Article Cite This: Acc. Chem. Res. 2019, 52, 91−99
pubs.acs.org/accounts
Stretchable, Skin-Attachable Electronics with Integrated Energy Storage Devices for Biosignal Monitoring Published as part of the Accounts of Chemical Research special issue “Wearable Bioelectronics: Chemistry, Materials, Devices, and Systems”. Yu Ra Jeong,†,§ Geumbee Lee,‡,§ Heun Park,†,§ and Jeong Sook Ha*,†,‡
Downloaded via IOWA STATE UNIV on January 16, 2019 at 10:58:08 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
†
Department of Chemical and Biological Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea ‡ KU-KIST Graduate School of Converging Science and Technology, 145, Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea CONSPECTUS: The demand for novel electronics that can monitor human health, for example, the physical conditions of individuals, during daily life using different techniques from those used in traditional clinic diagnostic facilities is increasing. These novel electronics include stretchable sensor devices that allow various biosignals to be directly measured on human skin without restricting routine activity. The thin, skin-like characteristics of these devices enable stable operation under various deformations, such as stretching, pressing, and rubbing, experienced while attached to skin. The mechanically engineered design of these devices also minimizes the inconvenience caused by long-term wear owing to conformal lamination on the skin. The final form of a skin-attachable device must be an integrated platform with an independent and complete system containing all components on a single, thin, lightweight, stretchable substrate. To fabricate fully integrated devices, various aspects, such as material design for deformable interconnection, fabrication of high-performance active devices, miniaturization, and dense arrangement of component devices, should be considered. In particular, a power supply system is critical and must be combined in an electromechanically stable and efficient manner with all devices, including sensors. Additionally, the biosignals obtained by these sensors should be wirelessly transmitted to external electronic devices for free daily activity. This Account covers recent progress in developing fully integrated, stretchable, skin-attachable devices by presenting our strategies to achieve this goal. First, we introduce several integration methods used in this field to build stretchable systems with a special focus on the utilization of liquid gallium alloy. The unique characteristics and patterning process of liquid metal are summarized. Second, various skin-attachable sensors, including strain, pressure, with enhanced sensitivity and mechanical properties are discussed along with their applications for biosignal monitoring. Dual mode sensors that simultaneously detect temperature and pressure signals without interference are also introduced. Third, we emphasize supercapacitors as promising, efficient energy storage devices for power management systems in wearable devices. Supercapacitors for skin-attachable applications should have a high performance, such as high operation voltage, high energy and power densities, cyclic and air stability and water resistance. For this, strategies to select novel materials for electrode, electrolyte, and encapsulation are suggested. Several approaches to fabricate stretchable supercapacitor systems are also presented. Finally, we introduce recent examples of skin-attachable, stretchable electronics that integrate sensors, power management devices, and wireless data transfer functions on a single elastomer substrate. Conventional wireless technologies, such as near-field communications (NFC) and Bluetooth, are incorporated in miniaturized features on the devices. To date, much research has been performed in this field, but there are still many technologies to develop. The performance of individual devices and mass fabrication techniques should be enhanced. We expect that future electronic devices with fully integrated functions will include advanced human−machine interaction capabilities and expand the overall abilities of the human body.
1. INTRODUCTION: STRETCHABLE ELECTRONICS FOR SKIN-ATTACHABLE APPLICATIONS
addition to precisely measuring signals from the human body during dynamic movements. One of the best strategies for this purpose is to create skin-attachable devices that can conformally
The goal of wearable electronics is to acquire real-time, useful information related to health conditions and human activities. The materials and hardware design should consider the comfort of individuals who wear the devices during everyday activities in © 2018 American Chemical Society
Received: October 5, 2018 Published: December 26, 2018 91
DOI: 10.1021/acs.accounts.8b00508 Acc. Chem. Res. 2019, 52, 91−99
Article
Accounts of Chemical Research
Figure 1. A schematic illustration of a fully integrated, stretchable, skin-attachable device.
Figure 2. Examples of stretchable interconnections for integrated skin-attachable electronics. (a) Optical and finite element analysis (FEA) modeling images of serpentine (top) and fractal (bottom) structures before and after stretching. Reproduced with permission from refs 1 and 2. Copyright 2008 National Academy of Sciences U.S.A. and 2014 Nature Publishing Group. (b) An elastic conductor based on in situ formation of silver nanoparticles from silver flakes in fluorine rubber. Reproduced with permission from ref 3. Copyright 2017 Nature Publishing Group. (c) (i) Optical microscopy and (ii) FEA images of a 5 × 5 array of rigid PET islands connected with liquid metal interconnections under biaxial stretching. Reproduced with permission from ref 4. Copyright 2017 Nature Publishing Group.
at levels comparable to those of rigid devices. Most studies have focused on developing individual skin-attachable devices. However, it is of crucial importance to create a skin-attachable, stretchable system that integrates all components onto a single deformable elastomer substrate. Figure 1 shows a schematic illustration of a stretchable, skin-attachable device with integrated key functions. In a fully integrated device, the sensors that monitor biosignals, the supercapacitors that power the active sensor devices, and a wireless system that interacts with external facilities are connected via stretchable interconnections. In this Account, we present research progress on current skinattachable electronics, that is, from individual components to a
attach to skin. To enable conformal lamination of the devices on skin, either the thickness of the flexible substrate should be extremely thin (
