Skin-Inspired Healthcare Electronics

Abstract

With the improvement in living standards and the aging of the population, the development of thin, light, and unobtrusive electronic skin devices is accelerating. These electronic devices combine the convenience of wearable electronics with the comfort of a skin-like fit. They are used to acquire multimodal physiological signal data from the wearer and real-time transmission of signals for vital signs monitoring, health dynamics warning, and disease prevention. These capabilities impose unique requirements on material selection, signal transmission, and data processing for such electronic devices. Firstly, this review provides a systematic introduction to nanomaterials, conductive hydrogels, and liquid metals, which are currently used in human health monitoring. Then, it introduces the solution to the contradiction between wireless data transmission and flexible electronic skin devices. Then, the latest data processing progress is briefly described. Finally, the latest research advances in electronic skin devices based on medical scenarios are presented, and their current development, challenges faced, and future opportunities in the field of vital signs monitoring are discussed.

Keywords: electronic skin; flexibility; health monitoring; vital signs monitoring; wearable devices.

Figure 1

Skin-inspired healthcare electronics in terms of material selection, signal transmission, and application. Body temperature sensor. Reprinted with permission from Ref. [24] (copyright 2024 Wiley-VCH GmbH). Pulse sensor. Reprinted with permission from Ref. [32] (copyright 2023 Wiley-VCH GmbH). Blood pressure sensor. Reprinted with permission from Ref. [33] (copyright 2023 Jian Li et al.). Blood oxygen sensors. Reprinted with permission from Ref. [23] (copyright 2022 Lijia Pan, Yi Shi, Xinran Wang et al.).

Figure 2

Material selection for novel skin electronics. (a) Microcracked flexible pressure sensor prepared using 1D nanomaterial silver nanowires. Reprinted with permission from Ref. [60] (copyright 2021 Wiley-VCH GmbH). (b) Two-dimensional nanomaterial porous graphene. Reprinted with permission from Ref. [69] (copyright 2021 Wiley-VCH GmbH). (c) Highly mechanically stable conductive hydrogel based on PAM, lithium chloride, and PEDOT–PSS covered by nanofibers. Reprinted with permission from Ref. [111] (copyright 2022 Wiley Periodicals LLC). (d) Liquid metal columnar electrodes made by 3D printing technology. Reprinted with permission from Ref. [108] (copyright 2024 Sanghoon Lee, Won Gi Chung, Han Jeong et al.).

Figure 3

Temperature sensors. (a) Wearable ionic temperature sensor arrays with hydrogels that can detect temperature distribution at the wrist. Reprinted with permission from Ref. [24] (copyright 2024 Wiley-VCH GmbH). (b) Skin-inspired soft robots that can be wirelessly controlled to enter the human body to measure temperature, etc. Reprinted with permission from Ref. [154] (copyright 2024 Lin Zhang et al.).

Figure 4

Mechanism of PPG signal, signal curve composition, and application scenarios. Reprinted with permission from Ref. [32] (copyright 2023 Wiley-VCH GmbH). (a) Diagram of the human blood circulation system and schematic diagram of PPG signal sensing on the body surface. (b) Structure of the basic curve of the PPG signal and the structure of the response of different parts of subcutaneous tissue.

Figure 5

Wearable pulse pressure sensors. (a) Schematic diagram of wearable pulse sensor structure. Reprinted with permission from Ref. [160] (copyright 2022 Wiley-VCH GmbH). (b) Schematic illustration of the (I) fabrication, (II) structure, and (III) application of EMPAs. Reprinted with permission from Ref. [161] (copyright 2022 Jia-Han Zhang et al.).

Figure 6

Blood pressure and oxygen sensors. (a) Wearable continuous blood pressure monitoring system based on intraocular pressure measurement. Reprinted with permission from Ref. [33] (copyright 2023 Jian Li et al.). (b) On-skin optoelectronic biosensor that measures tissue oxygen saturation. Expected to be attached to the red circle in the figure for (I) clinical diagnosis, (II) surgical monitoring and (III) postoperative care. Reprinted with permission from Ref. [23] (copyright 2022 Lijia Pan, Yi Shi, Xinran Wang et al.).