision and accuracy. Theoretical models capture the underlying physics of the measurement and enable quantitative interpretation of the experimental results. These devices are appealing for applications ranging from skin care and dermatology, to cosmetology and health/wellness monitoring, with the additional potential for combined use with other classes of sensors for comprehensive, quantitative physiological assessment via the skin.

Design, Fabrication and Failure Analysis of Stretchable Electrical Routings

“…( b ) Electronic sheets determining the hydration of body. Reproduced with permission from [2]; published by IEEE, 2013. ( c ) Smart contact lens with a function of measuring the glucose level.…”

“…For the human body, a health monitor capable of detecting temperature, activity, and electrocardiography (ECG) signals was developed as an epidermal device which could be hidden and protected by a temporary transfer tattoo [1] (Figure 2a). Similar technology is also applied in an electronic sheet [2] (Figure 2b) which determines the hydration of the body during the training of an athlete and gives periodical reminders to drink for maintaining proper hydration. Different from previous devices in style, a smart contact lens developed with an embedded sensor can measure the glucose levels of diabetics to help their daily health tracking [3] (Figure 2c).…”

Conformability of a Thin Elastic Membrane Laminated on a Soft Substrate With Slightly Wavy Surface

“…In addition to adhesion strength, conformability of thin membranes on rough surfaces also plays a significant role in the functionality of bio-integrated electronics [8], which have sprung up in recent years due to unlimited potentials in disease monitoring, diagnosis, treatment, as well as human-machine interfaces. Intimate contact between device sheet and bio-tissue is required for superior signal-to-noise ratio in both implantable [9,10] and epidermal [11][12][13][14] electrophysiological sensors, hydration sensors [15], and temperature detectors [16]. As another example, wearable heaters for thermoregulation and thermal treatment [17,18] require uniform and efficient heat transfer at the heater-tissue interface, which fully relies on intimate heater-tissue contact.…”

Epidermal mechano-acoustic sensing electronics for cardiovascular diagnostics and human-machine interfaces

“…Many of these operational modes rely critically on an intimate, physical interface to the skin. Examples include precision measurement of temperature and thermal transport characteristics ( 14 , 15 ), recording of electrophysiological processes and variations in electrical impedance ( 16 – 18 ), characterization of skin stiffness ( 5 , 19 ), and monitoring of quasi-static or dynamic dimensional changes, such as those associated with swelling/deswelling or pulsatile blood flow ( 20 , 21 ). The critical enabling properties of the devices and their interfaces with the skin include low thermal and electrical contact resistances, small thermal masses, and soft, compliant mechanics.…”