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A supercapacitor is a potential electrochemical energy storage device with high‐power density (PD) for driving flexible, smart, electronic devices. In particular, flexible supercapacitors (FSCs) have reliable mechanical and electrochemical properties and have become an important part of wearable, smart, electronic devices. It is noteworthy that the flexible electrode, electrolyte, separator and current collector all play key roles in overall FSCs. In this review, the unique mechanical properties, structural designs and fabrication methods of each flexible component are systematically classified, summarized and discussed based on the recent progress of FSCs. Further, the practical applications of FSCs are delineated, and the opportunities and challenges of FSCs in wearable technologies are proposed. The development of high‐performance FSCs will greatly promote electricity storage toward more practical and widely varying fields. However, with the development of portable equipment, simple FSCs cannot satisfy the needs of integrated and intelligent flexible wearable devices for long durations. It is anticipated that the combining an FSC and a flexible power source such as flexible solar cells is an effective strategy to solve this problem. This review also includes some discussions of flexible self‐powered devices. In this review, the unique mechanical properties, structural designs, and fabrication methods of each flexible component are systematically classified, summarized, and discussed based on the recent progress of flexible supercapacitors (FSCs). Further, the practical applications of FSCs are delineated, and the opportunities and challenges of FSCs in wearable technologies are proposed.

Self‐healing soft electronic material composition is crucial to sustain the device long‐term durability. The fabrication of self‐healing soft electronics exposed to high moisture environment is a significant challenge that has yet to be fully achieved. This paper presents the novel concept of a water‐assisted room‐temperature autonomous self‐healing mechanism based on synergistically dynamic covalent Schiff‐based imine bonds with hydrogen bonds. The supramolecular water‐assisted self‐healing polymer (WASHP) films possess rapid self‐healing kinetic behavior and high stretchability due to a reversible dissociation–association process. In comparison with the pristine room‐temperature self‐healing polymer, the WASHP demonstrates favorable mechanical performance at room temperature and a short self‐healing time of 1 h; furthermore, it achieves a tensile strain of 9050%, self‐healing efficiency of 95%, and toughness of 144.2 MJ m−3. As a proof of concept, a versatile WASHP‐based light‐emitting touch‐responsive device (WASHP‐LETD) and perovskite quantum dot (PeQD)‐based white LED backlight are designed. The WASHP‐LETD has favorable mechanical deformation performance under pressure, bending, and strain, whereas the WASHP‐PeQDs exhibit outstanding long‐term stability even over a period exceeding one year in a boiling water environment. This paper provides a mechanically robust approach for producing eco‐friendly, economical, and waterproof e‐skin device components. This novel underwater self‐healing polymer, based on synergistically dynamic covalent Schiff‐based imine bonds with hydrogen bonds, is eco‐friendly, economical, waterproof, and resilient. It has outstanding performance in terms of stretchability (9050%), self‐healing efficiency (95%), self‐healing time (1 h at room temperature), and toughness (144.2 MJ m−3), giving it high potential for integration into underwater electronics.

As a new type of secondary ion battery, aqueous zinc‐ion battery has a broad application prospect in the field of large‐scale energy storage due to its characteristics of low cost, high safety, environmental friendliness, and high‐power density. In recent years, manganese dioxide (MnO2)‐based materials have been extensively explored as cathodes for Zn‐ion batteries. Based on the research experiences of our group in the field of aqueous zinc ion batteries and combining with the latest literature of system, we systematically summarize the research progress of Zn−MnO2 batteries. This article first reviews the current research progress and reaction mechanism of Zn−MnO2 batteries, and then respectively expounds the optimization of MnO2 cathode, Zn anodes, and diverse electrolytes and their effects on battery performance. Additionally, primary challenges related to different components and their respective strategies for mitigating them are discussed, with the ultimate objective of offering comprehensive guidance for the design and fabrication of high‐performance Zn−MnO2 batteries. Finally, the future research and development direction of aqueous Zn−MnO2 batteries with high energy density, high safety and long life is envisioned. In recent years, Zn−MnO2 batteries have attracted more and more attention. This review not only summarizes the battery mechanism under different pH, but also discusses the main challenges encountered and latest developments in anode and cathode materials and various electrolyte materials (liquid, solid and gel), which are crucial for enabling the design of high‐performance batteries. In the end, prospects of the sustainable development of Zn−MnO2 batteries are summarized.

In recent years, the proliferation of wearable healthcare devices has marked a revolutionary shift in the personal health monitoring and management paradigm. These devices, ranging from fitness trackers to advanced biosensors, have not only made healthcare more accessible, but have also transformed the way individuals engage with their health data. By continuously monitoring health signs, from physical-based to biochemical-based such as heart rate and blood glucose levels, wearable technology offers insights into human health, enabling a proactive rather than a reactive approach to healthcare. This shift towards personalized health monitoring empowers individuals with the knowledge and tools to make informed decisions about their lifestyle and medical care, potentially leading to the earlier detection of health issues and more tailored treatment plans. This review presents the fabrication methods of flexible wearable healthcare devices and their applications in medical care. The potential challenges and future prospectives are also discussed.

Carbon-based materials, including graphene, single walled carbon nanotubes (SWCNTs), and multi walled carbon nanotubes (MWCNTs), are very promising materials for developing future-generation electronic devices. Their efficient physical, chemical, and electrical properties, such as high conductivity, efficient thermal and electrochemical stability, and high specific surface area, enable them to fulfill the requirements of modern electronic industries. In this review article, we discuss the synthetic methods of different functionalized carbon materials based on graphene oxide (GO), SWCNTs, MWCNTs, carbon fibers (CFs), and activated carbon (AC). Furthermore, we highlight the recent developments and applications of functionalized carbon materials in energy storage devices (supercapacitors), inkjet printing appliances, self-powered automatic sensing devices (biosensors, gas sensors, pressure sensors), and stretchable/flexible wearable electronic devices.

Flexible strain sensors are essential components of wearable smart devices that perceive and respond to strain stimulations. However, the sensitivity and response time of most sensors require further improvement to detect subtle strains related to human bodies. Herein, an ultrasensitive flexible optical sensor with fast response time has been built based on a microfiber coupler encapsulated in polydimethylsiloxane. Benefiting from dramatic change of coupling ratio of the microfiber coupler under weak strain, this flexible strain sensor exhibits ultrahigh strain sensitivity (gauge factor, GF = 900), low detection limit (0.001%), ultrafast response time (<0.167 ms), wide sensing range (0.45%), and superior durability and stability (>10 000 cycles). Real‐time capturing and recognizing of respiration, broadband sound signals, and pulse waves at different sites of human body have been demonstrated based on this highly sensitive microfiber coupler sensor. Moreover, simultaneous detection of the wrist pulse and human voice has been achieved based on the frequency division multiplexing technology. This flexible photonics strain sensor could serve as the prototype of ultrasensitive flexible optical sensors with fast response time for the development of high performance and wearable healthcare devices. An ultrasensitive flexible optical sensor with fast response time is built based on a microfiber coupler encapsulated in polydimethylsiloxane. This flexible sensor realizes the monitoring of weak motion, sound signals, and pulse waves. The proposed flexible microfiber coupler sensor shows great potential for human–machine interfaces and soft robots.

Graphene composite yarns have demonstrated significant potential in the development of multifunctional wearable electronics, showcasing exceptional conductivity, mechanical properties, flexibility, and lightweight design. However, their performance is limited by the weak interfacial interaction between the fibers and graphene. Herein, a polydopamine–reduced graphene oxide (PDA–RGO) interfacial modulation strategy is proposed to prepare graphene-coated cotton yarns with high electrical conductivity and strength. PDA–RGO serves as an interfacial bonding molecule that interacts with the cotton yarn (CY) substrate to establish a hydrogen interface, while interconnecting with highly conductive graphene through π–π interactions. The developed interface-designed graphene-coated yarn demonstrates an impressive average electrical conductivity of (856.27 ± 7.02) S/m (i.e., average resistance of (57.57 ± 5.35) Ω). Simultaneously, the obtained conductive yarn demonstrates an exceptional average tensile strength of (172.03 ± 8.03) MPa, surpassing that of primitive CY by approximately 1.59 times. The conductive yarns can be further used as low-voltage flexible wearable heaters and high-sensitivity pressure sensors, thus showcasing their remarkable potential for high-performance and multifunctional wearable devices in real-world applications. Graphical Abstract

INTRODUCTION: Heart disease has been a major health challenge globally, therefore the development of reliable and real-time heart disease monitoring methods is crucial for the prevention and management of heart health. The aim of this study is to explore a flexible wearable device approach based on wavelet transform and support vector machine (SVM) to improve the accuracy and portability of heart disease monitoring. OBJECTIVES: The main objective of this study is to develop a wearable device that combines wavelet transform and SVM techniques to achieve accurate monitoring of physiological signals of heart diseases. METHODS: An integrated method for heart disease monitoring was constructed using flexible sensor technology combined with a wavelet transform and support vector machine. The Marr wavelet transform was applied to the ECG signals, and the feature vectors were constructed by feature parameter extraction. Then, the radial basis kernel SVM was utilized to identify the three ECG signals. The performance of the algorithm was optimized by adjusting the SVM parameters to improve the accurate monitoring of heart diseases. RESULTS: The experimental results show that the proposed wavelet transform and SVM-based approach for flexible wearable devices achieves satisfactory results in heart disease monitoring. In particular, the algorithm successfully extracted feature vectors and accurately classified different ECG signals by skillfully combining the wavelet transform and SVM techniques for the processing of premature beat signals. CONCLUSION: The potential application value of the wavelet transform and SVM-based flexible wearable device approach in heart disease monitoring is emphasized. By efficiently processing ECG signals, the method provides an innovative and comfortable solution for real-time monitoring of cardiac diseases.

Conventional methods of intestinal inspection play an essential role in the assessment of bowel diseases and other relevant health issues, yet fail to obtain intestinal conditions in real time because of radiation limits and operation inconvenience. Herein, a flexible, skin-mounted device is developed for long-term, real-time monitoring, and for the evaluation of bowel sounds based on the integration of a three-dimensional printed elastomeric resonator with flexible electronics. The device is capable of being flexibly attached to abdominal surfaces without performance degradation during breathing. Clinical tests conduct in a normal volunteer and in patients with mechanical intestinal obstruction or paralytic ileus illustrate the usefulness of the device in capturing the characteristics of bowel sounds. Furthermore, a demonstration of collection and classification of bowel sounds by the flexible device based on machine learning methods can serve as a reference for possible applications of the system in the auxiliary diagnosis of bowel problems.

The research interest in wearable sensors has tremendously increased in recent years. Amid the different biosensors, electrochemical biosensors are unparalleled and ideal for the design and manufacture of such flexible and wearable sensors because of their various benefits, including convenient operation, quick response, portability, and inherent miniaturization. A number of studies on flexible and wearable electrochemical biosensors have been reported in recent years for invasive/non-invasive and real-time monitoring of biologically relevant molecules such as glucose, lactate, dopamine, cortisol, and antigens. To attain this, novel two-dimensional nanomaterials and their hybrids, various substrates, and detection methods have been explored to fabricate flexible conductive platforms that can be used to develop flexible electrochemical biosensors. In particular, there are many advantages associated with the advent of two-dimensional materials, such as light weight, high stretchability, high performance, and excellent biocompatibility, which offer new opportunities to improve the performance of wearable electrochemical sensors. Therefore, it is urgently required to study wearable/flexible electrochemical biosensors based on two-dimensional nanomaterials for health care monitoring and clinical analysis. In this review, we described recently reported flexible electrochemical biosensors based on two-dimensional nanomaterials. We classified them into specific groups, including enzymatic/non-enzymatic biosensors and affinity biosensors (immunosensors), recent developments in flexible electrochemical immunosensors based on polymer and plastic substrates to monitor biologically relevant molecules. This review will discuss perspectives on flexible electrochemical biosensors based on two-dimensional materials for the clinical analysis and wearable biosensing devices, as well as the limitations and prospects of the these electrochemical flexible/wearable biosensors.Graphical abstract