Wearable or attachable health monitoring smart systems are considered to be the next generation of personal portable devices for remote medicine practices. Smart flexible sensing electronics are components crucial in endowing health monitoring systems with the capability of real-time tracking of physiological signals. These signals are closely associated with body conditions, such as heart rate, wrist pulse, body temperature, blood/intraocular pressure and blood/sweat bio-information. Monitoring such physiological signals provides a convenient and non-invasive way for disease diagnoses and health assessments. This Review summarizes the recent progress of flexible sensing electronics for their use in wearable/attachable health monitoring systems. Meanwhile, we present an overview of different materials and configurations for flexible sensors, including piezo-resistive, piezo-electrical, capacitive, and field effect transistor based devices, and analyze the working principles in monitoring physiological signals. In addition, the future perspectives of wearable healthcare systems and the technical demands on their commercialization are briefly discussed.

Flexible Sensing Electronics for Wearable/Attachable Health Monitoring

Exciting advancements have been made in the field of flexible electronic devices in the last two decades and will certainly lead to a revolution in peoples’ lives in the future. However, because of the poor sustainability of the active materials in complex stress environments, new requirements have been adopted for the construction of flexible devices. Thus, hierarchical architectures in natural materials, which have developed various environment-adapted structures and materials through natural selection, can serve as guides to solve the limitations of materials and engineering techniques. This review covers the smart designs of structural materials inspired by natural materials and their utility in the construction of flexible devices. First, we summarize structural materials that accommodate mechanical deformations, which is the fundamental requirement for flexible devices to work properly in complex environments. Second, we discuss the functionalities of flexible devices induced by nature-inspired stru...

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Nature-Inspired Structural Materials for Flexible Electronic Devices

Stretchable and flexible sensors attached onto the surface of the human body can perceive external stimuli, thus attracting extensive attention due to their lightweight, low modulus, low cost, high flexibility, and stretchability. Recently, a myriad of efforts have been devoted to improving the performance and functionality of wearable sensors. Herein, this review focuses on recent remarkable advancements in the development of flexible and stretchable sensors. Multifunction of these wearable sensors is realized by incorporating some desired features (e.g., self-healing, self-powering, linearity, and printing). Next, focusing on the characteristics of carbon nanomaterials, nanostructured metal, conductive polymer, or their hybrid composites, two major strategies (e.g., materials that stretch and structures that stretch) and diverse design approaches have been developed to achieve highly flexible and stretchable electrodes. Strain sensing performances of recently reported sensors indicate that the appropria...

Recent Advancements in Flexible and Stretchable Electrodes for Electromechanical Sensors: Strategies, Materials, and Features

Conductive hydrogels are promising materials for soft electronic devices. To satisfy the diverse requirement of bioelectronic devices, especially those for human–machine interfaces, hydrogels are required to be transparent, conductive, highly stretchable, and skin-adhesive. However, fabrication of a conductive-polymer-incorporated hydrogel with high performance is a challenge because of the hydrophobic nature of conductive polymers making processing difficult. Here, we report a transparent, conductive, stretchable, and self-adhesive hydrogel by in situ formation of polydopamine (PDA)-doped polypyrrole (PPy) nanofibrils in the polymer network. The in situ formed nanofibrils with good hydrophilicity were well-integrated with the hydrophilic polymer phase and interwoven into a nanomesh, which created a complete conductive path and allowed visible light to pass through for transparency. Catechol groups from the PDA–PPy nanofibrils imparted the hydrogel with self-adhesiveness. Reinforcement by the nanofibrils ...

Transparent, Adhesive, and Conductive Hydrogel for Soft Bioelectronics Based on Light-Transmitting Polydopamine-Doped Polypyrrole Nanofibrils

A transparent, conductive, and flexible electrode is demonstrated. It is based on an inexpensive and easily manufacturable metallic network formed by depositing metals onto a template film. This electrode shows excellent electro-optical properties, with the figure of merit ranging from 300 to 700, and transmittance from 82% (~4.3 Ω sq(-1) ) to 45% (~0.5 Ω sq(-1) ).

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Uniform Self-Forming Metallic Network as a High-Performance Transparent Conductive Electrode

Biological systems, subject to evolutionary optimization over millions of years, have been a source of ingenious solutions in many areas of science. Here, Han et al. develop transparent electrodes inspired by two such systems: a leaf venation and a spider’s web.

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Bio-inspired networks for optoelectronic applications

Conjugated polymers with donor–acceptor architectures have been successfully applied in bulk heterojunction solar cell devices. Tuning the electron-withdrawing capability in donor–acceptor (D–A) conjugated polymers allows for design of new polymers with enhanced electrical and optical properties. In this paper, a series of D–A copolymers, PBDFDTBT (P1a), PBDTDTBT (P2a), PNDTDTBT (P3a), and PQDTDTBT (P4a), were selected and theoretically investigated using PBE0/6-311G** and TD-PBE0/6-311G**//PBE0/6-311G** methods. The calculated results agree well with the available experimental data of HOMO energy levels and band gaps. We further designed and studied four novel copolymers, P1b, P2b, P3b, and P4b, by substituting the 2,1,3-benzothiadiazole (BT) unit in P1a–P4a with a stronger unit of naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole (NT), respectively. Compared with P1a–P4a, the newly designed polymers of P1b–P4b show better performance with the smaller band gaps and lower HOMO energy levels. The PCEs of ∼5%, ∼7%,...

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Theoretical Investigations on Donor–Acceptor Conjugated Copolymers Based on Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole for Organic Solar Cell Applications

https://statics.scnu.edu.cn/pics/aoe/2014/0926/20140926041406753.pdf

Rational design of novel A-A-D-A-A type electron donors for small molecule organic solar cells

This work presents an inexpensive and easily manufacturable, highly conductive and transparent nanowire network electrode for textured semiconductors. It is based on lines of silver nanoparticles transformed into a nanowire network by microwave or furnace sintering. The nanonetwork electrode on crystalline silicon is demonstrated experimentally, with the nanoparticles self-assembling in the valleys between the pyramids of the textured surface. Optical experiments show that this conductive nanowire network electrode can be essentially 'invisible' when covered with the conventional anti-reflection coating (ARC), and thus could be employed in photovoltaic applications.

https://statics.scnu.edu.cn/pics/aoe/2014/0926/20140926032406760.pdf

Ke Pei

Papers

Uniform Self-Forming Metallic Network as a High-Performance Transparent Conductive Electrode

Bio-inspired networks for optoelectronic applications

Theoretical Investigations on Donor–Acceptor Conjugated Copolymers Based on Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole for Organic Solar Cell Applications

Rational design of novel A-A-D-A-A type electron donors for small molecule organic solar cells

Transparent Nanowire Network Electrode for Textured Semiconductors