Natural Biopolymers for Wearable Devices

The purpose of this study is to explore the main research hotspots in the design of wearable interactive devices and to explore the new trend of future development in light of the current research hotspots. The method is to use the information and literature on wearable interactive device design collected by Web of Science as the main data source, and use VOSviewer and CiteSpace to map the scientific knowledge of the literature, including the distribution of years and outputs, countries, research institutions, and keyword clustering, and then visualize and analyze them. The results show that the number of literature within the search range is on the rise overall, with China, the United States, and other countries in the leading position of research. The research hotspots mainly focus on the research of intelligent medical and human-computer interaction experience in wearable interaction systems, the research of intelligent device performance and core components, the research of material properties applicable to wearable devices, and the research of mechanical devices and functions in wearable device design. It is concluded that wearable interactive device design research has a strong interdisciplinary nature, and the future research focus will concentrate on the direction of intelligent interaction, user experience, sustainable material application, and device performance improvement of wearable devices. The future industry trend may be toward the direction of intelligent health detection, multi-device interconnection and interactive experience, sustainable and ecosystem integration, artificial intelligence analysis, cross-border integration, and innovation. Summarizing the current status and trends of research, we discuss the future development trend of wearable interactive device design from the strategy of natural interaction attributes of human-machine and human-ecology.

Low-cost, easy-to-deploy and self-driven flexible electronic devices and flexible sensors will bring new opportunities for developing the internet of things, wearable, and implantable technologies, especially human health monitoring, tactile perception and intelligent robot electronic skin. Therefore, it is necessary to provide high-performance and continuous energy supply modules for flexible electronic devices and flexible sensors. Nanogenerator can achieve high-performance sensing and energy storage characteristics by regulating the polarization electric field at the interface and surface, which is indeed an ideal adaptation choice. In particular, flexible piezoelectric nanogenerator can convert mechanical energy into electrical energy by piezoelectric properties, and can be applied to various deformation conditions such as bending, stretching and compression, which provides a novel solution to the problems of limited energy supply and insufficient performance in flexible electronic and self-driven technology. The piezoelectric output response of piezoelectric nanogenerator can be used not only as an energy signal to self-drive flexible electronic devices, but also as a sensing signal that can be integrated into the self-driven flexible sensors such as gas sensor, pressure sensor and biological sensor. Predictably, self-powered gas sensor with energy harvesting and high-sensitivity sensing, and self-charging power cell with energy harvesting and efficient storage will become hot topics. In this paper, we review the recent developments of flexible piezoelectric nanogenerators in flexible sensors and energy storage devices.

With the continuous development of wearable electronics, flexible energy storage devices have received widespread attention. Aqueous magnesium-ion supercapacitors (MSCs) have attracted great attention due to their high safety and low cost. However, the freeze of aqueous electrolytes will lead to rapid deterioration of aqueous MSCs performances, which hinders their application in wearable electronics. Herein, we propose a water-sulfolane hybrid electrolyte based on low-concentration Mg(ClO4)2 and sulfolane exhibiting excellent low-temperature properties. By investigating the physical characterization and electrochemical performance testing of the hybrid electrolyte revealed that sulfolane contains functional groups disrupting the hydrogen-bond network between water molecules, resulting in superior anti-freezing properties. The hybrid electrolytes endow flexible aqueous MSCs with a wider temperature operating range (-50 °C~25 °C), high specific capacitance of 22 F/g at -30 °C, and superior flexibility. This work provides an effective and feasible strategy for flexible energy storage systems operating in ultra-low temperatures environments.

With the rapid development of portable and wearable electronics, flexible fiber‐shaped energy storage devices have emerged as important solutions due to their lightweight nature, long cycle life, and high safety. High‐performance electrode materials are key to enhancing electrochemical performance. Carbon nanotubes (CNTs), with their 1D nanostructure, excellent mechanical properties, and ultra‐high tensile strength, are considered ideal for constructing flexible energy storage electrodes, particularly in applications balancing flexibility and electrochemical performance. Recent years have seen significant progress in CNT‐based flexible electrode research. To meet the demand for high‐capacity flexible energy storage, this review focuses on CNT‐based fiber‐shaped devices, which exhibit high capacity and excellent mechanical flexibility. It summarizes recent advancements in energy storage, emphasizing fabrication and modification techniques for fiber electrodes and strategies for improved flexibility and stretchability. Furthermore, the structural design and performance of devices based on preparation methods are elaborated in detail, alongside a discussion of their wearable application potential. This review also addresses core challenges in the field and outlines future research directions for advancing fiber‐shaped energy storage devices.

Emerging classes of soft robotics with flexible actuation, intelligent sensibility, and biomimetic functionality are driving significant advances in academic researches and commercial applications. Such new generation robotics relies heavily on important breakthroughs in soft matter engineering and flexible actuation systems. Unlike conventional rigid robots, soft robots generally have unique sporting styles and manufacturing strategies. Recently, a series of newly developed soft materials—gallium‐based liquid metals (LMs) are found to display dramatical roles in making soft machines and robotics with their unusual properties in soft robotic actuation and self‐driven field. With superior merits of both high stretchability and electroconductivity over conventional soft materials, LM is increasingly innovated as flexible sensors and actuators in constructing intelligent soft robots. Typical advances in LM enabled soft machines and robotics are summarized and interpreted, herein, with special focus on the driving principles of the LM objects, the preparation methods of LM flexible electronics for making soft robots, and the applications of LM in biomedicines and intelligent robots, together with the consideration of key challenges facing LM‐based soft robotics and its future prospects.

Chapter 3 - Chitin and chitosan composites for wearable electronics and energy storage devices

• Innovative fabrication method The study introduces a novel approach for fabricating flexible, freestanding UV sensors using additive manufacturing, specifically Direct Ink Writing (DIW), integrating tetrapodal zinc oxide (t-ZnO) particles and carbon nanotubes (CNTs) in a polyvinyl butyral (PVB) matrix. • Laser milling for functionality A selective laser milling process is employed to expose the semi-embedded t-ZnO particles, enabling effective UV sensing while preserving the flexibility and structural integrity of the printed sensor. • Enhanced adaptability The flexible sensors can be attached to a wide variety of surfaces and surface geometries, enabling potential applications in wearable electronics, soft robotics, and the Internet of Things (IoT). • Robust mechanical performance The sensor demonstrates robust mechanical stability, retaining its UV sensing capabilities under cyclic stretching and compression, with only minor current fluctuations, indicating excellent structural integrity of the particle network and polymer matrix. The fabrication of microelectronics via additive manufacturing holds previously inaccessible potential compared to cleanroom-based technologies. Printing electronics is comparably simple and cost-efficient. The main advantage, however, lies in the choice of materials. While cleanroom-based fabrication always has a two-dimensional topology, printed electronics can involve inherently complex-shaped micro- and nanoparticles with outstanding functionalities. This work reports on an approach for the assembly of flexible, ultraviolet light (UV) sensors involving complex-shaped tetrapodal zinc oxide (t-ZnO) particles and carbon nanotubes via direct ink writing (DIW). The morphology of these particles eliminates the need for traditional methods of processing; instead, they can be processed through printing a particle-laden polymer solution. This approach enables to shape the functional t-ZnO particles in a facile and fast manner. A subsequent laser milling process removes the binder polymer from the top layers and exposes the semi-embedded particles, effectively forming a UV sensor. This sensor then exhibits a UV responsivity of 0.29 ± 0.01 µA/(W/cm 2 ) and an UV on off current ratio of over 500 in a span of 10 s while maintaining the flexibility of the binder polymer. This flexibility also allows the attachment of the sensor to a great variety of surfaces and surface geometries and facilitates the formation of free-standing structures. The sensors flexibility and I on /I off ratios are maintained up to a bending radius of 5 mm and also under cyclic mechanical deformation, which tested up to 1000 cycles.

A semi-interpenetrating network ionic composite hydrogel with low modulus, fast self-recoverability and high conductivity as flexible sensor

Synchronous-ultrahigh conductive-reactive N-atoms doping strategy of carbon nanofibers networks for high‐performance flexible energy storage

Ti3C2Tx/g-C3N4 heterostructure films with outstanding capacitance for flexible Solid-state supercapacitors

Hierarchical core-shell polypyrrole@NiCo layered double hydroxide arrays grown on stainless steel yarn with high flexibility for 1D symmetric yarn-shaped supercapacitors

Elastic Cu@PPy sponge for hybrid device with energy conversion and storage

Over the past decade, two-dimensional (2D) Ti3C2T x MXenes demonstrated attractive characteristics such as high electrical conductivity, tunable layered structure, controllable interfacial chemical composition, high optical transparency, and excellent electromagnetic wave absorption, enabling Ti3C2T x MXenes as promising electrode materials in energy storage devices. Among these devices, flexible energy storage devices have attracted wide attention and developed rapidly due to the synchronously excellent electrochemical and mechanical properties. This review summarizes the recent progress of Ti3C2T x MXenes pertaining to novel material preparation and promising applications in energy storage and conversion including batteries, supercapacitors, solar cells, and solar steam generation. This work aims to provide an in-depth and reasonable understanding of the relationship between the unique nanostructure/chemical composition of Ti3C2T x MXenes and competitive electrochemical properties, which will facilitate the development of 2D Ti3C2T x MXenes for practical energy storage and solar energy conversion devices.

Porous cellulose/graphene oxide nanocomposite as flexible and renewable electrode material for supercapacitor

With advances in new materials and technologies, there has been increasing research focused on flexible sensors. However, in most flexible pressure sensors made using new materials, it is challenging to achieve high detection sensitivity across a wide pressure range. Although traditional silicon-based sensors have good performance, they are not formable and, because of their rigidity and brittleness, they are not suitable for fitting with soft human skin, which limits their application in wearable devices to collect various signals. Silicon nanomembranes are ultra-thin, flexible materials with excellent piezoresistive properties, and they can be applied in various fields, such as in soft robots and flexible devices. In this study, we developed a flexible pressure sensor based on the use of silicon nanomembranes (with a thickness of only 340 nm) as piezoresistive units, which were transferred onto a flexible polydimethylsiloxane (PDMS) substrate. The flexible pressure sensor operated normally in the range of 0-200 kPa, and the sensitivity of the sensor reached 0.0185 kPa-1 in the low-pressure range of 0-5 kPa. In the high-pressure range of 5-200 kPa, the sensitivity of the sensor was maintained at 0.0023 kPa-1. The proposed sensor exhibited a fast response and excellent long-term stability and could recognize human movements, such as the bending of fingers and wrist joints, while maintaining a stable output. Thus, the developed flexible pressure sensor has promising applications in body monitoring and wearable devices.