Efficient Skin Temperature Sensor and Stable Gel‐Less Sticky ECG Sensor for a Wearable Flexible Healthcare Patch

Abstract

Because a wearable device comprised of a flexible film should be comfortable to wear over the skin, several reports have focused on the film thickness to prepare ultrathin films that are a few micrometers or nanometers thick. [26,27] Thinning a film to this scale should realize a film capable of covering the skin asperity conformally, resulting in a good comfort while wearing and a relatively strong adhesion on skin without glue. However, ultrathin films can be difficult to handle and attach to skin. Additionally, assembling other components such as a signal processing circuit and battery without sacrificing the advantage of thickness remains challenging. Thus, many reports still employ both ultrathin film flexible devices and relatively thick films (several hundred micrometers). [1,[4][5][6][7]9,12,16,18,19,22,28] However, the effect of film thickness on sensing has yet to be discussed, although a systematical study is important to realize precise health data recordings. In addition to the wearability and film thickness depedences, biocompatibility of the sensor and film materials is another important parameter to consider for the practical application as a wearable device.In this study, we explore the dependence of the temperature change, which is measured by a printed temperature sensor fabricated on polyethylene terephthalate (PET), on thickness. A thick film was selected due to handling ease and ability to integrate other components in the future. However, some sensors such as an ECG sensor must attach onto skin with good adhesion without sacrificing conductivity, and a relatively thick flexible film itself cannot attach to skin without an adhesion layer. To create good adhesion between an ECG sensor and skin without losing conductivity, a high adhesive conductive polymer onto skin is also developed. Although gel-based electrodes are often used in medical applications, gel-based electrodes are unsuited for long-time measurements due to skin irritation. [15] Thus, we developed a gel-less sticky electrode using biocompatible materials by characterizing the adhesion, impedance between skin and the ECG sensor, and repeatability for use. Finally, as a proofof-concept demonstration, simultaneous efficient skin temperature and ECG signal recordings were conducted using a conductive polymer with an optimized film thickness. Figure 1a describes an integrated device image with a temperature sensor, an ECG sensor, an equivalent circuit between Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail. In this study, the effect of film thickness for skin te...

Multifunctional Skin‐Inspired Flexible Sensor Systems for Wearable Electronics

“…Results of the real‐time ECG signal and skin temperature monitoring with a control temperature measurement using an IR sensor at e) standing up and sitting down states and f) strong‐step states. c–f) Reproduced with permission . Copyright 2017, John Wiley & Sons.…”

“…In addition, a good adhesion is often pivotal between some flexible sensors and skin, so that an adhesion layer is mostly applied despite its unsuitability for long‐time measurements owing to skin irritation. Recently, a multifunctional flexible healthcare patch is developed by integrating an efficient skin temperature sensor and a gel‐less sticky ECG sensor (Figure c,d) . It is found the film thickness should be thinner to accurately measure the skin temperature and the optimization of material concentration of CNT, PEIE, as well as PDMS could yield a relatively reliable gel‐less ECG sensor.…”

Physical sensors for skin‐inspired electronics

“…Various flexible and conformable electrophysiological sensors have been developed for long‐term monitoring electrophysiological signals. ECG is the best way to measure heart rhythms and has been widely used for diagnosing heart disease . EMG can record the electrical activity produced by skeletal muscles, which can be used to diagnose neuromuscular diseases and control prosthetic devices .…”

Textile‐Based Flexible Tactile Force Sensor Sheet

“…Printing or similar fabrication processes can contribute to the scalability and affordability for multifunctional flexible electronics. In fact, many macroscale printing sensing sheets have been proposed, suggesting that a variety of methods show potential for the concept . In particular, textile‐based flexible sensors have been reported previously to demonstrate macroscale and different functionalities such as strain detection .…”