An Environment‑Tolerant Ion‑Conducting Double‑Network Composite Hydrogel for High‑Performance Flexible Electronic Devices

High-performance ion-conducting hydrogels(ICHs)are vital for developing flexible electronic devices.However,the robustness and ion-conducting behavior of ICHs deteriorate at extreme tempera-tures,hampering their use in soft electronics.To resolve these issues,a method involving freeze–thawing and ionizing radiation technology is reported herein for synthesizing a novel double-network(DN)ICH based on a poly(ionic liquid)/MXene/poly(vinyl alcohol)(PMP DN ICH)system.The well-designed ICH exhibits outstanding ionic conductivity(63.89 mS cm^(-1) at 25℃),excellent temperature resistance(-60–80℃),prolonged stability(30 d at ambient temperature),high oxidation resist-ance,remarkable antibacterial activity,decent mechanical performance,and adhesion.Additionally,the ICH performs effectively in a flexible wireless strain sensor,thermal sensor,all-solid-state supercapacitor,and single-electrode triboelectric nanogenerator,thereby highlighting its viability in constructing soft electronic devices.The highly integrated gel structure endows these flexible electronic devices with stable,reliable signal output performance.In particular,the all-solid-state supercapacitor containing the PMP DN ICH electrolyte exhibits a high areal specific capacitance of 253.38 mF cm^(-2)(current density,1 mA cm^(-2))and excellent environmental adaptability.This study paves the way for the design and fabrication of high-performance mul-tifunctional/flexible ICHs for wearable sensing,energy-storage,and energy-harvesting applications.

High-resolution flexible electronic devices by electrohydrodynamic jet printing:From materials toward applications

High-resolution flexible electronic devices are widely used in the fields of soft robotics,smart human-machine interaction,and intelligent e-healthcare monitoring due to their mechanical flexibility,ductility,and compactness.The electrohydrodynamic jet printing(e-jet printing)technique is used for constructing high-resolution and cross-scale flexible electronic devices such as field-effect transistors(FETs),flexible sensors,and flexible displays.As a result,researchers are paying close attention to e-jet printing flexible electronic devices.In this review,we focused on the latest advancements in high-resolution flexible electronics made by e-jet printing technology,including various materials used in e-jet printing inks,the process control of e-jet printing,and their applications.First,we summarized various functional ink materials available for e-jet printing,including organic,inorganic,and hybrid materials.Then,the interface controlling the progress of e-jet printing was discussed in detail,including the physical and chemical properties of the functional ink,the interfacial wettability between the ink and substrate,and the microdroplet injection behavior in a high-voltage field.Additionally,various applications of e-jet printing in the fields of flexible electrodes,FETs,flexible sensors,and flexible displays were demonstrated.Finally,the future problems and potential associated with the development of next generation e-jet printing technology for flexible electronic devices were also presented.

Adhesive hydrogels for bioelectronics

Benefiting from the unique advantages of superior biocompatibility,strong stability,good biodegradability,and adjustable mechanical properties,hydrogels have attracted extensive research interests in bioelectronics.However,due to the existence of an interface between hydrogels and human tissues,the transmission of electrical signals from the human tissues to the hydrogel electronic devices will be hindered.The adhesive hydrogels with adhesive properties can tightly combine with the human tissue,which can enhance the contact between the electronic devices and human tissues and reduce the contact resistance,thereby improving the performance of hydrogel electronic devices.In this review,we will discuss in detail the adhesion mechanism of adhesive hydrogels and elaborate on the design principles of adhesive hydrogels.After that,we will introduce some methods of performance evaluation for adhesive hydrogels.Finally,we will provide a perspective on the development of adhesive hydrogel bioelectronics.

Failure mechanisms in flexible electronics

The rapid evolution of flexible electronic devices promises to revolutionize numerous fields by expanding the applications of smart devices.Nevertheless,despite this vast potential,the reliability of these innovative devices currently falls short,especially in light of demanding operation environment and the intrinsic challenges associated with their fabrication techniques.The heterogeneity in these processes and environments gives rise to unique failure modes throughout the devices'lifespan.To significantly enhance the reliability of these devices and assure long-term performance,it is paramount to comprehend the underpinning failure mechanisms thoroughly,thereby,enabling,optimal design solutions.A myriad of investigative efforts have been dedicated to unravel these failure mechanisms,utilizing a spectrum of tools from analytical models,numerical methods,to advanced characterization methods.This review delves into the root causes of device failure,scrutinizing both the fabrication process and the operation environment.Next,We subsequently address the failure mechanisms across four commonly observed modes:strength failure,fatigue failure,interfacial failure,and electrical failure,followed by an overview of targeted characterization methods associated with each mechanism.Concluding with an outlook,we spotlight ongoing challenges and promising directions for future research in our pursuit of highly resilient flexible electronic devices.

Fabrication techniques and applications of flexible graphene-based electronic devices

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

Recent advances in flexible and wearable organic optoelectronic devices

Flexible and wearable optoelectronic devices have been developing to a new stage due to their unique capacity for the possibility of a variety of wearable intelligent electronics, including bendable smartphones, foldable touch screens and antennas, paper-like displays, and curved and flexible solid-state lighting devices. Before extensive commercial applications, some issues still have to be solved for flexible and wearable optoelectronic devices. In this regard, this review concludes the newly emerging flexible substrate materials, transparent conductive electrodes, device architectures and light manipulation methods. Examples of these components applied for various kinds of devices are also summarized. Finally, perspectives about the bright future of flexible and wearable electronic devices are proposed.

Development of flexible Li-ion batteries for flexible electronics

We provide a critical review on the recent development of flexible lithium-ion batteries(FLIBs)for flexible electronic devices.The innovative designs of cell configuration for bendable and stretchable FLIBs,selection of active materials,and evaluation methods for FLIBs are discussed.The grand challenges for FLIBs are energy density and scale-up fabrication as demonstrated in the review.Furthermore,the lack of quantitative evaluation methods for FLIBs'performance and nondestructive tools to probe the mechanical degradation may significantly hinder the development of FLIB technologies.Perspectives for future research directions,based on the current state of progress,are discussed.

A pseudocapacitive molecule-induced strategy to construct flexible high-performance asymmetric supercapacitors

The combination of high-voltage windows and bending stability remains a challenge for supercapacitors.Here,we present an“advantage-complementary strategy”using sodium lignosulfonate as a pseudocapacitive molecule to regulate the spatial stacking pattern of graphene oxide and the interfacial architectures of graphene oxide and polyaniline.Flexible and sustainable sodium lignosulfonate-based electrodes are successfully developed,showing perfect bending stability and high electronic conductivity and specific capacitance(521 F·g^(−1)at 0.5 A·g^(−1)).Due to the resulting rational interfacial structure and stable ion-electron transport,the asymmetric supercapacitors provide a wide voltage window reaching 1.7 V,outstanding bending stability and high energy-power density of 83.87 Wh·kg^(−1)at 3.4 kW·kg^(−1).These properties are superior to other reported cases of asymmetric energy enrichment.The synergistic strategy of sodium lignosulfonate on graphene oxide and polyaniline is undoubtedly beneficial to advance the process for the construction of green flexible supercapacitors with remarkably wide voltage windows and excellent bending stability.

Recent progress of fiber-shaped batteries towards wearable application

Rapid development of portable or wearable devices, which is inspired by requirements of instant messaging,health monitoring and handling official business, urgently demands more tiny, flexible and light power sources. Fibershaped batteries explored in recent years become a prospective candidate to satisfy these demands. With 1D architecture,the fiber-shaped batteries could be adapted to various deformations and integrated into soft textile and other devices.Numerous researches have been reported and achieved huge promotion. To give an overview of fiber-shaped batteries,we summarized the development of fiber-shaped batteries in this review, and discussed the structure and materials in fiber-shaped batteries. The flexibility of batteries with the potential application of the batteries was also exhibited and showed the future perspective. Finally, challenges in this field were discussed, hoping to reveal research direction towards further development of fiber-shaped batteries.

Recent progress and future perspectives of flexible metal‐air batteries

With the rapid development of wearable and intelligent flexible electronic devices(FEDs),the demand for flexible energy storage/conversion devices(ESCDs)has also increased.Rechargeable flexible metal‐air batteries(MABs)are expected to be one of the most ideal ESCDs due to their high theoretical energy density,cost advantage,and strong deformation adaptability.With the improvement of the device design,material assemblies,and manufacturing technology,the research on the electrochemical performance of flexible MABs has made significant progress.However,achieving the high mechanical flexibility,high safety,and wearable comfortability required by FEDs while maintaining the high performance of flexible MABs are still a daunting challenge.In this review,flexible Zn‐air and Li‐air batteries are mainly exemplified to describe the most recent progress and challenges of flexible MABs.We start with an overview of the structure and configuration of the flexible MABs and discuss their impact on battery performance and function.Then it focuses on the research progress of flexible metal anodes,gel polymer electrolytes,and air cathodes.Finally,the main challenges and future research perspectives involving flexible MABs for FEDs are proposed.

Flexible electrical stimulation device with Chitosan-Vaseline®dressing accelerates wound healing in diabetes

The healing process of diabetic wounds is typically disordered and prolonged and requires both angiogenesis and epithelialization.Disruptions of the endogenous electric fields(EFs)may lead to disordered cell migration.Electrical stimulation(ES)that mimics endogenous EFs is a promising method in treating diabetic wounds;however,a microenvironment that facilitates cell migration and a convenient means that can be used to apply ES are also required.Chitosan-Vaseline■gauze(CVG)has been identified to facilitate wound healing;it also promotes moisture retention and immune regulation and has antibacterial activity.For this study,we created a wound dressing using CVG together with a flexible ES device and further evaluated its potential as a treatment for diabetic wounds.We found that high voltage monophasic pulsed current(HVMPC)promoted healing of diabetic wounds in vivo.In studies carried out in vitro,we found that HVMPC promoted the proliferation and migration of human umbilical vein endothelial cells(HUVECs)by activating PI3K/Akt and ERK1/2 signaling.Overall,we determined that the flexible ES-chitosan dressing may promoted healing of diabetic wounds by accelerating angiogenesis,enhancing epithelialization,and inhibiting scar formation.These findings provide support for the ongoing development of this multidisciplinary product for the care and treatment of diabetic wounds.

Materials and applications of bioresorbable electronics

Bioresorbable electronics is a new type of electronics technology that can potentially lead to biodegradable and dissolvable electronic devices to replace current built-to-last circuits predominantly used in implantable devices and consumer electronics. Such devices dissolve in an aqueous environment in time periods from seconds to months, and generate biological safe products. This paper reviews materials, fabrication techniques, and applications of bioresorbable electronics, and aims to inspire more revolutionary bioresorbable systems that can generate broader social and economic impact. Existing challenges and potential solutions in developing bioresorbable electronics have also been presented to arouse more joint research efforts in this field to build systematic technology framework.

Recent advances in fluorinated polymers:synthesis and diverse applications

Fluorinated polymers exhibit a unique combination of attributes,including chemical inertness,low surface energy,exceptional weather resistance,and intriguing electrical properties.This mini review provides an overview of recent advancements in the research of fluorinated polymers,highlighting the development of synthetic strategies for novel fluorinated polymers and their diverse applications in various fields.Traditional fluorinated polyolefins can be modified through chemical methods to produce functional materials.Copolymerization of fluorinated olefins with non-fluorinated monomers effectively addresses synthesis challenges,yielding main-chain fluoro-containing polymers with specific functional groups.Additionally,recent studies have revealed that free radical(co)polymerization of fluorinated(meth)acrylate monomers leads to new fluorinated polymers with enhanced solubility,processability,and structural diversity.Capitalizing on these new synthetic strategies,a range of fluorinated polymer materials has been developed for a multitude of applications,including flexible electrodes,alternating current(AC)electroluminescent devices,energy storage capacitors,triboelectric nanogenerators,and lithium batteries.With their customized structures and excellent properties,fluorinated polymers hold significant promise to uncover more potential applications in the era of flexible and wearable electronics.