Fibers and textiles with good flexibility, air permeability, and mechanical properties are indispensable materials in our daily lives. With the rapid development of flexible electronics, fabricating fibers and textiles that exhibit intelligent characteristics has become an attractive research topic. On the basis of the characteristics of common fibers or textiles, intelligent fibers and textiles may exhibit unique functions such as sensing, feedback, response, self-diagnosis, self-repair, and self-regulation. The development of intelligent fibers and textiles is closely related with the development of material science. Many materials, including metals, artificial polymers and natural biopolymers can be used for fabricating intelligent fibers and textiles. Compared with metals and artificial polymers, natural biopolymers have advantages of green source, biosafety, biodegradability and lightweight. Among natural biopolymers, natural silks, especially that from Bombyx mori, can be obtained in large amounts and have been used for clothes for thousands of years. Silkworm silk has exceptional mechanical properties, attractive luster, good biocompatibility and biodegradability. Therefore, silk materials are considered to be one of most promising candidates for intelligent fibers and textiles. In this review, we firstly introduce the hierarchical structures and basic properties of natural silk fibers. The exceptional mechanical properties of silk fibers can be ascribed to their unique hierarchical structures (from polypeptide chains, secondary structures to macroscopic fibers). The approaches to fabricate regenerated silk materials are briefly reviewed. The basic properties of silk materials, including the mechanical properties, biocompatibility, biodegradability, optical properties, piezoelectric properties, and thermal stability are presented. Then, the application of silk materials in various intelligent fibers and textiles, including fiber-based sensors, actuators, optical devices, energy harvesting and storage devices, are reviewed. Silk fibers can be functionalized and made into strain sensors, pressure sensors, and humidity sensors for applications in health monitoring. They can also transform into electrically conductive materials through high-temperature carbonization and then be fabricated into high-performance sensors or other functional devices. Silk-based actuators have been fabricated based on the response of silk to water or other molecules. Besides, silk-based fluorescence fibers and optical fibers were developed. Silk fibers have also been used in wearable energy devices by designing and fabricating piezoelectric nanogenerators, triboelectric nanogenerators, super-capacitors and batteries. The preparation methods, performance, and working mechanisms of those silk-based intelligent fibers and textiles are discussed in details. Finally, the persisting challenges and future opportunities of silk-based intelligent fibers and textiles are discussed. We believe that silk-based materials have great potential for intelligent fibers and textiles. The further development of this field will be accelerated by the continued development of material science and related techniques.

Graphene fiber, a macroscopic one-dimensional material formed by assembling elementary graphene flakes, has emerged in response to the increasing demand for multifunctional or even smart fibers. Based on the astonishing properties of graphene building blocks, graphene fiber presents a series of attractive features, such as superior mechanical strength and electronic conductivity, light-weight, and efficient thermal conductivity. As a result, graphene fiber exhibits broad prospects for application in ultralight cables for aerospace, wearable energy storage devices, biosensors, and neuroelectronics. graphene fiber may provide a critical breakthrough for realizing multi-functional fibers or even smart textiles. Since it was first prepared in 2011, numerous fabrication techniques have been developed to assemble graphene fiber, such as wet spinning, space-confined hydrothermal assembly, film twisting approaches, and template-assisted chemical vapor deposition. Among various graphene fiber preparation approaches, wet spinning has great application potential, as it affords the best mechanical strength and electrical conductivity of the prepared graphene fiber, along with great compatibility with the commercialized wet spinning technique. Therefore, the wet spinning approach has attracted extensive attention for batch production of high-performance graphene fiber. Herein, we introduce the pivotal steps of the wet spinning preparation of graphene fiber, with focus on summarizing the detailed strategies for enhancing the fiber properties and we also discuss the relationship between the structure and assembly approaches. The wet spinning technology for assembling graphene fiber includes a series of critical steps, such as preparation of the spinning liquid, bath coagulation, spinneret design, and post-treatment process. These procedures may have a significant influence on the micro-, meso-, and macro-structure of the final prepared graphene fiber. We also discuss the fundamental relationship between the typical properties of graphene fibers and their hierarchical structures, such as the in-planar structure of graphene sheets, aggregation structure of graphene flakes, and the macrostructure or morphology of graphene fiber. The recent advances in graphene fiber-based smart fibers and fabric applications are also analyzed, highlighting possible strategies for promoting structural-functional integrated applications. Finally, the current challenges and possible approaches for further improving the mechanical and electric properties of graphene fiber are presented. This review can be briefly divided into three parts: (1) details of the wet spinning process and its specific influence on the structural features of graphene fiber, (2) characteristics of current graphene fibers and promising strategies for enhancing the properties, (3) latest studies of graphene fiber applications and perspectives for future application.

Carbon nanotube fiber (CNTF) comprises continuous yarn-like macro aggregates with a large amount of carbon nanotubes and bundles thereof. CNTFs have excellent properties, such as high strength, toughness, and conductivity, because of which, they have broad prospects in several fields, such as structure-function integrated composite materials, fibrous energy devices, artificial muscle, and lightweight conductive wire. After two decades of development, breakthroughs have been made in continuous preparation technology, performance enhancement, and application exploration of CNTF materials. In this review, the development history of CNTF materials is summarized, and various continuous preparation technologies of CNTFs, including wet spinning, array spinning, and floating catalyst chemical vapor deposition (FCCVD) direct spinning, are described and compared. The wet spinning technology for fabricating CNTFs can be easily scaled due to its similarity to the conventional wet spinning technology used for fabricating high-performance fibers, while the obtained CNTFs have relatively high conductivity. The main challenges in wet spinning are the mass preparation and appropriate dispersion of high-quality carbon nanotubes (CNTs) with large aspect ratios. The array spinning technology can produce CNTFs with high purity and controllable structures, and its challenges are the relatively low preparation efficiency and high cost, because of which, it is challenging to meet the needs of large-scale applications. The FCCVD direct spinning technology can continuously produce CNTFs with relatively high strengths and at low cost, and it is easily adaptable for large-scale fabrication. The main drawbacks of CNTFs obtained from direct spinning are the relatively high impurity content and nonuniform CNT structures. Since CNTFs were first reported in 2000, one of the major challenges has been transferring the excellent properties of individual CNTs to the macroscopic assemblies of CNTs. To answer this question, the correlation between the structures and properties of CNTFs is discussed in detail, and contemporary techniques used for the enhancement of mechanical and electrical properties of CNTFs are reviewed. Based on the fiber fracture mechanism of slippage between CNTs, typical mechanical performance enhancement techniques include manipulating the CNT structures (namely wall number, diameter, aspect ratio, and collapse state), aligning the CNT along the fiber axis, enhancing the packing density and the interaction between CNTs, and combining with other reinforcing materials. The electrical performance of CNTFs is attributed to a 3D hopping electron transport mechanism in CNTFs. Conductivity enhancement techniques mainly include improving the assembly structure of CNTFs, using conductive materials as fillers between the CNTs, oxidative p-doping, and combining with metallic conductors. Finally, the main challenges in terms of performance enhancement and large-scale fabrication are discussed, and the development directions of CNTF materials are proposed.

The development of new types of artificial muscles is of utmost importance as traditional actuators based on mechanical drive systems no longer meet the stringent requirements of flexibility, high efficiency, and multi-stimuli responses in advanced functional fields, such as soft and biomimetic robots, sensors, artificial intelligent control, and artificial intelligence. Carbonene materials refer to carbon materials composed of all carbon atoms with sp² hybridization, mainly including carbon nanotubes and graphene. Owing to their exceptional properties such as light weight, excellent mechanical performance, high conductivity, flexibility, and large specific surface area, carbonene materials demonstrate significant application potential in artificial muscles, thereby promoting the rapid development of corresponding fields. Herein, the recent progress of the application of carbonene materials in artificial muscles is summarized to provide a comprehensive understanding of the preparation, properties, and applications of artificial muscles composed of carbonene materials. First, carbonene artificial muscles integrating response, actuation, and structure are introduced. As carbonene materials are unique building blocks that can be readily assembled into macroscopic materials with various structures, fibrous and membranous artificial muscles based on carbonene materials are discussed in detail. Carbonene fiber actuators demonstrate diverse actuation performances when fabricated with different structures. Bending actuation typically occurs when carbonene artificial muscles with asymmetric structures are subjected to external stimulation. The untwisting of carbonene artificial muscle fibers with twisted structures causes torsional and tensile actuation, which can be attributed to the volume expansion induced by external stimuli. Furthermore, coiled structures achieved by twisting a fiber until it is fully coiled can enhance the actuation stroke. Thus, the actuation of artificial muscle fibers made of carbonene materials can be classified into bending, rotation, and contraction actuations. Second, carbonene materials have long been considered as a functional component in composite materials for specific applications owing to their excellent physical and chemical properties. Therefore, the application of carbonene materials as an additional component to other artificial muscle materials (such as smart hydrogels, dielectric elastomers, and conducting polymers) is reviewed. By employing carbonene materials, artificial muscle materials exhibit improved electrical and mechanical properties, thereby leading to superior actuation performances. In addition, integrating carbonene materials into artificial muscles can endow the muscles with programmable actuation and sensing functions. Finally, the challenges faced in the application of artificial muscles based on carbonene materials and the future application of carbonene artificial muscles with multi-functional actuation performance are briefly discussed.

The development of high-performance polymer fibers is one of the main focus areas for the global polymer fiber industry. To ensure the advancement of important industries such as national aerospace, the performance of existing fibers should be improved, while new fibers that combine various properties and functions should also be developed. Carbonene materials, mainly comprising graphene and carbon nanotubes, exhibit excellent mechanical, electrical, thermal, and other properties; thus, they are considered ideal modifiers for high-performance polymer fibers. Herein, carbonene materials modified high-performance polymer fibers are reviewed to provide a comprehensive overview of their preparation, properties, and applications. Firstly, the preparation methods for these fibers, such as the dispersion of carbonene materials and polymer fiber modification methods, will be discussed. The dispersion methods employed for carbonene materials include mechanical mixing as well as covalent and non-covalent functionalization. Although mechanical mixing is relatively straightforward, functionalization typically provides better dispersion. To obtain well-dispersed carbonene materials, these methods should be combined. Polymer fiber modification methods include mixing, in situ polymerization, and coating. Although mixing can be performed during compounding of carbonene materials as well as a wide range of polymers, in situ polymerization generates stronger connections between carbonene materials and polymers, thus resulting in better properties compared to that obtained from mixing. Employing coating as a modification method offers the advantage of improving the surface properties as well as the possibility to introduce additional functionalities to the high-performance polymer fibers. Therefore, during preparation, the structure and function design of carbonene materials modified high-performance polymer fibers should be considered when the compounding method is selected. Subsequent discussions on the properties associated with these fibers will primarily focus on mechanical, electrical, and thermal properties. As carbonene materials can support loads and promote polymer crystallization and molecular chain orientation, it will contribute to improved mechanical properties. In addition, carbonene materials can develop conductive paths in the polymer fiber, thereby improving the electrical properties. These conductive networks further contribute to reducing segment motions in polymer molecular chains at a high temperature, thereby improving the thermal conductivity and thermostability of the materials. Through the addition of carbonene materials, new functions, such as UV resistance, resistance to photo-degradation, and improved surface affinity, can also be introduced. Finally, applications of carbonene materials modified high-performance polymer fibers will be addressed. These include potential applications as structural, heat-resistant, and wear-resistant materials that can be expected to exhibit superior performance when compared to conventional high-performance polymer fibers. Furthermore, additional functions that can be introduced to these modified fibers should make them ideally suited for applications in supercapacitors, sensors, electromagnetic shields, and artificial muscles. To conclude, existing challenges and potential future developments in carbonene materials modified high-performance polymer fibers will be discussed. The excellent properties associated with the modified fibers, as well as continuous development of materials and techniques should ensure their future applications in numerous fields.

Flexible and wearable electronics can integrate multiple functions, such as sensing, actuation, and wireless communication, showing great potential for application in flexible displays, health monitoring, human-computer interaction, and other fields. Energy devices to supply power are an important part of wearable electronics. Traditional energy devices have a relatively rigid plate structure, and their poor mechanical flexibility, low breathability and moisture conductivity make them difficult to adapt to the needs of wearability. These problems have severely limited the development and application of wearable devices, and there is therefore an urgent need to develop flexible, lightweight, high-performance wearable energy devices. Fiber-based energy devices have several obvious advantages. First, the diameter of these devices usually ranges from micrometers to millimeters, which makes them small in size and light in weight. Then, their outstanding flexibility endows them with wearable comfort and stable performance under mechanical deformation. Third, fibers can be woven or knitted into deformable textiles with excellent wearability and breathability. Because of these advantages, fiber-based energy devices have attracted considerable attention. Traditional fiber-based energy devices usually use polymer fibers covered by metal wires as electrodes, but these have inherent defects, such as poor chemical stability, inferior matching with active materials, and a lack of mechanical flexibility, that hinder their application in wearable devices. Carbonene materials are low-dimensional all-carbon materials composed of sp²-hybridized carbon atoms, including carbon nanotubes and graphene, which have the advantages of low density, good mechanical properties, excellent electrical and thermal conductivity, and high stability. "Carbonene fibers" mainly refers to high-performance fiber-like macroscopic assemblies composed of carbonene materials, and includes carbon nanotube fibers, graphene fibers, and graphene/carbon nanotube composite fibers. Carbonene fibers can effectively transfer the excellent performance of carbonene materials at the micro scale to the macro scale, showing high conductivity, strength, flexibility, stability, and ease of manufacture, making them widely used in research on advanced energy devices. In recent years, researchers have developed a variety of carbonene fiber-based energy devices. This paper reviews recent progress in the application of carbonene fibers in energy devices, including energy conversion and energy storage devices such as solar cells, moisture actuators and moisture power generators, thermoelectric generators, supercapacitors, and electrochemical cells. The preparation methods and wearable applications of carbonene fiber-based energy devices are emphasized. Discussion of the development prospects and challenges of energy storage/conversion devices based on carbonene fibers is included, and it is expected that this will provide valuable ideas for the future development of high-performance fiber-based wearable energy devices.

With the rapid advancement of intelligent microelectronics and the "Internet of Things" sensing microsystems with miniaturized and wearable properties, the development of novel fiber-based functional materials for application in flexible and microscale electrochemical energy storage devices has become an important strategic direction. However, this imparts higher requirements on the properties of fiber functional materials for use in flexible energy storage devices, including high bendability, stretchability, foldability, high strength, excellent interfacial stability, and high energy storage density. Based on its unique structure, excellent conductivity, and favorable mechanical and electrochemical properties, graphene-based fibers are expected to be a novel flexible functional material with high performance. To date, various strategies have been developed to control the microstructure to achieve further improvements in graphene fibers, from preparation methods to fundamental properties. In this review, a systematic summary of the recent advances in the preparation methods of graphene-based fibers is presented, including the limited hydrothermal synthesis, chemical vapor deposition (CVD), dry spinning, and wet spinning methods, and each method is discussed in terms of its advantages and disadvantages. Subsequently, strategies to improve the mechanical strength, electrical conductivity, and thermal conductivity of graphene fibers are highlighted, including the regulation of basic materials, improvement of the preparation process, and controlling subsequent processing. Recent research on the application of graphene fiber in energy storage and conversion is also summarized. Based on the exceptional electrical conductivity and pore structure of graphene fibers, it has significant application prospects in the field of electrochemical energy storage devices, such as supercapacitors, metal-ion batteries, and solar cells. Moreover, graphene fibers have a wide range of applications in phase change fibers and thermoelectric generators owing to their excellent thermal conductivity. This review summarizes and discusses the preparation of the basic constituent units of graphene fibers, development of novel graphene fibers, interfaces between graphene fibers and active materials, packaging strategies and safety issues of graphene fiber-based electrochemical energy storage devices, and current evaluation criteria for graphene fiber performance. Finally, the ongoing challenges and future prospects of graphene fibers for advanced energy conversion and storage systems are presented.

Technological advances such as electronic information and the Internet of Things have increased the daily use and demand for wearable electronic devices and intelligent fabrics. This has led to an unprecedented development of functional fibers, the properties of which are largely determined by their basic building blocks. Transitional metal carbon/nitrogen compounds (MXenes) are an emerging class of two-dimensional materials that have been widely used in many wearable devices owing to their high electrical conductivity, excellent processability, tunable surface properties, and outstanding mechanical strength. In this paper, we summarize the various synthetic methods for MXenes materials. Moreover, we also compare the characteristics of the different preparation techniques and elaborate the mechanical, electrical, optical, and chemical stability properties of the materials. This paper primarily focuses on the surface terminal groups of MXenes and the effect they have on different properties. At present, various methods have been developed for the preparation of MXenes-functionalized fibers, including pasting MXenes on the surface of matrix fibers by coating and producing solid fibers from a slurry containing MXenes by wet spinning or electrospinning. Among them, wet spinning has been the most widely adopted method, and is very promising for the large-scale production of MXenes-functionalized fibers. This paper also summarizes the properties of functional fibers obtained by various preparation methods. Furthermore, functional fibers prepared by different processes have been applied several fields, including flexible energy storage devices, wearable sensors, wires for electrical signal transmission and conversion, and integration of multifunctional intelligent fabrics. Great progress has been made in the research of supercapacitors and sensors with MXenes-functionalized fibers as electrodes which are anticipated to be integrated into intelligent textiles. This paper summarizes the potential applications of MXenes-functionalized fibers and reports on the challenges that must be addressed before practical applications can be realized. Firstly, a fluorine-free preparation of MXenes materials must be achieved whilst improving yields. Secondly, tunability of the functional groups on the surface of MXenes materials must be attained. Lastly, an improvement to the long-term chemical stability of MXenes in the environment should be accomplished. While efficiently obtaining high-quality MXenes materials, it is equally important to develop new MXenes-functionalized fiber preparation techniques. Furthermore, the potential applications of MXenes-functionalized fibers could be broadened by developing new fiber weaving processes. We finally summarize the potential applications of intelligent fabrics based on MXenes-functionalized fibers. Whilst challenges remain, MXenes are an emerging family of two-dimensional materials with many attractive properties and many potential applications worth exploring.

Natural spider silk is composed of spun spidroin protein containing beta-sheet crosslinking sites drawn from an S-shaped spinning duct. It exhibits an excellent combination of strength (1150 ± 200 MPa) and toughness (165 ± 30 MJ·m^–3) that originates from its hierarchical structure, including crosslinking sites, highly aligned nano-aggregates, and a sheath-core structure. In this work, we prepared a hydrogel fiber that contains crosslinking sites, highly aligned nano-aggregates, and a sheath-core structure, by draw-spinning a bulk hydrogel composed of polyacrylic acid crosslinked with vinyl-functionalized silica nanoparticles (SNVs). The core-sheath structure was prepared by the water-evaporation-controlled self-assembly of the polyacrylic hydrogel, while nanometer-sized aggregates were formed by the self-assembly of polyacrylic acid chains. The addition of a tiny amount of graphene oxide (GO: 0.01%), a 2D nanomaterial, enhanced the mechanical properties of the fiber (breaking strength: 560 MPa; fracture toughness: 200 MJ·m^–3; damping capacity: 94%). In addition, we investigated the factors responsible for the mechanical properties of the gel fibers, including fiber diameter, drying time in air, relative air humidity, and stretching speed. A higher breaking strength and a lower fracture strain was obtained by decreasing the fiber diameter, increasing the drying time, or increasing the stretching speed, while a lower fracture strain and higher breaking strength were obtained by increasing the relative air humidity. Polarized optical and SEM images revealed that the GO-seeded material is better aligned and contains smaller nano-aggregates, with GO seeding found to play a key role in the formation of nano-aggregates and polymer-chain alignment. The prepared fiber exhibited excellent mechanical properties compared to gel fibers prepared by other methods (e.g., electro-, wet, dry, and microfluidic spinning, as well as templating, and 3D printing, etc.). Repeated mechanical testing involving stretch-release cycles to 70% strain at 20% relative humidity revealed that the fibers have an energy-damping capacity of 93.6%, which exceeds that of natural spider silk and many types of artificial fiber. The relaxed stretched fiber recovered its initial length when exposed to 80% relative humidity, while the fiber recovered its initial mechanical properties when stored for 2 h at room temperature. A yarn composed of three hundred of the prepared gel fibers was shown to lift a 3 kg object without breaking; the prepared fiber was also shown to absorb dynamic energy and lower the impact force of a falling object.