Flexible Wearable Electronics Research Articles

Bio-Skin-Inspired Flexible Pressure Sensor Based on Carbonized Cotton Fabric for Human Activity Monitoring.

With the development of technology, people's demand for pressure sensors with high sensitivity and a wide working range is increasing. An effective way to achieve this goal is simulating human skin. Herein, we propose a facile, low-cost, and reproducible method for preparing a skin-like multi-layer flexible pressure sensor (MFPS) device with high sensitivity (5.51 kPa-1 from 0 to 30 kPa) and wide working pressure range (0-200 kPa) by assembling carbonized fabrics and micro-wrinkle-structured Ag@rGO electrodes layer by layer. In addition, the highly imitated skin structure also provides the device with an extremely short response time (60/90 ms) and stable durability (over 3000 cycles). Importantly, we integrated multiple sensor devices into gloves to monitor finger movements and behaviors. In summary, the skin-like MFPS device has significant potential for real-time monitoring of human activities in the field of flexible wearable electronics and human-machine interaction.

High-Performance Bifunctional Electrocatalysts for Flexible and Rechargeable Zn-Air Batteries: Recent Advances.

Flexible rechargeable Zn-air batteries (FZABs) exhibit high energy density, ultra-thin, lightweight, green, and safe features, and are considered as one of the ideal power sources for flexible wearable electronics. However, the slow and high overpotential oxygen reaction at the air cathode has become one of the key factors restricting the development of FZABs. The improvement of activity and stability of bifunctional catalysts has become a top priority. At the same time, FZABs should maintain the battery performance under different bending and twisting conditions, and the design of the overall structure of FZABs is also important. Based on the understanding of the three typical configurations and working principles of FZABs, this work highlights two common strategies for applying bifunctional catalysts to FZABs: 1) powder-based flexible air cathode and 2) flexible self-supported air cathode. It summarizes the recent advances in bifunctional oxygen electrocatalysts and explores the various types of catalyst structures as well as the related mechanistic understanding. Based on the latest catalyst research advances, this paper introduces and discusses various structure modulation strategies and expects to guide the synthesis and preparation of efficient bifunctional catalysts. Finally, the current status and challenges of bifunctional catalyst research in FZABs are summarized.

High Ion-Conducting PVA Nanocomposite Hydrogel-Based Wearable Piezoelectric and Triboelectric Sensors for Harsh Environments.

Traditional hydrogel-based wearable sensors with flexibility, biocompatibility, and mechanical compliance exhibit potential applications in flexible wearable electronics. However, the low sensitivity and poor environmental resistance of traditional hydrogels severely limit their practical application. Herein, high-ion-conducting poly(vinyl alcohol) (PVA) nanocomposite hydrogels were fabricated and applied for harsh environments. MXene ion-conducting microchannels and poly(sodium 4-styrenesulfonate) ion sources contributed to the directional transport of abundant free ions in the hydrogel, which significantly improved the sensitivity and mechanical-electric conversion of the nanocomposite hydrogel-based piezoelectric and triboelectric sensors. More importantly, the glycerol as an antifreezing agent enabled the hydrogel-based sensors to function in harsh environments. Therefore, the nanocomposite hydrogel exhibited high gauge factor (GF) at -20 °C (GF = 3.37) and 60 °C (GF = 3.62), enabling the hydrogel-based sensor to distinguish different writing letters and sounding words. Meanwhile, the hydrogel-based piezoelectric and triboelectric generators showed excellent mechanical-electric conversion performance regardless of low- (-20 °C) or high- (60 °C) temperature environments, which can be applied as a visual feedback system for information transmission without external power sources. This work provides self-powered nanocomposite hydrogel-based sensors that exhibit potential applications in flexible wearable electronics under harsh environmental conditions.

A conductive and anti-freezing gelatin-PAA-based organic hydrogel (PC-OH) with high adhesion and self-healing activities for wearable electronics

In the realm of flexible wearable electronics and interactive technologies, the adhesive and touch-sensing properties of materials play a crucial role, especially soft ionic conductors. However, these materials face several challenges in practical application, including structural damage, loss of functionality, and device stratification, particularly in extreme environments. To address this, a novel multifunctional organic hydrogel, termed PC-OH, was designed and prepared to enhance its performance. The hydrogel exhibits self-adhesion, self-healing, anti-freezing, anti-drying, and conductive capabilities. It demonstrates outstanding self-adhesive properties on skin surfaces under air (approximately 967 J/m2) or underwater (approximately 428 J/m2) conditions, with high transparency (visible light transmittance of 87 %), anti-freezing capability (−60 °C), anti-drying capability (60 °C), rapid self-healing in air or water (within 4 s), long-term stability over a wide temperature range (−20 °C to 60 °C for up to 7 days), high extensibility (up to ∼1700 % at 60 °C and ∼1200 % at −20 °C), and conductivity over a broad temperature range (ionic conductivity of 1.93 S m−1 at 60 °C and 3.13 × 10-3 S m−1 at −30 °C). Based on these properties of PC-OH hydrogel, we constructed a capacitive touch system to demonstrate its practical application. The touch panel features high stretchability, transparency, anti-freezing, anti-dehydration, self-healing, and self-adhesive human–machine interface capabilities, enabling integration with the skin under abnormal temperature and humidity conditions. Tasks such as writing text, drawing graphics, and playing electronic games validated the significant potential of the hydrogel in touch panels, providing a solution to long-standing issues of adhesion and tactile sensing.

Recent advances of sweat sampling, sensing, energy-harvesting and data-display toward flexible sweat electronics

Sweat contains diverse types of biomarkers that can mirror an individual’s health condition. The forefront research of sweat monitoring primarily focuses on sensing basic parameters, i.e., sweat rate and single electrolyte imbalances in controlled laboratory settings. However, recent works show the potential of sweat for the rich biomarkers in aspects of comprehensive health status display, timely safety alarming, and energy harvesting. The advances in wearable flexible electronics enable continuous, real-time, noninvasive detection of multiple sweat components, providing molecular-level insights into human physiology and psychology information; additionally, the efficient sweat extraction technologies of flexible electronics promote its application in energy harvesting, contributing to advancing a flexible sweat platform. This review comprehensively explores flexible sweat-based electronics, encompassing four key aspects: sweat sampling methods, sweat-based sensors, sweat-based energy harvesters, and sweat data display methods. Firstly, the traditional sweat-based platform is discussed in sweat sampling, sensing, and data analysis. Then, the development of wearable sweat sampling methods is discussed with a comparison of the traditional sweat collection methods. After that, the recent advances in sweat-based biosensors for monitoring diverse sweat analytes, such as the perspiration volume, glucose, lactate, and uric acid levels, are summarized. Subsequently, this review also highlights the recent progress and potential value of sweat-based energy harvesters in sweat-activated batteries and bio-fuel cells. Furthermore, multiple data display methods are proposed to achieve accurate feedback on health status, such as colorimetric techniques, light-emitting diodes, actuators, etc. Finally, this review concludes the main current challenges faced in practical applications of sweat-based bioelectronic systems and proposes a vision for the future evolution of this promising field.

Design of Stretchable and Conductive Self-Adhesive Hydrogels as Flexible Sensors by Guar-Gum-Enabled Dynamic Interactions.

The limited elasticity and inadequate bonding of hydrogels made from guar gum (GG) significantly hinder their widespread implementation in personalized wearable flexible electronics. In this study, we devise GG-based self-adhesive hydrogels by creating an interpenetrating network of GG cross-linked with acrylic, 4-vinylphenylboronic acid, and Ca2+. With the leverage of the dynamic interactions (hydrogen bonds, borate ester bonds, and coordination bonds) between -OH in GG and monomers, the hydrogel exhibits a high stretchability of 700%, superior mechanical stress of 110 kPa, and robust adherence to several substrates. The adhesion strength of 54 kPa on porcine skin is obtained. Furthermore, the self-adhesive hydrogel possesses stable conductivity, an elevated gauge factor (GF), and commendable durability. It can be affixed to the human body as a strain sensor to obtain precise monitoring of human movement behavior. Our research offers possibilities for the development of GG-based hydrogels and applications in wearable electronics and medical monitoring.

Recyclable and mechanically tough nanocellulose reinforced natural rubber composite conductive elastomers for flexible multifunctional sensor

The development of flexible wearable multifunctional electronics has gained great attention in the field of human motion monitoring. However, developing mechanically tough, highly stretchable, and recyclable composite conductive materials for application in multifunctional sensors remained great challenges. In this work, a mechanically tough, highly stretchable, and recyclable composite conductive elastomer with the dynamic physical-chemical dual-crosslinking network was fabricated by the combination of multiple hydrogen bonds and dynamic ester bonds. To prepare the proposed composite elastomers, the polyaniline-modified carboxylate cellulose nanocrystals (C-CNC@PANI) were used as both conductive filler to yield high conductivity of 15.08 mS/m, and mechanical reinforcement to construct the dynamic dual-crosslinking network with epoxidized natural rubber latex to realize the high mechanical strength (8.65 MPa) and toughness (29.57 MJ/m3). Meanwhile, the construction of dynamic dual-crosslinking network endowed the elastomer with satisfactory recyclability. Based on these features, the composite conductive elastomers were used as strain sensors, and electrode material for assembling flexible and recyclable self-powered sensors for monitoring human motions. Importantly, the composite conductive elastomers maintained reliable sensing and energy harvesting performance even after multiple recycling process. This study provides a new strategy for the preparation of recyclable, mechanically tough composite conductive materials for wearable sensors.

Flexible piezoresistive pressure sensor based on a graphene-carbon nanotube-polydimethylsiloxane composite

Flexible sensors are used widely in wearable devices, specifically flexible piezoresistive sensors, which are common and easy to manipulate. However, fabricating such sensors is expensive and complex, so proposed here is a simple fabrication approach involving a sensor containing microstructures replicated from a sandpaper template onto which polydimethylsiloxane containing a mixture of graphene and carbon nanotubes is spin coated. The surface morphologies of three versions of the sensor made using different grades of sandpaper are observed, and the corresponding pressure sensitivities and linearity and hysteresis characteristics are assessed and analyzed. The results show that the sensor made using 80-mesh sandpaper has the best sensing performance. Its sensitivity is 0.341 kPa−1 in the loading range of 0–1.6 kPa, it responds to small external loading of 100 Pa with a resistance change of 10%, its loading and unloading response times are 0.126 and 0.2 s, respectively, and its hysteresis characteristic is ∼7%, indicating that the sensor has high sensitivity, fast response, and good stability. Thus, the presented piezoresistive sensor is promising for practical applications in flexible wearable electronics.

Flexible Aerogel Materials: A Review on Revolutionary Flexibility Strategies and the Multifunctional Applications.

The design and preparation of flexible aerogel materials with high deformability and versatility have become an emerging research topic in the aerogel fields, as the brittle nature of traditional aerogels severely affects their safety and reliability in use. Herein, we review the preparation methods and properties of flexible aerogels and summarize the various controlling and design methods of aerogels to overcome the fragility caused by high porosity and nanoporous network structure. The mechanical flexibility of aerogels can be revolutionarily improved by monomer regulation, nanofiber assembly, structural design and controlling, and constructing of aerogel composites, which can greatly broaden the multifunctionality and practical application prospects. The design and construction criterion of aerogel flexibility is summarized: constructing a flexible and deformable microstructure in an aerogel matrix. Besides, the derived multifunctional applications in the fields of flexible thermal insulation (flexible thermal protection at extreme temperatures), flexible wearable electronics (flexible sensors, flexible electrodes, electromagnetic shielding, and wave absorption), and environmental protection (oil/water separation and air filtration) are summarized. Furthermore, the future development prospects and challenges of flexible aerogel materials are also summarized. This review will provide a comprehensive research basis and guidance for the structural design, fabrication methods, and potential applications of flexible aerogels.

Fully Polymeric Conductive Hydrogels with Low Hysteresis and High Toughness as Multi‐Responsive and Self‐Powered Wearable Sensors

AbstractHigh mechanical strength, excellent toughness, low hysteresis, and robust resilience are of great importance for stretchable conductive hydrogels (CHs) to heighten their reliabilities for self‐powered sensing applications. However, it still remains challenging to simultaneously obtain the mutually exclusive performances. Herein, an intrinsically conductive and adhesive hydrogel is fabricated by one‐step radical polymerization of acrylamide (AAm), three hydroxy groups together clustered‐N‐[tris(hydroxymethyl)methyl]acrylamide (THMA), and cationic 1‐Butyl‐3‐Vinylimidazolium Bromide (ILs) dissolved in core‐shell structurally dispersed PEDOT:PSS (PP) solution. Owing to abundant clustered hydrogen bonds, electrostatic interactions between PILs chains and anionic PSS shells, and polymer chain entanglements, the CHs feature superior mechanical properties with a high tensile strength (0.25 MPa), fracture strain (1015%), fracture toughness (1.22 MJ m‐3), fracture energy of 36.5 kJ m‐2 and extremely low hysteresis (5%), and display excellent resilience and fatigue resistance. As a result, the CHs indicate excellent sensing properties with a gauge factor up to 10.46, a broad sensing range of strain (1‐900%) and pressure (0.05‐100 kPa), and fast responsive rate, thus qualifying for monitoring reliably and accurately large and tiny human movements in daily life. Moreover, the hydrogel‐assembled triboelectric nanogenerators (TENGs) exhibit excellent and stable electrical output performances, which are greatly promising in self‐powered flexible wearable electronics.

Interfacial-engineered robust and high performance flexible polylactic acid/polyaniline/MXene electrodes for high-perfarmance supercapacitors

Flexible supercapacitors with high mechanical strength, excellent flexibility, and high performance are highly desired to meet the increasing demands of flexible electronics. However, the trade-off between mechanical and electrochemical properties remains challenging. In this context, an interface-engineered strategy approach was proposed to construct polylactic acid (PLA)/polyaniline (PANI)/MXene (PPM) film electrodes for flexible supercapacitor applications. In the PPM electrode, the porous PLA prepared from the nonsolvent-induced-phase-separation method served as an ideal flexible substrate, providing excellent flexibility and high mechanical strength, whereas PANI as the coupling agent, enhanced the interfacial strength between PLA and the electroactive MXene that was firmly anchored and deposited on PLA through a facile layer-by-layer dip coating method. The tensile strength at break, elongation at break, and toughness of PPM are 53.09 MPa, 11.09 %, and 4.12 MJ/m3, respectively, much higher than those of pure MXene (29.36 MPa, 4.62 %, and 0.75 MJ/m3). At an optimum mass loading density of 3 mg cm−2 for MXene, the fabricated PPM3 film electrode achieved a high specific capacitance of 290.8 F g−1 at a current density of 1 A g−1 in the three-electrode setup, approximately 1.5 times that of 190.8 F g−1 for pure MXene. Meanwhile, the symmetric all-solid-state supercapacitor based on PPM3 film electrodes delivers a high specific capacitance of 193.7 F g−1 at a current density of 0.25 A g−1, with a corresponding high energy density of 9.3 Wh kg−1 at a power density of 291.3 W kg−1. The SC retains 86 % of its original capacitance even bent at 120° and also possesses an excellent fire-retardant ability, demonstrating its great potential for flexible and safe wearable electronics.

Triboelectrically active hydrogel drives self-charging zinc-ion battery and human motion sensing

The fast advancement of flexible electronic technology hastens an ever-growing demand for power sources that are adaptable and flexible, and the arrival of innovative energy harvesting technologies such as triboelectric nanogenerator (TENG) further endow the potable electronics with versatility and sustainability. Herein, polyvinyl alcohol/ polyacrylamide/ zinc sulfate (PPZ) hydrogel was synthesized via an one-step UV-initiated polymerization. The hydrogel demonstrates exceptional tensile properties (with a large strain of 915 % and a corresponding tensile strength of 231 KPa), excellent electrical conductivity and light transmittance. A highly flexible and easily adaptable single-electrode TENG was thus fabricated on the base of the as-synthetized PPZ (PPZ-TENG), where the PPZ hydrogel functions as both the charging layer and current collector. While promoting a high electrical output performance of the PPZ-TENG (an open circuit voltage of 176 V and a power density of 328 mW/m2), the PPZ hydrogel also serves as an efficient ion-conductive electrolyte to construct highly flexible self-charging zinc ion batteries (ZIBs). Besides, highly sensitive strain response toward environmental stimuli was also demonstrated, which makes the integration strategy a promising solution for future development self-powered flexible wearable electronics toward the sustainable monitoring of human vital signs such as pulse and limb movement.

Tunable durian seed gum-derived eutectogel as a novel coating material: Rheological, thermal, textural and barrier properties for enhanced food preservation

As a promising green and sustainable coating material, gum was extracted from durian seed to produce eutectogel, which the properties were tunable using natural deep eutectic solvent (NADES). Ten different eutectogels were successfully synthesized using durian seed gum (DSG) and xanthan gum (XG) gelators at different composition (5, 10, 15 %) to gel choline chloride-glucose (1:1), choline chloride-fructose (1:2) and betaine-glucose-water (1:1:1) NADESs. Results revealed that eutectogel was non-Newtonian and weak gel material with excellent thermostability up to 200 °C. When the gum content increased, the resulted eutectogel showed higher viscosity, yield stress, hardness, gumminess, adhesiveness, and weight holding capacity. In overall, choline chloride-fructose (1:2) NADES and 10 % of DSG formed an excellent eutectogel which remained stable and compatible upon 12 weeks of storage. It displayed superior viscoelastic, texture, gases and moisture barrier properties which were beneficial for food coating application. This eutectogel was able to extend the shelf life of fresh-cut apples during storage with lower weight loss and higher total phenolic content (TPC). The potential future of this well-characterized tunable DSG-derived eutectogel includes, but not limited to, food and pharmaceutical industries, smart sensing, flexible wearable electronics, water purification, supercapacitors and batteries.

A new In Situ Oxidized 2D Layered MnBi2Te4 Cathode for High-Performance Aqueous Zinc-Ion Battery.

Recently, aqueous zinc ion batteries (AZIBs) with the superior theoretical capacity, high safety, low prices, and environmental protection, have emerged as a contender for advanced energy storage. However, challenges related to cathode materials, such as dissolution, instability, and structural collapse, have hindered the progress of AZIBs. Here, a novel AZIB is constructed using an oxidized 2D layered MnBi2Te4 cathode for the first time. The oxidized MnBi2Te4 cathode with large interlayer spacing and low energy barrier for zinc ion diffusion at 240°C, exhibited impressive characteristics, including a high reversibility capacity of 393.1mAhg-1 (0.4Ag-1), outstanding rate performance, and long cycle stability. Moreover, the corresponding aqueous button cell also exhibits excellent electrochemical performance. To demonstrate the application in practice in the realm of flexible wearable electronics, a quasi-solid-state micro ZIB (MZIB) is constructed and shows excellent flexibility and high-temperature stability (the capacity does not significantly degrade when the temperature reaches 100°C and the bending angle exceeds 150°). This research offers effective tactics for creating high-performance cathode materials for AZIBs.

Anti-freezing and moisturizing PAA/PEDOT: PSS ionogels with multiple stimulus responses for flexible wearable electronics

Hydrogel is a promising material for wearable electronics due to its good mechanical properties, electrical conductivity and body adaptability. However, subzero freezing and water loss under high temperature or prolonged placement are great challenges for hydrogels. Here, polyacrylic acid / poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PAA/PEDOT: PSS) ionogels were designed by entangling PAA and PEDOT: PSS chains with each other in a binary solvent system of water and ionic liquid (IL) and chemical cross-linking by N, N’-methylene bisacrylamide (MBA). It has excellent mechanical properties (8.3 kPa, > 500 %), skin-adapted Young's modulus (<10 kPa), high conductivity (8.06 S·m−1), and strong adhesion (13.3 kPa). Ionogel has a sensitive response as a sensor (GF = 2.08, 0–200 %; GF = 3.64, 200–400 %; GF = 4.58, 400–510 %). Especially, the freeze-resistance and long-term moisturizing properties make ionogels exhibit long-lasting and robust utility. As a scalable application platform, we demonstrate the potential applications of this novel ionogel as a body-conformable electronic product in a series of conceptual demonstrations, including full range of human motion response, human–machine interaction (HMI), temperature signal detection and TENG device assembly.

High‐Performance Nd: AIZO/Al2O3 Dual Active Layer Design Without Thermal Annealing: High‐Speed Electron Transport and Defect Modification in Thin Film Transistors

Flexible wearable electronics have been developing rapidly in recent years, and one of its core devices, thin‐film transistor (TFT), is also attracting attention. Current TFT preparation processes usually require high annealing temperatures (&gt;350 °C), which is not conducive to their application on most flexible substrates (PET, PEN, nanopaper, etc.). In this article, a strategy for the room temperature preparation of Nd:AIZO/Al2O3 dual‐layer TFT devices is proposed, which has appreciable electrical properties without additional annealing treatment. Taguchi orthogonal experimental methods are used to investigate the effects of three essential process parameters on the performance of the films and devices. As Nd:AIZO deposition time decreases and Al2O3 oxygen percentage and time during deposition increase, the μsat and SS of TFT devices are improved. With the preferred combination of parameters applied to the device preparation, the device exhibits a saturation mobility μsat of 24.3 cm2 V−1 s−1, a threshold voltage Vth of −1.4 V, a subthreshold swing SS of 0.21 V decade−1 and an Ion/Ioff ratio of 4.26 × 108. The ultra‐thin Al2O3 layer act as defect modification and form high‐speed electron transport in channel layer. The room temperature preparation of the dual‐layer TFT process proposed in this article is compatible with large‐size low‐cost flexible substrates. It has great potential for application in green flexible wearable electronics.

Stretchable and Highly Sensitive Flexible Strain Sensor Based on a Three‐Layer Core–Shell Structure of Polydopamine/Polypyrrole@Natural Rubber for Human Activity Monitoring

In recent years, flexible strain sensors with a wide detection range and high sensitivity have garnered significant attention for human health monitoring. However, fabricating strain sensors with a broad strain range while retaining high sensitivity remains a major challenge. Herein, a green and facile method is successfully developed to fabricate the polydopamine/polypyrrole@natural rubber (PDA/PPy@NR)‐based strain sensor with a three‐layer core–shell structure. PDA and PPy are coated uniformly onto the surface of the NR nanosphere by in situ polymerization. The electromechanical and strain sensing properties of the fabricated composite are investigated. The homogeneous coating of PPy and PDA layers has facilitated the formation of continuous conductive pathways within the NR matrix, even at low loading levels. Consequently, the strain sensor exhibits remarkable sensitivity over a wide strain range (≈800%) and long‐term reliability (2500 cycles at 50%). The PDA/PPy@NR strain sensor shows an exceptionally high gauge factor value (142.6) and a short response time (125 ms). Furthermore, this PDA/PPy@NR strain sensor can effectively detect and capture subtle and large human movements such as limb joints and facial movements as well as even distinguish the pronunciation of different words. The PDA/PPy@NR strain sensor holds great promise for integration into flexible wearable electronics.

Bioinspired breathable biodegradable bioelastomer-based flexible wearable electronics for high-sensitivity human-interactive sensing

Flexible wearable electronic sensors are regarded to facilitate revolutionary changes in human's daily life for their great promise in multifunctional artificial electronic skins, personalized healthcare monitoring, and smart human–machine interaction. However, there remains great challenges to simultaneously achieve high sensitivity, broad sensing range and robust cyclic stability for high-performance personal diagnostic healthcare monitoring, excellent breathability for comfortable wearing, as well as environmentally friendly biodegradability for reducing electronic wastes. Herein, bioinspired by three-dimensional network structure of ant nest with high specific surface area, interconnected channels, and robust ventilation, a wearable, breathable, and biodegradable electronic sensor is prepared from facile face-to-face assembly of breathable biodegradable MXene-coated poly(1,8-octanediol-co-polycaprolactone citrate) elastomer sponge (MXene@POPLC), and an MXene ink-printed interdigitated electrode-coated breathable electrospun film. The as-obtained flexible electronic sensor exhibits high sensitivity (up to 246.3 kPa−1), broad sensing range (up to 333.3 kPa), reliable cycling stability (∼20,000 cycles), fast response (10 ms)/recovery time, robust breathability, excellent biocompatibility, facile biodegradability, and wireless wearable human–machine interfacing. Therefore, this line of research work opens up a novel avenue for the preparation of multifunctional wearable, breathable, and biodegradable electronics to hold great promise in smart healthcare monitoring, intelligent human–machine interaction, smart personal protection and next-generation artificial skin.

Recent Advances in Flexible Wearable Technology: From Textile Fibers to Devices.

Smart textile fabrics have been widely investigated and used in flexible wearable electronics because of their unique structure, flexibility and breathability, which are highly desirable with integrated multifunctionality. Recent years have witnessed the rapid development of textile fiber-based flexible wearable devices. However, the pristine textile fibers still can't meet the high standards for practical flexible wearable devices, which calls for the development of some effective modification strategies. In this review, we summarize the recent advances in the flexible wearable devices based on the textile fibers, putting special emphasis on the design and modifications of textile fibers. In addition, the applications of textile fibers in various fields and the critical role of textile fibers are also systematically discussed, which include the supercapacitors, sensors, triboelectric nanogenerators, thermoelectrics, and other self-powered electronic devices. Finally, the main challenges that should be overcome and some effective solutions are also manifested, which will guide the future development of more effective textile fiber-based flexible wearable devices.

Dry‐Wet Hybrid Direct Printing of Laser‐Induced Graphene and Zinc Oxide Nanoribbons for Continuous‐Flow Manufacturing of Flexible Wearable Photodetectors

AbstractFlexible wearable electronics enable an in situ and real‐time measurement of human physiology and micro‐environment. Although large‐scale production of flexible wearable electronics is demonstrated using direct printing techniques, the “wet” nature of these techniques requires multiple procedures and chemicals to prepare printable inks, increasing the complexity and cost. Here, a dry‐wet hybrid direct printing is developed for the mass production of flexible wearable photodetectors, in which a “dry” direct laser writing and a “wet” screen printing are employed to fabricate laser‐induced graphene as electrode layer and zinc oxide as photosensitive layer, respectively. The liquid‐free fabrication of LIG significantly reduces the complexity and cost of the production. An automatic conveyor belt is designed to realize continuous‐flow manufacturing. The photodetectors demonstrate good ultraviolet (UV) photodetection performances, such as a photo‐to‐dark current ratio (Iphoto/Idark) of 5.67 × 105, approaching the record of similar devices. The manufacturing system presents a high reproducibility, considering that Iphoto/Idark only fluctuates within 7.10%. The flexible photodetectors are worn as wristbands after being integrated with a data acquisition and transmission circuit. UV intensity is real‐time monitored on a self‐developed mobile application. The continuous‐flow manufacturing based on the developed dry‐wet hybrid direct printing sheds light on the mass production of flexible wearable electronics.