Flexible electronic devices to obtain accurate and efficient information interactions between humans and machines have gained increasing attention in recent years. A series of soft materials for flexible electronics have been developed to improve device performance in terms of electrical and mechanical properties. Among them, conductive polymer-based hydrogels (CPHs), which combine the tunable electronic properties of conductive polymers and the soft mechanical properties of hydrogels, are promising candidates for nextgeneration wearable electronic devices. This review summarized the material design and preparation of CPHs, and presented the properties of CPHs, including tunable conductivity, outstanding mechanical performance, biocompatibility, self-healing capability, resistance to freezing, and solution processability.In particular, their emerging applications in flexible electronics devices including flexible supercapacitors, flexible sensors, and biomedical electronics are highlighted. Furthermore, perspectives on existing challenges and opportunities in this field are discussed.
Nanogenerators have received much attention due to their potential applications in mechanical energy harvesting and self-powered sensing. Despite the fast development of nanogenerators, improving their performances via effective strategies still remains a great challenge. Herein, we report a ternary coupling effect of a triboelectric–piezoelectric hybrid nanogenerator based on the nanoporous film of poly(vinylidene fluoride)/BaTiO3 composite nanofibers prepared by electrospinning. The transfer charge density of the triboelectric–piezoelectric hybrid nanogenerator in the optimal coupling state is 2.12 times that of the sum value of the pristine nanoporous piezoelectric and triboelectric nanogenerators as references, which can reach up to 105.6 μC m–2. Enhanced performances of the hybrid nanogenerator are attributed to the improved synergistic coupling for triple effects of pore dipole, triboelectricity, and piezoelectricity. Furthermore, the wearable hybrid nanogenerator is demonstrated to be able to harvest biomechanical energy from actions in life. Our findings provide an effective method for developing high-performance nanogenerators.
It is still a challenge for flexible electronic materials to realize integrated strain sensors with a large linear working range, high sensitivity, good response durability, good skin affinity and good air permeability. In this paper, we present a simple and scalable porous piezoresistive/capacitive dual-mode sensor with a porous structure in polydimethylsiloxane (PDMS) and with multi-walled carbon nanotubes (MWCNTs) embedded on its internal surface to form a three-dimensional spherical-shell-structured conductive network. Thanks to the unique spherical-shell conductive network of MWCNTs and the uniform elastic deformation of the cross-linked PDMS porous structure under compression, our sensor offers a dual piezoresistive/capacitive strain-sensing capability, a wide pressure response range (1–520 kPa), a very large linear response region (95%), excellent response stability and durability (98% of initial performance after 1000 compression cycles). Multi-walled carbon nanotubes were coated on the surface of refined sugar particles by continuous agitation. Ultrasonic PDMS solidified with crystals was attached to the multi-walled carbon nanotubes. After the crystals were dissolved, the multi-walled carbon nanotubes were attached to the porous surface of the PDMS, forming a three-dimensional spherical-shell-structure network. The porosity of the porous PDMS was 53.9%. The large linear induction range was mainly related to the good conductive network of the MWCNTs in the porous structure of the crosslinked PDMS and the elasticity of the material, which ensured the uniform deformation of the porous structure under compression. The porous conductive polymer flexible sensor prepared by us can be assembled into a wearable sensor with good human motion detection ability. For example, human movement can be detected by responding to stress in the joints of the fingers, elbows, knees, plantar, etc., during movement. Finally, our sensors can also be used for simple gesture and sign language recognition, as well as speech recognition by monitoring facial muscle activity. This can play a role in improving communication and the transfer of information between people, especially in facilitating the lives of people with disabilities.
Wearable sensors open unprecedented opportunities for long-term health monitoring and human–machine interaction. Electrospinning is considered to be an ideal technology to produce functional structures for wearable sensors because of its unique merits to endow devices with highly designable functional microstructures, outstanding breathability, biocompatibility, and comfort, as well as its low cost, simple process flow, and high productivity. Recent advances in wearable sensors with one-, two-, or three-dimensional (1D, 2D, or 3D) electrospun microstructures have promoted various applications in healthcare, action monitoring, and physiological information recognition. Particularly, the development of various novel electrospun microstructures different from conventional micro/nanofibrous structures further enhances the electrical, mechanical, thermal, and optical performances of wearable sensors and provides them with multiple detection functions and superior practicality. In this review, we discuss (i) the principle and typical apparatus of electrospinning, (ii) 1D, 2D, and 3D electrospun microstructures for wearable sensing and their construction strategies and physical properties, (iii) applications of microstructured electrospun wearable devices in sensing pressure, temperature, humidity, gas, biochemical molecules, and light, and (iv) challenges of future electrospun wearable sensors for physiological signal recognition, behavior monitoring, personal protection, and health diagnosis.
Physical sensors have emerged as a promising technology for real‐time healthcare monitoring, which tracks various physical signals from the human body. Accurate acquisition of these physical signals from biological tissue requires excellent electrical conductivity and long‐term durability of the sensors under complex mechanical deformation. Conductive polymers, combining the advantages of conventional polymers and organic conductors, are considered ideal conductive materials for healthcare physical sensors due to their intrinsic conductive network, tunable mechanical properties, and easy processing. Doping engineering has been proposed as an effective approach to enhance the sensitivity, lower the detection limit, and widen the operational range of sensors based on conductive polymers. This approach enables the introduction of dopants into conductive polymers to adjust and control the microstructure and energy levels of conductive polymers, thereby optimizing their mechanical and conductivity properties. This review article provides a comprehensive overview of doping engineering methods to improve the physical properties of conductive polymers and highlights their applications in the field of healthcare physical sensors, including temperature sensors, strain sensors, stress sensors, and electrophysiological sensing. Additionally, the challenges and opportunities associated with conductive polymer‐based physical sensors in healthcare monitoring are discussed.This article is protected by copyright. All rights reserved
Microfluidics has recently received more and more attention in applications such as biomedical, chemical and medicine. With the development of microelectronics technology as well as material science in recent years, microfluidic devices have made great progress. Porous structures as a discontinuous medium in which the special flow phenomena of fluids lead to their potential and special applications in microfluidics offer a unique way to develop completely new microfluidic chips. In this article, we firstly introduce the fabrication methods for porous structures of different materials. Then, the physical effects of microfluid flow in porous media and their related physical models are discussed. Finally, the state-of-the-art porous microfluidic chips and their applications in biomedicine are summarized, and we present the current problems and future directions in this field.
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