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Thorough understanding of how to control cell behaviors including cell adhesion, orientation, migration and differentiation on an artificial surface is critical in materials and life ...sciences such as advanced biomedical engineering, tissue engineering, and cell-based bioassay. In nature, extracellular matrix (ECM) plays an important role in controlling cell behaviors. It can not only provide the cells with mechanical support but also profoundly affect cell functions such as metabolism, movement and transport process. Functional polymer surface exhibits superior advantages over many other materials for use as artificial ECM owing to its excellent mechanical properties, abundant chemical species and remarkable capability to form various topographical surfaces. In particular, surface chemistry, mechanical properties and topography of these functional polymers are found to be three major parameters for effective control of cell behaviors. This paper comprehensively reviews the fundamental understanding of functional polymer surfaces for controlling cell behaviors. Different fabrication methods to achieve functional polymer surfaces and the parameters for effective control of cell behaviors are discussed. The future prospects and challenges particularly in cell biomedical engineering are also discussed at the end of this review paper.
3D-printing tough conductive hydrogels (TCHs) with complex structures is still a challenging task in related fields due to their inherent contrasting multinetworks, uncontrollable and slow ...polymerization of conductive components. Here we report an orthogonal photochemistry-assisted printing (OPAP) strategy to make 3D TCHs in one-pot via the combination of rational visible-light-chemistry design and reliable extrusion printing technique. This orthogonal chemistry is rapid, controllable, and simultaneously achieve the photopolymerization of EDOT and phenol-coupling reaction, leading to the construction of tough hydrogels in a short time (t
~30 s). As-prepared TCHs are tough, conductive, stretchable, and anti-freezing. This template-free 3D printing can process TCHs to arbitrary structures during the fabrication process. To further demonstrate the merits of this simple OPAP strategy and TCHs, 3D-printed TCHs hydrogel arrays and helical lines, as proofs-of-concept, are made to assemble high-performance pressure sensors and a temperature-responsive actuator. It is anticipated that this one-pot rapid, controllable OPAP strategy opens new horizons to tough hydrogels.
High performance photodetectors play important roles in the development of innovative technologies in many fields, including medicine, display and imaging, military, optical communication, ...environment monitoring, security check, scientific research and industrial processing control. Graphene, the most fascinating two‐dimensional material, has demonstrated promising applications in various types of photodetectors from terahertz to ultraviolet, due to its ultrahigh carrier mobility and light absorption in broad wavelength range. Graphene field effect transistors are recognized as a type of excellent transducers for photodetection thanks to the inherent amplification function of the transistors, the feasibility of miniaturization and the unique properties of graphene. In this review, we will introduce the applications of graphene transistors as photodetectors in different wavelength ranges including terahertz, infrared, visible, and ultraviolet, focusing on the device design, physics and photosensitive performance. Since the device properties are closely related to the quality of graphene, the devices based on graphene prepared with different methods will be addressed separately with a view to demonstrating more clearly their advantages and shortcomings in practical applications. It is expected that highly sensitive photodetectors based on graphene transistors will find important applications in many emerging areas especially flexible, wearable, printable or transparent electronics and high frequency communications.
Graphene demonstrates promising applications in various types of photodetectors from terahertz to ultraviolet, due to its ultrahigh carrier mobility and light absorption in a broad wavelength range. Graphene field effect transistors are recognized as a type of excellent transducers for photodetection thanks to the inherent amplification function of the transistors, the feasibility of miniaturization, and the unique properties of graphene.
One-dimensional flexible supercapacitor yarns are of considerable interest for future wearable electronics. The bottleneck in this field is how to develop devices of high energy and power density, by ...using economically viable materials and scalable fabrication technologies. Here we report a hierarchical graphene-metallic textile composite electrode concept to address this challenge. The hierarchical composite electrodes consist of low-cost graphene sheets immobilized on the surface of Ni-coated cotton yarns, which are fabricated by highly scalable electroless deposition of Ni and electrochemical deposition of graphene on commercial cotton yarns. Remarkably, the volumetric energy density and power density of the all solid-state supercapacitor yarn made of one pair of these composite electrodes are 6.1 mWh cm(-3) and 1,400 mW cm(-3), respectively. In addition, this SC yarn is lightweight, highly flexible, strong, durable in life cycle and bending fatigue tests, and integratable into various wearable electronic devices.
Stretchable electronics find widespread uses in a variety of applications such as wearable electronics, on-skin electronics, soft robotics and bioelectronics. Stretchable electronic devices ...conventionally built with elastomeric thin films show a lack of permeability, which not only impedes wearing comfort and creates skin inflammation over long-term wearing but also limits the design form factors of device integration in the vertical direction. Here, we report a stretchable conductor that is fabricated by simply coating or printing liquid metal onto an electrospun elastomeric fibre mat. We call this stretchable conductor a liquid-metal fibre mat. Liquid metal hanging among the elastomeric fibres self-organizes into a laterally mesh-like and vertically buckled structure, which offers simultaneously high permeability, stretchability, conductivity and electrical stability. Furthermore, the liquid-metal fibre mat shows good biocompatibility and smart adaptiveness to omnidirectional stretching over 1,800% strain. We demonstrate the use of a liquid-metal fibre mat as a building block to realize highly permeable, multifunctional monolithic stretchable electronics.
Lithium batteries are key components of portable devices and electric vehicles due to their high energy density and long cycle life. To meet the increasing requirements of electric devices, however, ...energy density of Li batteries needs to be further improved. Anode materials, as a key component of the Li batteries, have a remarkable effect on the increase of the overall energy density. At present, various anode materials including Li anodes, high‐capacity alloy‐type anode materials, phosphorus‐based anodes, and silicon anodes have shown great potential for Li batteries. Composite‐structure anode materials will be further developed to cater to the growing demands for electrochemical storage devices with high‐energy‐density and high‐power‐density. In this review, the latest progress in the development of high‐energy Li batteries focusing on high‐energy‐capacity anode materials has been summarized in detail. In addition, the challenges for the rational design of current Li battery anodes and the future trends are also presented.
The increasing development of battery‐powered vehicles for exceeding 500 km endurance has stimulated the exploration of lithium‐ion batteries with high‐energy‐density and high‐power‐density. In this review, proximate developments in various types of high specific energy lithium‐ion batteries are screened, focusing on silicon‐based anode, phosphorus‐based anode, lithium metal anode, and hybrid anode systems.
High‐performance supercapacitors (SCs) are promising energy storage devices to meet the pressing demand for future wearable applications. Because the surface area of a human body is limited to 2 m2, ...the key challenge in this field is how to realize a high areal capacitance for SCs, while achieving rapid charging, good capacitive retention, flexibility, and waterproofing. To address this challenge, low‐cost materials are used including multiwall carbon nanotube (MWCNT), reduced graphene oxide (RGO), and metallic textiles to fabricate composite fabric electrodes, in which MWCNT and RGO are alternatively vacuum‐filtrated directly onto Ni‐coated cotton fabrics. The composite fabric electrodes display typical electrical double layer capacitor behavior, and reach an ultrahigh areal capacitance up to 6.2 F cm−2 at a high areal current density of 20 mA cm−2. All‐solid‐state fabric‐type SC devices made with the composite fabric electrodes and water‐repellent treatment can reach record‐breaking performance of 2.7 F cm−2 at 20 mA cm−2 at the first charge–discharge cycle, 3.2 F cm−2 after 10 000 charge–discharge cycles, zero capacitive decay after 10 000 bending tests, and 10 h continuous underwater operation. The SC devices are easy to assemble into tandem structures and integrate into garments by simple sewing.
A multiwall carbon nanotube/reduced graphene oxide composite fabric electrode with an ultrahigh areal capacitance of 6.2 F cm−2 is obtained by alternating filtration on Ni‐coated cotton fabric. With simple textile sewing and sealing techniques, these high‐performance electrodes are assembled into all‐solid‐state fabric‐type supercapacitor devices, which possess record‐breaking initial capacitance (2.7 F cm−2) and excellent retention, remarkable flexibility, and are waterproof.
Highlights
General principles for fiber functionalization and strain sensor fabrication are briefly reviewed.
Future application potentials of wearable strain sensors are summarized and evaluated.
...Challenges and perspectives of fiber-based wearable strain sensors are critically discussed.
Wearable strain sensors are arousing increasing research interests in recent years on account of their potentials in motion detection, personal and public healthcare, future entertainment, man–machine interaction, artificial intelligence, and so forth. Much research has focused on fiber-based sensors due to the appealing performance of fibers, including processing flexibility, wearing comfortability, outstanding lifetime and serviceability, low-cost and large-scale capacity. Herein, we review the latest advances in functionalization and device fabrication of fiber materials toward applications in fiber-based wearable strain sensors. We describe the approaches for preparing conductive fibers such as spinning, surface modification, and structural transformation. We also introduce the fabrication and sensing mechanisms of state-of-the-art sensors and analyze their merits and demerits. The applications toward motion detection, healthcare, man–machine interaction, future entertainment, and multifunctional sensing are summarized with typical examples. We finally critically analyze tough challenges and future remarks of fiber-based strain sensors, aiming to implement them in real applications.
Metal interconnects, contacts, and electrodes are indispensable elements for most applications of flexible, stretchable, and wearable electronics. Current fabrication methods for these metal ...conductors are mainly based on conventional microfabrication procedures that have been migrated from Si semiconductor industries, which face significant challenges for organic‐based compliant substrates. This Research News highlights a recently developed full‐solution processing strategy, polymer‐assisted metal deposition (PAMD), which is particularly suitable for the roll‐to‐roll, low‐cost fabrication of high‐performance compliant metal conductors (Cu, Ni, Ag, and Au) on a wide variety of organic substrates including plastics, elastomers, papers, and textiles. This paper presents i) the principles of PAMD, and how to use it for making ii) flexible, stretchable, and wearable conductive metal electrodes, iii) patterned metal interconnects, and d) 3D stretchable and compressible metal sponges. A critical perspective on this emerging strategy is also provided.
Polymer‐assisted metal deposition (PAMD) is a full‐solution processing strategy for fabricating high‐performance flexible, stretchable, compressible, and wearable metal conductors (Cu, Ni, Ag, and Au) on a wide variety of soft substrates—including plastics, elastomers, papers, polyurethane sponges, and textiles.
Solution-processed solar cells are appealing because of the low manufacturing cost, the good compatibility with flexible substrates, and the ease of large-scale fabrication. Whereas ...solution-processable active materials have been widely adopted for the fabrication of organic, dye-sensitized, and perovskite solar cells, vacuum-deposited transparent conducting oxides (TCOs) such as indium tin oxide, fluorine-doped tin oxide, and aluminum-doped tin oxide are still the most frequently used transparent electrodes (TEs) for solar cells. These TCOs not only significantly increase the manufacturing cost of the device, but also are too brittle for future flexible and wearable applications. Therefore, developing solution-processed TEs for solar cells is of great interest. This paper provides a detailed discussion on the recent development of solution-processed TEs, including the chemical synthesis of the electrode materials, the solution-based technologies for the electrode fabrication, the optical and electrical properties of the solution-processed TEs, and their applications on solar cells.
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