Carbon Nanotube Yarn for Fiber-Shaped Electrical Sensors, Actuators, and Energy Storage for Smart Systems

Bionic learning in MXene-based actuators: An emerging frontier

Bionics offers valuable insights into the design and application of MXene-based soft actuators, which have garnered significant attention in the fields of flexible electronics and smart materials owing to their exceptional electrical conductivity, tunable interlayer spacing, and responsiveness to diverse external stimuli. This review begins with a comprehensive summary of the main response mechanisms of MXene-based soft actuators under various external stimuli. It presents a detailed analysis of the advantages and limitations of different actuation modes and discusses strategies for composite modification with other materials to enhance MXene performance under multi-stimulus conditions. Inspired by the sensory capabilities of animals and plants in nature, this work explores the potential for biomimetic design and identifies four key challenges for advancing the field: (1) the development of efficient and controllable material synthesis techniques, (2) the electrochemical stability and environmental robustness of devices, (3) the overall performance optimization of actuators, and (4) the nascent exploration of biomimetic learning mechanisms. Finally, future research directions are outlined, offering novel perspectives to promote the broader application of MXene-based soft actuators in biomimetic systems.

Adaptive Smart Materials in Architecture: Enhancing Durability and Sustainability in Modern Construction

Adaptive materials in civil construction offer superior performance and high potential for 4D printing integration. Smart materials exhibit rapid response times, precise sensor applications, and real-time durability monitoring, with phase-changing materials improving thermal efficiency by 30% and self-sensing concrete detecting microstrains as low as 10 με. These materials enhance fracture toughness (50% increase), corrosion resistance (40% improvement), and fire stability (up to 1200 °C). Smart bricks incorporate phase-change materials, glazing systems, and recyclable composites, with some embedding electrodes achieving conductivity of 10-3 S/m for strain sensing. Additive manufacturing (AM) reduces material waste by 50%, enhances design flexibility (90%), and lowers the carbon footprint (40-60%). This review examines communication protocols such as Zigbee, LoRaWAN, and 5G, which enable real-time data transfer and processing. However, embedded systems in smart bricks may be vulnerable to cyber-attacks and data breaches. Ensuring security involves encryption methods, blockchain technology, intrusion detection systems to protect data integrity and network reliability, 3D-printed smart bricks, categorizing materials, and fabrication mechanisms. Integrating AM with smart materials fosters resilient, energy-efficient construction, essential for sustainable urbanization.

Clustered Carbon Nanotubes Damage Endoplasmic Reticulum

Carbon nanotubes (CNTs) have garnered significant attention in recent years due to their unique properties and their wide-range applicability. However, alongside these promising applications, concerns regarding the potential toxicity of CNTs have emerged. In this context, through this work, we have attempted to explore the nanotoxic effect of CNTs over endoplasmic reticular (ER). Using structure illumination and transmission electron microscopies, we unveiled that during endocytosis processes, CNTs form clusters, which lead to fragmentation of the ER structure by puncturing them, thereby inducing potential nanotoxicity. In addition, RNA sequencing data showed that after incubation with CNTs, activating transcription factor 4 (ATF4), a gene responsible for ER stress, was found to be up-regulated. To explore the molecular mechanism, we employed molecular dynamics and coarse-grained simulations and found that clustering of CNTs can significantly increase the speed of lipid extraction, resulting in severe damage.

Hierarchically Porous Wearable Composites for High-Performance Stretchable Supercapacitors

With the rapid development of wearable electronic devices, the demand for flexible, durable, and high-performance energy storage systems has increased significantly. Nevertheless, maintaining stable electrochemical performance during stretching while ensuring high stretchability and mechanical stability remains a challenge. Herein, this study proposes a novel type of stretchable supercapacitors made from carbon nanotube (CNT) and styrene-butadiene-styrene (SBS) composite scaffolds prepared on pre-stretched carbon fabrics using the breath figure method. Hydrothermal treatment is then performed to grow NiCo-LDH at the treated carbon fabrics. This method induces the formation of a hierarchically porous structure under high humidity conditions, controls the hydrothermal growth of NiCo-LDH in the CNT/SBS composite scaffold, and significantly enhances the electrochemical performance and mechanical stability. The supercapacitor demonstrates remarkable retention of 94% capacitance under 80% tensile strain and sustains a small 8% degradation over 20 000 charge-discharge cycles, achieving a specific capacitance of 4948 mF cm⁻2 at 2 mA cm⁻2. The device has an energy density of 801.6 µWh cm⁻2 (400.6 Wh kg⁻¹) and exhibits excellent performance at a power density of 3.5 mW cm⁻2 (1749.5 W kg⁻¹). These properties make the supercapacitors a potential for next-generation smart wearables and wearable electronics.

Rapid and simple on-site salmonella detection in food via direct sample loading using a lipopolysaccharide-imprinted polymer

Salmonella is a major foodborne pathogen that causes salmonellosis, which is characterized by symptoms such as diarrhea, fever, and abdominal cramps. Existing methods for detecting Salmonella, such as culture plating, ELISA, and PCR, are accurate but time-consuming and unsuitable for on-site applications. In this study, we developed a rapid and sensitive electrochemical sensor using a molecularly imprinted polymer (MIP) to detect Salmonella typhimurium (S. typhimurium) by targeting lipopolysaccharides (LPS). Polydopamine (PDA) was used as the polymer matrix because of its cost-efficiency and functional versatility. The sensor demonstrated high sensitivity and selectivity, with a detection limit of 10 CFU/mL and a linear response over the 10²-10⁸ CFU/mL range. The specificity of the sensor was validated against other gram-positive and gram-negative bacteria and showed no significant cross-reactivity. Furthermore, the sensor performed effectively in real food samples, including tap water, milk, and pork, without complex preprocessing. These results highlight the potential of the LPS-imprinted MIP sensor for practical on-site detection of S. typhimurium, improving food safety monitoring and preventing outbreaks in food-handling environments.

Versatile and Fast Electrochemical Activation Method for Carbon Nanotube Fibers with Diverse Active Materials

In this study, the challenge of non-electrochemical activity in carbon nanotube fibers (CNTFs) is addressed by developing a modified chlorosulfonic acid (CSA) densification process specifically developed for directly spun CNTFs. This post-treatment method, well-known for enhancing the physical properties of CNTFs, utilizes the double diffusion phenomenon to efficiently integrate a diverse range of active materials, from conductive polymers like polyaniline (PANI) to metal oxides like nickel oxide (NiO), into the fibers. This universal and cost-effective approach not only simplifies the integration process but also significantly boosts both the electrochemical and physical properties of the fibers. For instance, the PANI@CNTF composite exhibited a remarkable 17-fold increase in specific capacitance and a two-fold increase in load value compared to its pristine counterparts. This method proves straightforward, efficient, and versatile, making it suitable for developing fiber-shaped electrodes that advance the capabilities of wearable energy storage systems.

Exploring Pyrazine-Based Organic Redox Couples for Enhanced Thermoelectric Performance in Wearable Energy Harvesters

Thermoelectric generators (TEGs) based on thermogalvanic cells can convert low-temperature waste heat into electricity. Organic redox couples are well-suited for wearable devices due to their nontoxicity and the potential to enhance the ionic Seebeck coefficient through functional-group modifications.  Pyrazine-based organic redox couples with different functional groups is comparatively analyzed through cyclic voltammetry under varying temperatures. The results reveal substantial differences in entropy changes with temperature and highlight 2,5-pyrazinedicarboxylic acid dihydrate (PDCA) as the optimal candidate. How the functional groups of the pyrazine compounds impact the ionic Seebeck coefficient is examined, by calculating the electrostatic potential based on density functional theory. To evaluate the thermoelectric properties, PDCA is integrated in different concentrations into a double-network hydrogel comprising poly(vinyl alcohol) and polyacrylamide. The resulting champion device exhibits an impressive ionic Seebeck coefficient (Si) of 2.99 mV K-1, with ionic and thermal conductivities of ≈67.6 µS cm-1 and ≈0.49 W m-1 K-1, respectively. Finally, a TEG is constructed by connecting 36 pieces of 20 × 10-3 m PDCA-soaked hydrogel in series. It achieves a maximum power output of ≈0.28 µW under a temperature gradient of 28.3 °C and can power a small light-emitting diode. These findings highlight the significant potential of TEGs for wearable devices.

Recent Progress in Polymer Gel-Based Ionic Thermoelectric Devices: Materials, Methods, and Perspectives

Polymer gel-based ionic thermoelectric (i-TE) devices, including thermally chargeable capacitors and thermogalvanic cells, represent an innovative approach to sustainable energy harvesting by converting waste heat into electricity. This review provides a comprehensive overview of recent advancements in gel-based i-TE materials, focusing on their ionic Seebeck coefficients, the mechanisms underlying the thermodiffusion and thermogalvanic effects, and the various strategies employed to enhance their performance. Gel-based i-TE materials show great promise due to their flexibility, low cost, and suitability for flexible and wearable devices. However, challenges such as improving the ionic conductivity and stability of redox couples remain. Future directions include enhancing the efficiency of ionic-electronic coupling and developing more robust electrode materials to optimize the energy conversion efficiency in real-world applications.

Multilayer Core-Sheath Structured Nickel Wire/Copper Oxide/Cobalt Oxide Composite for Highly Sensitive Non-Enzymatic Glucose Sensor

The development of micro glucose sensors plays a vital role in the management and monitoring of diabetes, facilitating real-time tracking of blood glucose levels. In this paper, we developed a three-layer core-sheath microwire (NW@CuO@Co3O4) with nickel wire as the core and copper oxide and cobalt oxide nanowires as the sheath. The unique core-sheath structure of microwire enables it to have both good conductivity and excellent electrochemical catalytic activity when used as an electrode for glucose detecting. The non-enzymatic glucose sensor base on a NW@CuO@Co3O4 core-sheath wire exhibits a high sensitivity of 4053.1 μA mM-1 cm-2, a low detection limit 0.89 μM, and a short response time of less than 2 s.

Humidity-responsive fiber actuators assembled from cellulose nanofibrils

Fiber actuators, particularly valuable in soft robotics and environmental sensing, are at the forefront of "smart" materials and materials innovation. In this realm, torsional and tensile biofiber actuators, notable for their cost-effectiveness and biodegradability, mark a critical gap in the development of next-generation functional systems and devices. To address this gap, this study showcased moisture-responsive fiber actuators made from cellulose nanofibrils (CNFs). The initial focus of this contribution was on an innovative torsional actuator, which capitalized on the hydrophilic nature of the CNFs filaments produced through wet-spinning processes. These robust filaments, with a mechanical strength of (237.0 ± 10.7) MPa, were twisted to form the torsional actuator. This actuator demonstrated a rapid rotational response, achieving up to 1180 rpm within merely 10 s of exposure to moisture, and maintained high durability over multiple cycles. Building upon this platform, the study continued and aimed to build up a tensile actuator, which ingeniously integrated a supercoiled nylon fiber core within a moisture-sensitive CNFs sheath. This design enhances the structural support and functionality of the actuator. The pursued transition from torsional to tensile actuator demonstrates an iterative and innovative approach in actuator technology, underscoring the versatility and potential of CNFs in the realm of "smart" actuation materials.

Hybrid Materials Based on Carbon Nanotubes and Tetra- and Octa-Halogen-Substituted Zinc Phthalocyanines: Sensor Response Toward Ammonia from the Quantum-Chemical Point of View

This paper presents the results of quantum-chemical modeling performed by the Density Functional-Based Tight Binding (DFTB) method to investigate the change in the band structure of hybrid materials based on carbon nanotubes and unsubstituted, tetra-, or octa-halogen-substituted zinc phthalocyanines upon the adsorption of ammonia molecules. The study showed that the electrical conductivity of these materials and its changes in the case of interaction with ammonia molecules depend on the position of the impurity band formed by the orbitals of macrocycle atoms relative to the forbidden energy gap of the hybrids. The sensor response of the hybrids containing halogenated phthalocyanines was lower by one or two orders of magnitude, depending on the number of substituents, compared to the hybrid with unsubstituted zinc phthalocyanine. This result was obtained by calculations performed using the nonequilibrium Green's functions (NEGF) method, which demonstrated a change in the electrical conductivity of the hybrids upon the adsorption of ammonia molecules. The analysis showed that in order to improve the sensor characteristics of CNT-based hybrid materials, preference should be given to those phthalocyanines in which substituents contribute to an increase in HOMO energy relative to the unsubstituted macrocycles.

Bioinspired Mechanochromic Liquid Crystal Materials: From Fundamentals to Functionalities and Applications

Inspired by intriguing color changeable ability of natural animals, the design and fabrication of artificial mechanochromic materials capable of changing colors upon stretching or pressing have attracted intense scientific interest. Liquid crystal (LC) is a self-organized soft matter with anisotropic molecular alignment. Due to the sensitivity to various external stimulations, LC has been considered as an emerging and appealing responsive building block to construct intelligent materials and advanced devices. Recently, mechanochromic LC materials have becoming a hot topic in multifields from flexible artificial skins to visualized sensors and smart biomimetic devices. In this review, the recent progress of mechanochromic LCs is comprehensively summarized. Firstly, the mechanism and functionalities of mechanochromic LC is introduced, followed by preparation of various functional materials based on mechanochromic LCs. Then the applications of mechanochromic LCs are provided. Finally, the conclusion and outlooks of this field is given. This overview is hoped to provide inspiration in fabrication of advanced functional soft materials for scientists and engineers from multidisciplines including materials science, elastomers, chemistry, and physical science.

Capillary filling dynamics in closed-end carbon nanotubes-Defying the classical Lucas-Washburn paradigm

The emergence of two-dimensional (2D) materials such as carbon nanotubes (CNTs) offers the possibility of exploring new regimes of capillarity and wetting that remained inaccessible with traditional microfluidic and nanofluidic substrates. Here, we bring out the non-intuitive capillary filling regimes in closed-end CNTs using molecular-level investigations. Contrary to the existing understanding of the advancing liquid meniscus getting retarded by the viscous resistance offered by an entrapped vapor phase in a three-dimensional capillary, here the liquid meniscus is shown to accelerate toward the later stages of the dynamic wetting, which is attributed to the modified surface friction due to a 2D interface. This apparently counterintuitive observation is qualitatively linked to the local pressure fluctuations across the meniscus caused by the spontaneous bombardment of the entrapped vapor molecules, which may ramify into hitherto unexplored phenomena of a shape-reversed meniscus advancing in the 2-D pore. We further develop a simple analytical model to represent the essential physics of the resulting capillary filling dynamics, featuring significant deviations from the classical Lucas-Washburn paradigm. These results may turn out to be imperative in realizing new regimes of capillarity in 2D materials in multifarious applications, ranging from energy storage and water filtration to thin film flows in integrated electronics and photonic devices.

High Mobility, Low Off-Current, and Flexible Fiber-Based a-InGaZnO Thin-Film Transistors toward Wearable Textile OLED Displays

Fiber-based organic light-emitting diodes (OLEDs) are gaining attention as promising candidates to achieve truly wearable textile displays because of their favorable electrical and mechanical characteristics. However, although fiber OLEDs have been developed into passive-matrix displays, it has not been possible to achieve active OLED operation because of the difficulty of realizing fiber-based thin film transistors (TFTs) with the proper electrical and mechanical performance at the same time. Here, 1D cylindrical fiber-based IGZO TFTs, which simultaneously exhibit a high electrical performance and flexibility, are reported. To address this trade-off relationship, four key stages of a novel fabrication process and unique device structures that suitable for the thermal properties and cylindrical structure of the fiber were applied: (I) prethermal treatment, (II) partially patterned layers, (III) coplanar structure, and (IV) continuous postannealing (CPA) process. As a result, the fabricated fiber-based IGZO TFTs showed high mobility (8.6 cm2/(V s)) and low off-current (∼10-12 A), comparable to that glass-based TFTs, as well as flexibility. Furthermore, based on these valid performances, it was demonstrated that fiber phOLEDs could be driven by fiber-based IGZO TFTs using a wiring connection with Cu wire and Ag paste. The results suggest that this may allow the potential fabrication of fully textile AMOLED displays, integrated with TFTs.

Reversible Electrochemical Swelling of Straight Carbon Nanotube Yarns for High-Performance Linear Actuation

Coiled artificial muscle yarns outperform their straight counterparts in contractile strokes. However, challenges persist in the fabrication complexity and the susceptibility of the coiled yarns to becoming stuck by surrounding objects during contraction and recovery. Additionally, torsional stability remains a concern. In this study, it is reported that straight carbon nanotube (CNT) yarns when driven by a low-voltage electrochemical approach, can achieve a contractile stroke that surpasses even NiTi shape memory alloy fibers. The key lies in the suitable match between a yarn consisting of randomly aligned CNTs and the reversible and substantial electrochemical swelling induced by solvated ions. Wrinkled structures are formed on the surface of the CNT yarn to adapt to the swelling process. This not only assures torsional stability but also enhances the surface area for improved electrode-electrolyte interaction during electrochemical actuation. Remarkably, the CNT artificial muscle yarn generates a contractile stroke of 8.8% and an isometric stress of 7.5 MPa under 2.5 V actuation voltages, demonstrating its potential for applications requiring low energy consumption while maintaining high operational efficiency. This study highlights the crucial impact of CNT orientation on the effectiveness of electrochemically-driven artificial muscles, signaling new possibilities in smart material and biomechanical system development.

Control of myotube orientation using ultrasonication

This study investigated a technique for controlling the orientation of C2C12-derived myotube cells using ultrasonication for future clinical applications of cultured skeletal muscle tissues. An ultrasonicating cell culture dish, comprising a plastic-bottomed culture dish and a circular glass plate (diameter, 35 mm; thickness, 1.1 mm) attached to an annular piezoelectric ultrasonic transducer (inner diameter, 10 mm; outer diameter, 20 mm; thickness, 1 mm), was constructed. A concentric resonant vibrational mode at 89 kHz was generated on the bottom of the dish, and the orientations of myotube cells were quantitatively evaluated using two-dimensional Fourier transform analysis of phase contrast microscopy images captured over a 14 × 10 mm2 area at the center of the dish. Unsonicated myotube cells grew in random directions, but ultrasonication aligned them circumferentially in the culture dish. The timing of treatment was important, with ultrasonication for 48 h before differentiation having a greater impact on myotube orientation than ultrasonication after differentiation. A larger ultrasonic vibration, with an amplitude of over 20 Vpp, resulted in significantly smaller angles of deviation in the circumferential direction than the control. Ultrasonication enhanced the expression of differentiation-related genes and the formation of aligned myotubes, suggesting that it promotes differentiation of C2C12 cells into myotubes.

Fast Responsive and High-Strain Electro-Ionic Soft Actuator Based on the 3D-Structure MXene-EGaIn/MXene Bilayer Composite Electrode

Electro-ionic soft actuators have garnered significant attention owing to their promising applications in flexible electronics, wearable devices, and soft robotics. However, achieving high actuation performance (large bending strain and fast response time) of these soft actuators under low voltage has been challenging due to issues related to ion diffusion and accumulation. In this study, an electro-ionic soft actuator is fabricated using Ti3C2Tx MXene and eutectic gallium-indium (EGaIn) composite material as the bilayer electrode and methylammonium formate/1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride) (MAF-EMIMBF4/PVDF) as the ionic liquid-type electrolyte. The research results indicate that the prepared soft actuator exhibits excellent actuation performance with a peak-to-peak displacement of 35 mm and a bending strain of 0.69% (a peak-to-peak strain of 1.38%) under a low voltage (3 V). The electro-ionic soft actuator shows a wide frequency range (0.1-10 Hz), fast response time (0.35 s), and a rise time of 7.5 s. Furthermore, it demonstrates good cyclic durability, with a retention rate of 92.5% of its performance for 10 000 cycles. These excellent performances are attributed to the 3D structure of the Ti3C2Tx-EGaIn/Ti3C2Tx bilayer composite electrode, as well as the characteristics of the low viscosity, high conductivity, small ion volume, and larger volume difference between cations and anions in MAF ionic liquid. The high-performance electro-ionic soft actuator can be used in various fields such as artificial muscles, tactile devices, and soft robots.

N-DMBI Doping of Carbon Nanotube Yarns for Achieving High n-Type Thermoelectric Power Factor and Figure of Merit

The application of carbon nanotube (CNT) yarns as thermoelectric materials for harvesting energy from low-grade waste heat including that generated by the human body, is attracting considerable attention. However, the lack of efficient n-type CNT yarns hinders their practical implementation in thermoelectric devices. This study reports efficient n-doping of CNT yarns, employing 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzimidazole-2-yl) phenyl) dimethylamine (N-DMBI) in alternative to conventional n-dopants, with o-dichlorobenzene emerging as the optimal solvent. The small molecular size of N-DMBI enables highly efficient doping within a remarkably short duration (10 s) while ensuring prolonged stability in air and at high temperature (150 °C). Furthermore, Joule annealing of the yarns significantly improves the n-doping efficiency. Consequently, thermoelectric power factors (PFs) of 2800, 2390, and 1534 µW m-1 K-2 are achieved at 200, 150, and 30 °C, respectively. The intercalation of N-DMBI molecules significantly suppresses the thermal conductivity, resulting in the high figure of merit (ZT) of 1.69×10-2 at 100 °C. Additionally, a π-type thermoelectric module is successfully demonstrated incorporating both p- and n-doped CNT yarns. This study offers an efficient doping strategy for achieving CNT yarns with high thermoelectric performance, contributing to the realization of lightweight and mechanically flexible CNT-based thermoelectric devices.

Effect of Thermal Oxidation of Carbon Nanotubes during Wet Spinning into Fibers Using Sodium Cholate Surfactant in Aqueous Dispersion

Surfactant-based wet spinning is a promising route toward the eco-friendly production of carbon nanotube fibers (CNTFs). However, currently, the properties of surfactant-based wet-spun CNTFs lag behind those produced by other methods, indicating the need for further understanding and research. Here, we explored the surface characteristics of carbon nanotubes (CNTs) that are advantageous for the properties of CNTFs produced by wet spinning, using sodium cholate as a surfactant. Our finding indicates that appropriate thermal oxidation of CNTs enhances the fiber properties, while excessive oxidation undermines them. This implies that the bonding mechanism between CNTs and sodium cholate involves hydrophobic interaction and π-π interaction. Therefore, it is crucial to preserve a clean surface of CNTs in wet spinning using sodium cholate. We believe our research will contribute to the advancement of surfactant-based wet spinning of CNTFs.

Structurally Aligned Multifunctional Neural Probe (SAMP) Using Forest-Drawn CNT Sheet onto Thermally Drawn Polymer Fiber for Long-Term In Vivo Operation

Neural probe engineering is a dynamic field, driving innovation in neuroscience and addressing scientific and medical demands. Recent advancements involve integrating nanomaterials to improve performance, aiming for sustained in vivo functionality. However, challenges persist due to size, stiffness, complexity, and manufacturing intricacies. To address these issues, a neural interface utilizing freestanding CNT-sheets drawn from CNT-forests integrated onto thermally drawn functional polymer fibers is proposed. This approach yields a device with structural alignment, resulting in exceptional electrical, mechanical, and electrochemical properties while retaining biocompatibility for prolonged periods of implantation. This Structurally Aligned Multifunctional neural Probe (SAMP) employing forest-drawn CNT sheets demonstrates in vivo capabilities in neural recording, neurotransmitter detection, and brain/spinal cord circuit manipulation via optogenetics, maintaining functionality for over a year post-implantation. The straightforward fabrication method's versatility, coupled with the device's functional reliability, underscores the significance of this technique in the next-generation carbon-based implants. Moreover, the device's longevity and multifunctionality position it as a promising platform for long-term neuroscience research.

Knitting Elastic Conductive Fibers of MXene/Natural Rubber for Multifunctional Wearable Sensors

Wearable electronic sensors have recently attracted tremendous attention in applications such as personal health monitoring, human movement detection, and sensory skins as they offer a promising alternative to counterparts made from traditional metallic conductors and bulky metallic conductors. However, the real-world use of most wearable sensors is often hindered by their limited stretchability and sensitivity, and ultimately, their difficulty to integrate into textiles. To overcome these limitations, wearable sensors can incorporate flexible conductive fibers as electrically active components. In this study, we adopt a scalable wet-spinning approach to directly produce flexible and conductive fibers from aqueous mixtures of Ti3C2Tx MXene and natural rubber (NR). The electrical conductivity and stretchability of these fibers were tuned by varying their MXene loading, enabling knittability into textiles for wearable sensors. As individual filaments, these MXene/NR fibers exhibit suitable conductivity dependence on strain variations, making them ideal for motivating sensors. Meanwhile, textiles from knitted MXene/NR fibers demonstrate great stability as capacitive touch sensors. Collectively, we believe that these elastic and conductive MXene/NR-based fibers and textiles are promising candidates for wearable sensors and smart textiles.

From Fluorescence-Transfer-Lightening-Printing-Assisted Conductive Adhesive Nanocomposite Hydrogels toward Wearable Interactive Optical Information-Electronic Strain Sensors

The interactive flexible device, which monitors the human motion in optical and electrical synergistic modes, has attracted growing attention recently. The incorporation of information attribute within the optical signal is deemed advantageous for improving the interactive efficiency. Therefore, the development of wearable optical information-electronic strain sensors holds substantial promise, but integrating and synergizing various functions and realizing strain-mediated information transformation keep challenging. Herein, an amylopectin (AP) modified nanoclay/polyacrylamide-based nanocomposite (NC) hydrogel and an aggregation-induced-emission-active ink are fabricated. Through the fluorescence-transfer printing of the ink onto the hydrogel film in different strains with nested multiple symbolic information, a wearable interactive fluorescent information-electronic strain sensor is developed. In the sensor, the nanoclay plays a synergistic "one-stone-three-birds" role, contributing to "lightening" fluorescence (≈80 times emission intensity enhancement), ionic conductivity, and excellent stretchability (>1000%). The sensor has high biocompatibility, resilience (elastic recovery ratio: 97.8%), and strain sensitivity (gauge factor (GF): 10.9). Additionally, the AP endows the sensor with skin adhesiveness. The sensor can achieve electrical monitoring of human joint movements while displaying interactive fluorescent information transformation. This research poses an efficient strategy to develop multifunctional materials and provides a general platform for achieving next-generation interactive devices with prospective applications in wearable devices, human-machine interfaces, and artificial intelligence.

Fast and Strong Carbon Nanotube Yarn Artificial Muscles by Electro-osmotic Pump

Previous electrochemically powered yarn muscles cannot be usefully operated between extreme negative and extreme positive potentials, since generated stresses during anion injection and cation injection partially cancel because they are in the same direction. We here report an ionomer-infiltrated hybrid carbon nanotube (CNT) yarn muscle that shows unipolar stress behavior in the sense that stress generation between extreme potentials is additive, resulting in an enhanced stress generation. Moreover, the stress generated by this muscle unexpectedly increases with the potential scan rate, which contradicts the fact that scan-rate-induced stress decreases for neat CNT muscles. It is revealed by the electro-osmotic pump effect that the effective ion size injected into the muscle increases with an increase in the scan rate. We demonstrate an electrochemically powered gel-elastomer-yarn muscle adhesive that generates and delivers muscle-contraction-mimicking stimulation to a target tissue.

Soft Fiber/Textile Actuators: From Design Strategies to Diverse Applications

Fiber/textile-based actuators have garnered considerable attention due to their distinctive attributes, encompassing higher degrees of freedom, intriguing deformations, and enhanced adaptability to complex structures. Recent studies highlight the development of advanced fibers and textiles, expanding the application scope of fiber/textile-based actuators across diverse emerging fields. Unlike sheet-like soft actuators, fibers/textiles with intricate structures exhibit versatile movements, such as contraction, coiling, bending, and folding, achieved through adjustable strain and stroke. In this review article, we provide a timely and comprehensive overview of fiber/textile actuators, including structures, fabrication methods, actuation principles, and applications. After discussing the hierarchical structure and deformation of the fiber/textile actuator, we discuss various spinning strategies, detailing the merits and drawbacks of each. Next, we present the actuation principles of fiber/fabric actuators, along with common external stimuli. In addition, we provide a summary of the emerging applications of fiber/textile actuators. Concluding with an assessment of existing challenges and future opportunities, this review aims to provide a valuable perspective on the enticing realm of fiber/textile-based actuators.

Mixed Ionic-Electronic Conducting Hydrogels with Carboxylated Carbon Nanotubes for High Performance Wearable Thermoelectric Harvesters

Mixed ionic-electronic conducting (MIEC) thermoelectric (TE) materials offer higher ionic conductivity and ionic Seebeck coefficient compared to those of purely ionic-conducting TE materials. These characteristics make them suitable for direct use in thermoelectric generators (TEGs) as the charge carriers can be effectively transported from one electrode to the other via the external circuit. In the present study, MIEC hydrogels are fabricated via the chemical cross-linking of polyacrylamide (PAAM) and polydopamine (PDA) to form a double network. In addition, electrically conducting carboxylated carbon nanotubes (CNT-COOH) are dispersed evenly within the hydrogel via sonication and interaction with the PDA. Moreover, the electrical properties of the hydrogel are further improved via the in situ polymerization of polyaniline (PANI). The presence of CNT-COOH facilitates the ionic conductivity and enhances the ionic Seebeck coefficient via ionic-electronic interactions between sodium ions and carboxyl groups on CNT-COOH, which can be observed in X-ray photoelectron spectroscopy results, thereby promoting the charge transport properties. As a result, the optimum device exhibits a remarkable ionic conductivity of 175.3 mS cm-1 and a high ionic Seebeck coefficient of 18.6 mV K-1, giving an ionic power factor (PFi) of 6.06 mW m-1 K-2 with a correspondingly impressive ionic figure of merit (ZTi) of 2.65. These values represent significant achievements within the field of gel-state organic TE materials. Finally, a wearable module is fabricated by embedding the PAAM/PDA/CNT-COOH/PANI hydrogel into a poly(dimethylsiloxane) mold. This configuration yields a high power density of 171.4 mW m-2, thus highlighting the considerable potential for manufacturing TEGs for wearable devices capable of harnessing waste heat.

Porous Polymer Materials in Triboelectric Nanogenerators: A Review

Since the invention of the triboelectric nanogenerator (TENG), porous polymer materials (PPMs), with different geometries and topologies, have been utilized to enhance the output performance and expand the functionality of TENGs. In this review, the basic characteristics and preparation methods of various PPMs are introduced, along with their applications in TENGs on the basis of their roles as electrodes, triboelectric surfaces, and structural materials. According to the pore size and dimensionality, various types of TENGs that are built with hydrogels, aerogels, foams, and fibrous media are classified and their advantages and disadvantages are analyzed. To deepen the understanding of the future development trend, their intelligent and multifunctional applications in human-machine interfaces, smart wearable devices, and self-powering sensors are introduced. Finally, the future directions and challenges of PPMs in TENGs are explored to provide possible guidance on PPMs in various TENG-based intelligent devices and systems.

Cellulose-Based Conductive Materials for Energy and Sensing Applications

Cellulose-based conductive materials (CCMs) have emerged as a promising class of materials with various applications in energy and sensing. This review provides a comprehensive overview of the synthesis methods and properties of CCMs and their applications in batteries, supercapacitors, chemical sensors, biosensors, and mechanical sensors. Derived from renewable resources, cellulose serves as a scaffold for integrating conductive additives such as carbon nanotubes (CNTs), graphene, metal particles, metal-organic frameworks (MOFs), carbides and nitrides of transition metals (MXene), and conductive polymers. This combination results in materials with excellent electrical conductivity while retaining the eco-friendliness and biocompatibility of cellulose. In the field of energy storage, CCMs show great potential for batteries and supercapacitors due to their high surface area, excellent mechanical strength, tunable chemistry, and high porosity. Their flexibility makes them ideal for wearable and flexible electronics, contributing to advances in portable energy storage and electronic integration into various substrates. In addition, CCMs play a key role in sensing applications. Their biocompatibility allows for the development of implantable biosensors and biodegradable environmental sensors to meet the growing demand for health and environmental monitoring. Looking to the future, this review emphasizes the need for scalable synthetic methods, improved mechanical and thermal properties, and exploration of novel cellulose sources and modifications. Continued innovation in CCMs promises to revolutionize sustainable energy storage and sensing technologies, providing environmentally friendly solutions to pressing global challenges.

Rainbow-Colored Carbon Nanotubes via Rational Surface Engineering for Smart Visualized Sensors

Surface engineering is effective for developing materials with novel properties, multifunctionality, and smart features that can enable their use in emerging applications. However, surface engineering of carbon nanotubes (CNTs) to add color properties and functionalities has not been well established. Herein, a new surface engineering strategy is developed to achieve rainbow-colored CNTs with high chroma, high brightness, and strong color travel for visual hydrogen sensing. This approach involved constructing a bilayer structure of W and WO3 on CNTs (CNT/W/WO3 ) and a trilayer structure of W, WO3 , and Pd on CNTs (CNT/W/WO3 /Pd) with tunable thicknesses. The resulting CNT/W/WO3 composite film exhibits a wide range of visible colors, including yellow, orange, magenta, violet, blue, cyan, and green, owing to strong thin-film interference. This coloring method outperforms other structural coloring methods in both brightness and chroma. The smart CNT/W/WO3 /Pd films with porous characteristics quickly and precisely detect the hydrogen leakage site. Furthermore, the smart CNT/W/WO3 /Pd films allow a concentration as low as 0.6% H2 /air to be detected by the naked eye in 58 s, offering a very practical and safe approach for the detection and localization of leaks in onboard hydrogen tanks.

Recent Advances in Carbon Nanotube-Based Energy Harvesting Technologies

There has been enormous interest in technologies that generate electricity from ambient energy such as solar, thermal, and mechanical energy, due to their potential for providing sustainable solutions to the energy crisis. One driving force behind the search for new energy-harvesting technologies is the desire to power sensor networks and portable devices without batteries, such as self-powered wearable electronics, human health monitoring systems, and implantable wireless sensors. Various energy harvesting technologies have been demonstrated in recent years. Among them, electrochemical, hydroelectric, triboelectric, piezoelectric, and thermoelectric nanogenerators have been extensively studied because of their special physical properties, ease of application, and sometimes high obtainable efficiency. Multifunctional carbon nanotubes (CNTs) have attracted much interest in energy harvesting because of their exceptionally high gravimetric power outputs and recently obtained high energy conversion efficiencies. Further development of this field, however, still requires an in-depth understanding of harvesting mechanisms and boosting of the electrical outputs for wider applications. Here, various CNT-based energy harvesting technologies are comprehensively reviewed, focusing on working principles, typical examples, and future improvements. The last section discusses the existing challenges and future directions of CNT-based energy harvesters.

Wet-Driven Bionic Actuators from Wool Artificial Yarn Muscles

Nature-similar muscle is one of the ultimate goals of advanced artificial muscle materials. Currently, a variety of chemical and natural materials have been gradually developed for the preparation of artificial muscles. However, due to the scarcity, biological exclusion, and poor flexibility of the abovementioned materials, it is still a challenging process to maximize the imitation of behaviors shown by real muscles and commercial development. Here, this article presents multidimensional wool yarn artificial muscles, and the wet response behavior of fibers is induced in yarn muscles successfully by virtue of weakening the water-repellent effect of wool scales. Wool artificial muscles are cost-effective and widely available and have good biocompatibility. In addition, wool fiber assemblies are structurally stable, soft, and flexible to be processed into artificial muscles with torsional, contractile, and even multilayered structures, enabling various wet-driven behaviors. On the basis of the theoretical model and numerical simulation, we explained and verified the working mechanism employed in wool artificial yarn muscles. Finally, the yarn muscle was integrated into a wool muscle group through the textile technology, followed by the application to robot bionic arms, displaying the great potential of wool artificial yarn muscles in bionic drivers and the intelligent textile industry.

Fibriform Organic Electrochemical Diodes with Rectifying, Complementary Logic and Transient Voltage Suppression Functions for Wearable E-Textile Embedded Circuits

In this study, a fibriform electrochemical diode capable of performing rectifying, complementary logic and device protection functions for future e-textile circuit systems is fabricated. The diode was fabricated using a simple twisted assembly of metal/polymer semiconductor/ion gel coaxial microfibers and conducting microfiber electrodes. The fibriform diode exhibited a prominent asymmetrical current flow with a rectification ratio of over 10², and its performance was retained after repeated bending deformations and washings. Fundamental studies on the electrochemical interactions of polymer semiconductors with ions reveal that the Faradaic current generated in polymer semiconductors by electrochemical reactions results in an abrupt current increase under a forward bias, in which the threshold voltages of the device are determined by the oxidation or reduction potential of the polymer semiconductor. Textile-embedded full-wave rectifiers and logic gate circuits were implemented by simply integrating the fibriform diodes, exhibiting AC-to-DC signal conversion and logic operation functions, respectively. It was also confirmed that the proposed fibriform diode can suppress transient voltages and thus protect a low-voltage operational wearable e-textile circuit.

Toward a new generation of permeable skin electronics

Skin-mountable electronics are considered to be the future of the next generation of portable electronics, due to their softness and seamless integration with human skin. However, impermeable materials limit device comfort and reliability for long-term, continuous usage. The recent emergence of permeable skin-mountable electronics has attracted tremendous attention in the soft electronics field. Herein, we provide a comprehensive and systematic review of permeable skin-mountable electronics. Typical porous materials and structures are first highlighted, followed by discussion of important device properties. Then, we review the latest representative applications of breathable skin-mountable electronics, such as bioelectrical sensors, temperature sensors, humidity and hydration sensors, strain and pressure sensors, and energy harvesting and storage devices. Finally, a conclusion and future directions for permeable skin electronics are provided.

Versatile Mechanochromic Sensor based on Highly Stretchable Chiral Liquid Crystalline Elastomer

A mechanochromic strain sensor that is capable of distinguishing the orientation, the location, and the degree of deformation based on the highly stretchable membrane of main-chain chiral liquid crystalline elastomer (MCLCE) is proposed. The MCLCE film is designed to exhibit uniform and significant color shift upon the small strain by using step-growth polymerization of liquid crystal (LC) oligomer and its phase-stabilization in solvent mesogen. As conformally placed on the bottom elastomer sheet, the MCLCE film shows multimodal, instantaneous color change for sensing arbitrary in-plane deformation, out-of-plane bending, and nonzero Gaussian deformation. Based on high freedom in the device design, it is also demonstrated that this sensor can display color patterns or encrypted images in response to the localized weight or strain. The simple and straightforward concept proposed here can be applicable in the fields of wearable devices, displays, and soft robotics.

Graphene Interlocking Carbon Nanotubes for High-Strength and High-Conductivity Fibers

Carbon nanotubes (CNTs) are promising building blocks for the fabrication of novel fibers with structural and functional properties. However, the mechanical and electrical performances of carbon nanotube fibers (CNTFs) are far lower than the intrinsic properties of individual CNTs. Exploring methods for the controllable assembly and continuous preparation of high-performance CNTFs is still challenging. Herein, a graphene/chlorosulfonic acid-assisted wet-stretching method is developed to produce highly densified and well-aligned graphene/carbon nanotube fibers (G/CNTFs) with excellent mechanical and electrical performances. Graphene with small size and high quality can bridge the adjacent CNTs to avoid the interfacial slippage under deformation, which facilitates the formation of a robust architecture with abundant conductive pathways. Their ordered structure and enhanced interfacial interactions endow the fibers with both high strength (4.7 GPa) and high electrical conductivity (more than 2 × 10⁶ S/m). G/CNTF-based lightweight wires show good flexibility and knittability, and the high-performance fiber heaters exhibit ultrafast electrothermal response over 1000 °C/s and a low operation voltage of 3 V. This method paves the way for optimizing the microstructures and producing high-strength and high-conductivity CNTFs, which are promising candidates for the high-value fiber-based applications.

Hierarchically Structured Nanoporous Palladium with Ordered/Disordered Channels for Ultrahigh and Fast Strain

Metallic actuators have increasingly shown the potential to replace conventional piezoelectric ceramics and conducting polymers. However, it is still a great challenge to achieve strain amplitudes over 4% while maintaining fast strain responses. Herein, we fabricated bulk nanoporous palladium (NP-Pd) with microsheet-array-like hierarchically nanoporous (MAHNP) structure by dealloying a eutectic Al-Pd precursor. The hierarchical structure consists of array-like microsized channels/sheets and disordered nanosized networks. The locally ordered channels play a critical role in fast mass transport while nanoligaments accumulate a large surface area for hydrogen adsorption/absorption and desorption. Therefore, the MAHNP-Pd not only obtains a fast strain rate with the maximum value close to 1 × 10^-4 s^-1 but also exhibits an ultrahigh strain amplitude of 4.68%, exceeding all reported values for bulk electrochemical metallic actuators to date. Additionally, the superiority of the MAHNP structure is demonstrated in transport kinetics as benchmarked with the scenario of unimodal NP-Pd.

Avant-Garde Polymer and Nano-Graphite-Derived Nanocomposites—Versatility and Implications

Graphite (stacked graphene layers) has been modified in several ways to enhance its potential properties/utilities. One approach is to convert graphite into a unique ‘nano-graphite’ form. Nano-graphite consists of few-layered graphene, multi-layered graphene, graphite nanoplatelets, and other graphene aggregates. Graphite can be converted to nano-graphite using physical and chemical methods. Nano-graphite, similar to graphite, has been reinforced in conducting polymers/thermoplastics/rubbery matrices to develop high-performance nanocomposites. Nano-graphite and polymer/nano-graphite nanomaterials have characteristics that are advantageous over those of pristine graphitic materials. This review basically highlights the essential features, design versatilities, and applications of polymer/nano-graphite nanocomposites in solar cells, electromagnetic shielding, and electronic devices.

Advances in artificial muscles: A brief literature and patent review

Background: Artificial muscles are an active research area now. Methods: A bibliometric analysis was performed to evaluate the development of artificial muscles based on research papers and patents. A detailed overview of artificial muscles' scientific and technological innovation was presented from aspects of productive countries/regions, institutions, journals, researchers, highly cited papers, and emerging topics. Results: 1,743 papers and 1,925 patents were identified after retrieval in Science Citation Index-Expanded (SCI-E) and Derwent Innovations Index (DII). The results show that China, the United States, and Japan are leading in the scientific and technological innovation of artificial muscles. The University of Wollongong has the most publications and Spinks is the most productive author in artificial muscle research. Smart Materials and Structures is the journal most productive in this field. Materials science, mechanical and automation, and robotics are the three fields related to artificial muscles most. Types of artificial muscles like pneumatic artificial muscles (PAMs) and dielectric elastomer actuator (DEA) are maturing. Shape memory alloy (SMA), carbon nanotubes (CNTs), graphene, and other novel materials have shown promising applications in this field. Conclusion: Along with the development of new materials and processes, researchers are paying more attention to the performance improvement and cost reduction of artificial muscles.

A Coiled Carbon Nanotube Yarn-Integrated Surface Electromyography System To Monitor Isotonic and Isometric Movements

A surface electromyogram (sEMG) electrode collects electrical currents generated by neuromuscular activity by a noninvasive technique on the skin. It is particularly attractive for wearable systems for various human activities and health care monitoring. However, it remains challenging to discriminate EMG signals from isotonic (concentric/eccentric) and isometric movements. By applying nanotechnology, we provide a coiled carbon nanotube (CNT) yarn-integrated sEMG device to overcome sEMG-based motion recognition. When the arm was contracted at different angles, the sEMG-derived root mean square amplitude signals were constant regardless of the angle of the moving arm. However, the coiled CNT yarn-derived open circuit voltage (OCV) signals proportionally increased when the arm's angle increased, and presented negative and positive values depending on the moving direction of the arm. Moreover, isometric contraction is characterized by the onset of EMG signals without an OCV signal, and isotonic contraction is determined by both EMG signals and OCV signals. Taken together, the integration of EMG and coiled CNT yarn electrodes provides complementary information, including the strength, direction, and degree of muscle movement. Therefore, we suggest that our system has high potential as a wearable system to monitor human motions in industrial and human system applications.

Controllable Preparation and Strengthening Strategies towards High-Strength Carbon Nanotube Fibers

Carbon nanotubes (CNTs) with superior mechanical properties are expected to play a role in the next generation of critical engineering mechanical materials. Crucial advances have been made in CNTs, as it has been reported that the tensile strength of defect-free CNTs and carbon nanotube bundles can approach the theoretical limit. However, the tensile strength of macro carbon nanotube fibers (CNTFs) is far lower than the theoretical level. Although some reviews have summarized the development of such fiber materials, few of them have focused on the controllable preparation and performance optimization of high-strength CNTFs at different scales. Therefore, in this review, we will analyze the characteristics and latest challenges of multiscale CNTFs in preparation and strength optimization. First, the structure and preparation of CNTs are introduced. Then, the preparation methods and tensile strength characteristics of CNTFs at different scales are discussed. Based on the analysis of tensile fracture, we summarize some typical strategies for optimizing tensile performance around defect and tube-tube interaction control. Finally, we introduce some emerging applications for CNTFs in mechanics. This review aims to provide insights and prospects for the controllable preparation of CNTFs with ultra-high tensile strength for emerging cutting-edge applications.

A 'Moore's law' for fibers enables intelligent fabrics

Fabrics are an indispensable part of our everyday life. They provide us with protection, offer privacy and form an intimate expression of ourselves through their esthetics. Imparting functionality at the fiber level represents an intriguing path toward innovative fabrics with a hitherto unparalleled functionality and value. The fiber technology based on thermal drawing of a preform, which is identical in its materials and geometry to the final fiber, has emerged as a powerful platform for the production of exquisite fibers with prerequisite composition, geometric complexity and control over feature size. A 'Moore's law' for fibers is emerging, delivering higher forms of function that are important for a broad spectrum of practical applications in healthcare, sports, robotics, space exploration, etc. In this review, we survey progress in thermally drawn fibers and devices, and discuss their relevance to 'smart' fabrics. A new generation of fabrics that can see, hear and speak, sense, communicate, harvest and store energy, as well as store and process data is anticipated. We conclude with a critical analysis of existing challenges and opportunities currently faced by thermally drawn fibers and fabrics that are expected to become sophisticated platforms delivering value-added services for our society.

Elastic Kernmantle E-Braids for High-Impact Sports Monitoring

The kernmantle construction, a kind of braiding structure that is characterized by the kern absorbing most of the stress and the mantle protecting the kern, is widely employed in the field of loading and rescue services, but rarely in flexible electronics. Here, a novel kernmantle electronic braid (E-braid) for high-impact sports monitoring, is proposed. The as-fabricated E-braids not only demonstrate high strength (31 Mpa), customized elasticity, and nice machine washability (>500 washes) but also exhibit excellent electrical stability (>200 000 cycles) during stretching. For demonstration, the E-braids are mounted to different parts of the trampoline for athletes' locomotor behavior monitoring. Furthermore, the E-braids are proved to act as multifarious intelligent sports gear or wearable equipment such as electronic jump rope and respiration monitoring belt. This study expands the kernmantle structure to soft flexible electronics and then accelerates the development of quantitative analysis in modern sports industry and athletes' healthcare.

Femtosecond Laser Bessel Beam Fabrication of a Supercapacitor with a Nanoscale Electrode Gap for High Specific Volumetric Capacitance

Supercapacitors are widely used in electronic systems as energy storage devices. The fabrication of a miniaturized supercapacitor with high specific capacitance has attracted much attention in recent years. Here, we propose a new method to fabricate supercapacitors with a nanoscale electrode gap by using a femtosecond laser. The original femtosecond laser was converted to a nondiffraction Bessel light field with nanoscale beam width and microscale focal depth. Nanoscale processing precision was achieved by regulating the Bessel beam. We fabricated graphene supercapacitors with different electrode gap widths (varying from the microscale to the nanoscale) using this method. Supercapacitors fabricated by this method have advantages in both size miniaturization (electrode gap width down to ∼500 nm) and electrochemical performance improvement (a specific volumetric capacitance of 195 F/cm³). This work demonstrates that the femtosecond laser Bessel beam processing method provides a reliable pathway to fabricate miniaturized supercapacitors with high specific capacitance and other nanoscale electronic devices.

Excellent Photonic and Mechanical Properties of Macromorphic Fibers Formed by Eu3+-Complex-Anchored, Unzipped, Multiwalled Carbon Nanotubes

The macromorphic properties of carbon nanotubes perform poorly because of their size limitations: nanosize in diameters and microsize in length. In this work, to realize these dual purposes, we first used an electrochemical method to tear the surface of multiwalled carbon nanotubes (MWCNTs) to anchor photonic Eu3+-complexes there. Through the polar reactive groups endowed by the tearing, the Eu3+-complexes coordinate at the defected structures, obtaining the Eu3+-complex-anchored, unzipped, multiwalled carbon nanotubes (E-uMWCNTs). The controllable surface-breaking retains the MWCNTs' original, excellent mechanical properties. Then, to obtain the macromorphic structure with infinitely long fibers, a wet-spinning process was applied via the binding of a small quantity of polyvinyl alcohol (PVA). Thus, the wet-spun fibers with high contents of E-uMWCNTs (E-uMWCNT-Fs) were produced, in which the E-uMWCNTs took 33.3 wt%, a high ratio in E-uMWCNT-Fs. On the other hand, due to the reinforcing effect of E-uMWCNTs, the highest tensile strength can reach 228.2 MPa for E-uMWCNT-Fs. Meanwhile, the E-uMWCNT-Fs show high-efficiency photoluminescence and excellent media resistance performance due to the embedding effect of PVA on the E-uMWCNTs. Therefore, E-uMWCNT-Fs can exhibit excellent luminescence properties in aqueous solutions at pH 4~12 and in some high-concentration metal-ion solutions. Those distinguished performances promise outstanding innovations of this work.

Silk Fiber Multiwalled Carbon Nanotube-Based Micro-/Nanofiber Composite as a Conductive Fiber and a Force Sensor

Silk cocoon fibers (SFs) are natural polymers that are made up of fibroin protein. These natural fibers have higher mechanical stability and good elasticity properties. In this work, we coated multiwalled carbon nanotubes (MWCNTs) on the surface of SFs using a simple stirring technique with vinegar as the medium. This SF-MWCNT micro-/nanofiber composite was prepared without any adhesives. The characterization results revealed that the SF-MWCNT micro-/nanofiber composite exhibited excellent electrical conductivity (995 Ω cm^-1), tensile strength (up to 200% greater elongation), and durability characteristics. In addition, this micro-/nanofiber composite shows a change in resistance from 1450 to 960 Ω cm^-1 for an applied mechanical force of 0.3-1 N kg^-1. Based on our findings, SF-MWCNT micro-/nanofiber composite-based conductive fibers (CFs) and force sensors (FSs) were developed.

Toward a Multifunctional Light-Driven Biomimetic Mudskipper-Like Robot for Various Application Scenarios

The systematicness, flexibility, and complexity of natural biological organisms are a constant stream of inspiration for researchers. Therefore, mimicking the natural intelligence system to develop microrobotics has attracted broad interests. However, developing a multifunctional device for various application scenarios has great challenges. Herein, we present a bionic multifunctional actuation device─a light-driven mudskipper-like actuator that is composed of a porous silicone elastomer and graphene oxide. The actuator exhibits a reversible and well-integrated response to near-infrared (NIR) light due to the photothermal-induced contractile stress in the actuation film, which promotes generation of cyclical and rapid locomotion upon NIR light being switched on and off, such as bending in air and crawling in liquid. Furthermore, through rational device design and modulation of light, the mechanically versatile device can float and swim controllably following a predesigned route at the liquid/air interface. More interestingly, the actuator can jump from liquid medium to air with an extremely short response time (400 ms), a maximum speed of 2 m s^-1, and a height of 14.3 cm under the stimulation of near-infrared light. The present work possesses great potential in the applications of bioinspired actuators in various fields, such as microrobots, sensors, and locomotion.

An Overview of Hierarchical Design of Textile-Based Sensor in Wearable Electronics

Smart textiles have recently aroused tremendous interests over the world because of their broad applications in wearable electronics, such as human healthcare, human motion detection, and intelligent robotics. Sensors are the primary components of wearable and flexible electronics, which convert various signals and external stimuli into electrical signals. While traditional electronic sensors based on rigid silicon wafers can hardly conformably attach on the human body, textile materials including fabrics, yarns, and fibers afford promising alternatives due to their characteristics including light weight, flexibility, and breathability. Of fundamental importance are the needs for fabrics simultaneously having high electrical and mechanical performance. This article focused on the hierarchical design of the textile-based flexible sensor from a structure point of view. We first reviewed the selection of newly developed functional materials for textile-based sensors, including metals, conductive polymers, carbon nanomaterials, and other two-dimensional (2D) materials. Then, the hierarchical structure design principles on different levels from microscale to macroscale were discussed in detail. Special emphasis was placed on the microstructure control of fibers, configurational engineering of yarn, and pattern design of fabrics. Finally, the remaining challenges toward industrialization and commercialization that exist to date were presented.

High-Performance and Reliable White Organic Light-Emitting Fibers for Truly Wearable Textile Displays

Light-emitting fibers have been intensively developed for the realization of textile displays and various lighting applications, as promising free-form electronics with outstanding interconnectivity. These advances in the fiber displays have been made possible by the successful implementation of the core technologies of conventional displays, including high optoelectronic performance and essential elements, in the fiber form-factor. However, although white organic light-emitting diodes (WOLEDs), as a fundamental core technology of displays, are essential for realizing full-color displays and solid-state lighting, fiber-based WOLEDs are still challenging due to structural issues and the lack of approaches to implementing WOLEDs on fiber. Herein, the first fiber WOLED is reported, exhibiting high optoelectronic performance and a reliable color index, comparable to those of conventional planar WOLEDs. As key features, it is found that WOLEDs can be successfully introduced on a cylindrical fiber using a dip-coatable single white-emission layer based on simulation and optimization of the white spectra. Furthermore, to ensure durability from usage, the fiber WOLED is encapsulated by an Al2 O3 /elastomer bilayer, showing stable operation under repetitive bending and pressure, and in water. This pioneering work is believed to provide building blocks for realizing complete textile display technologies by complementing the lack of the core technology.

Photosensitive-Stamp-Inspired Scalable Fabrication Strategy of Wearable Sensing Arrays for Noninvasive Real-Time Sweat Analysis

Wearable sweat sensing is essential to the development of personalized health monitoring in a noninvasive manner with molecular-level insight. Hence, there is an increasing demand for convenient, facile, and efficient fabrication of wearable sensing arrays. Inspired by a photosensitive stamp (PS), we present herein a simple, low-cost, and eco-friendly vacuum filtration-transfer printing method (termed PS-VFTP) for the scalable preparation of single-walled carbon nanotube (SWCNT) based flexible electrode arrays. This method can economically yield customized flexible SWCNT arrays with praiseworthy performance, such as high reproducibility, precision, uniformity, conductivity, and mechanical stability. In addition, the flexible SWCNT arrays can be easily functionalized into high-performance electrochemical sensors for the simultaneous monitoring of sweat metabolites (glucose, lactate) and electrolytes (Na⁺, K⁺). The integration of wearable sensing arrays with a signal acquisition and processing circuit system in the intelligent wearable sensors empowers them to realize noninvasive, real-time, and in situ sweat analysis during exercise. More meaningfully, such a PS-VFTP strategy can be easily expanded to the economical manufacturing of other flexible electronic devices.