Stretchable Conductive Fibers Research Articles

Silver nanoparticles bridging liquid metal for wearable electromagnetic interference fabric

Stretchable conductive fibers are essential for the advancement of wearable electronic textiles. However, a significant challenge arises as their conductivity sharply decreases when stretched due to disruptions in electronic transport. Coating fibers with soft liquid metal (LM) has emerged as a promising solution. Despite this, there remains an urgent need to develop methods that enhance LM adhesion to substrates while facilitating efficient electron transport pathways. This study demonstrates a novel Ag-LM conductive network strategy for fabricating a thermoplastic polyurethane/polydopamine/silver-LM (TPU/PDA/Ag-LM) fiber membrane. This membrane exhibits outstanding stretchable electromagnetic interference (EMI) shielding performance and is produced through straightforward electrospinning, electroless depositing, and LM coating and activation. The TPU/PDA/Ag fiber membrane is initially prepared via polydopamine-assisted deposition of silver nanoparticles (AgNPs) on electrospun TPU fibers. The presence of AgNPs on the surface of TPU/PDA fibers enhances LM adhesion to the substrate and bridges adjacent LM to establish efficient conductive paths. This interaction benefits from the reactive alloying between AgNPs and LM, where the LM infiltrates the gaps among AgNPs, forming a distinctive LM-Ag alloy layer that uniformly coats the surface of TPU fibers. As anticipated, the unique three-dimensional (3D) interconnected LM-Ag conductive network remains intact during stretching, ensuring strain-invariant conductivity. The fabricated TPU/PDA/Ag-LM fiber membrane demonstrates exceptional EMI shielding effectiveness (SE) of 77.4 dB within the frequency range of 8.2–12.8 GHz and maintains an excellent EMI SE of 37.2 dB under extensive tensile deformation of 300%. Furthermore, the TPU/PDA/Ag-LM fiber membrane shows remarkable mechanical properties and stable Joule heating performance even under significant stretching.

Highly Stretchable Composite Conductive Fibers (SCCFs) and Their Applications.

Stretchable composite conductive fibers (SCCFs) exhibit remarkable conductivity, stretchability, breathability, and biocompatibility, making them ideal candidates for wearable electronics and bioelectronics. The exploitation of SCCFs in electronic devices requires a careful balance of many aspects, including material selection and process methodologies, to address the complex challenges associated with their electrical and mechanical properties. In this review, we elucidate the conductive mechanism of SCCFs and summarize strategies for integrating various conductors with stretchable fibers, emphasizing the primary challenges in fabricating highly conductive fibers. Furthermore, we explore the multifaceted applications of SCCFs-based frameworks in wearable electronic devices. This review aims to emphasize the significance of SCCFs and offers insights into their conductive mechanisms, material selection, manufacturing technologies, and performance improvement. Hopefully, it can guide the innovative development of SCCFs and broaden their application potential.

Advancing infrared display technology with carbon nanotube-embedded spandex fibers

We report on developing a wearable infrared (IR) display based on stretchable conductive fibers fabricated through an expansion–contraction process. The expansion process creates a gap between the strands of spandex fibers. This is achieved by immersing the fibers in a solvent where carbon nanotubes (CNTs) are dispersed, thereby embedding the CNTs. Contraction is achieved through a drying process, which removes the gap between the strands of the spandex fibers. This ensures that the CNTs remain embedded, even after repeated stretching. The CNT-embedded spandex fibers are arranged into a 5 × 7 pixel array. The intensity of the IR rays emitted from the fibers can be controlled by adjusting their temperature, which is achieved by varying the driving voltage. Full-color IR images and displays of letters and numbers are realized through precise control of the IR light intensity. The wearable IR display developed in this study opens up exciting possibilities for integration into advanced systems such as military identification, artificial intelligence robots, autonomous driving, and aerospace industry applications.

All-Polymeric stretchable conductive fiber with versatile intelligent wearable applications via microfluidic spinning technology

It remains a great challenge to fabricate all-polymer stretchable conductive fibers simultaneously presenting high mechanical robustness, high stretchability, and high conductivity through convenient and fast process, even though they exhibit great application potential in the intelligent wearable fields in replacement of the traditional metal wires or the liquid metal-based conductive fibers. In this paper, an all-polymeric fiber with core–shell structure is continuously produced through co-axial microfluidic spinning strategy. The composition of the fluids and the processing parameters of MST are regulated to adjust the size of the obtained PU@PEDOT:PSS fiber, and then optimizing its electric properties and the mechanical performances. The polyurethane (PU) elastic shell layer and the H2SO4-doped PEDOT:PSS conductive core provide the obtained composite fiber with a high conductivity exceeding 220 S m−1, as well as an impressive stretchability up to above 400 % strain, thus endowing it with versatile intelligent wearable applications, including the super-sensitive strain sensor for human motions monitoring, textile-based triboelectric nanogenerator for self-powered impact sensing, and the electro-thermal conversion fabric for keep warming.

Dopamine-induced high fiber wetness for improved conductive fiber bundles with striated polypyrrole coating toward wearable healthcare electronics

Stretchable conductive fibers have shown considerable promise in the field of wearable healthcare electronics, but their widespread application has been impeded by the complexity of their manufacturing processes and their susceptibility to electrical failure under significant deformations. In response to this challenge, this study proposes an approach that harnesses dopamine to enhance the wettability of commercial polyurethane (PU) multifilaments. This enhancement facilitates the penetration of aqueous solutions into the core layer of the multifilaments, thereby enabling the polymerization of a striated polypyrrole (PPy) coating on the monofilament surface of the multifilament core layer. The resulting dopamine-induced composite fiber bundles (DCFBs), drawing inspiration from the structure of striated muscle fiber bundles, demonstrates insensitive conductivity at a high tensile strain of 600% and exceptional durability exceeding 40,000 cycles, as the bionic structure mitigates the effect of PPy coating cracks on overall conductivity. The bionic DCFBs holds potential for applications in stretchable electrical circuits, all-weather wearable thermal therapy devices, and pressure sensors for Moss Code communication and human state detection. This work presents a straightforward and versatile technique for producing highly stretchable fibers with multilayer conductive coatings featuring microstructures in the context of wearable healthcare electronics, utilizing commercial fibers as the primary material source.

Stretchable Fibers with Highly Conductive Surfaces and Robust Electromechanical Performances for Electronic Textiles.

One-dimensional conductive fibers that can simultaneously accommodate multiple deformations are crucial materials to enable next-generation electronic textile technologies for applications in the fields of healthcare, energy harvesting, human-machine interactions, etc. Stretchable conductive fibers (SCFs) with high conductivity on their external structure are important for their direct integration with other electronic components. However, the dilemma to achieve high conductivity and concurrently large stretchability is still quite challenging to resolve among conductive fibers with a conductive surface. Here, a three-layer coaxial conductive fiber, which can provide robust electrical performance under various deformations, is reported. A dual conducting structure with a semisolid metallic layer and a stretchable composite layer was designed in the fibers, providing exceptional conductivity and mechanical stability under mechanical strains. The conductive fiber achieved an initial conductivity of 2291.83 S cm-1 on the entire fiber and could be stretched up to 600% strains. With the excellent electromechanical properties of the SCF, we were able to demonstrate different electronic textile applications including physiological monitoring, neuromuscular electrical stimulation, and energy harvesting.

Continuous Melt Spinning of Adaptable Covalently Cross-Linked Self-Healing Ionogel Fibers for Multi-Functional Ionotronics.

Stretchable conductive fibers play key roles in electronic textiles, which have substantial improvements in terms of flexibility, breathability, and comfort. Compared to most existing electron-conductive fibers, ion-conductive fibers are usually soft, stretchable, and transparent, leading to increasing attention. However, the integration of desirable functions including high transparency, stretchability, conductivity, solvent resistance, self-healing ability, processability, and recyclability remains a challenge to be addressed. Herein, a new molecular strategy based on dynamic covalent cross-linking networks is developed to enable continuous melt spinning of the ionogel fiber with the aforementioned properties. As a proof of concept, adaptable covalently cross-linked ionogel fibers based on dimethylglyoximeurethane (DOU) groups (DOU-IG fiber) are prepared. The resultant DOU-IG fiber exhibited high transparency (>93%), tensile strength (0.76MPa), stretchability (784%), and solvent resistance. Owing to the dynamic of DOU groups, the DOU-IG fiber shows high healing performance using near-infrared light. Taking advantage of DOU-IG fibers, multifunctional ionotronics with the integration of several desirable functionalities including sensor, triboelectric nanogenerator, and electroluminescent display are fabricated and used for motion monitoring, energy harvesting, and human-machine interaction. It is believed that these DOU-IG fibers are promising for fabricating the next generation of electronic textiles and other wearable electronics.

A reduction-driven directed aggregation strategy for fabricating stretchable conductive core-sheath fibers in wearable electronics

Rapid advancement of wearable electronics is profoundly reshaping our daily lives. At the heart of these innovations, stretchable conductive fibers (SCFs) assume pivotal roles in the high-sensitivity strain sensing and the high-conductivity flexible electrical conduction. Here, the stretchable conductive core-sheath fibers (SCCFs) are developed by a reduction-driven directed aggregation strategy. A conductive sheath layer of the silver nanoparticles aggregation and an elastic core layer of polymer matrix constitute an SCCF with the effective interface bonding. An SCCF with the high initial conductivity of over 1.77 × 105 S m−1 is fabricated with the features of reliability and good washability through the systematic optimization. On one hand, leveraging the microcrack effect, the strain sensing with the high resistance sensitivity under subtle strain is achieved by using a straight SCCF. On the other hand, the SCCF with a three-dimensional helical structure is designed to act as the flexible electrical conduction with the low resistance sensitivity under great strain. Notably, these SCCFs not only exhibit exceptional sensitivity for monitoring human movements, but also demonstrate efficient electrical energy conduction capabilities. This work proposes a prospective strategy to fabricate the versatile SCFs with great reliability, stability, and durability for wearable electronics.

Thread-analogous elastic fibers with liquid metal core by drawing at room temperature for multifunctional smart textiles

Stretchable and elastic conductive fibers with liquid metal core are appealing for integration into electronic fabrics and clothing, owing to their inherent electrical conductivity even under strain. Previously, injecting liquid metal into core of hollow elastic fiber has been utilized to fabricate conductive fibers, however, hydrodynamics limits the extent to which metals can be injected, thus limiting length and cross-sectional area. Although direct printing and spinning methods using coaxial needles have been utilized to fabricate long and thin polymer-encased liquid metal fibers via single step, various parameters including extrusion rate along with viscosity and surface tension of liquid metal and polymeric shell, needs to be considered. Herein, we introduce a simple and facile method for fabricating thread analogous conductive fibers by plastically deforming liquid metal injected polymeric shell via drawing at room temperature. This simple yet effective process generates long conductive fibers with narrow cross-sectional area of the liquid metal wire continuously formed along its length. The obtained fiber can withstand deformation arising from daily activities while maintaining excellent electrical performance, thus can be used for fabricating smart textiles serving multitude of purposes.

Template-Free and Stretchable Conductive Fiber with a Built-In Helical Structure for Strain-Insensitive Signal Transmission.

With the rapid development of intelligent electronic devices, conductive fibers have become very critical to signal transmission devices. However, metal-based rigid conductive wires, such as high-modulus copper and silver wires, are prone to signal failure owing to tensile breakage under large strain conditions. Therefore, strain-insensitive stretchable conductive fibers for signal transmission are critical for next-generation wearable devices. Herein, a stretchable conductive fiber with a built-in helical structure is constructed by a "speed discrepancy" fiber-coating strategy with mass scalable production (60 cm/min). Such a "speed discrepancy" strategy is the key mechanism to template-free fabricate a built-in helical structure of the stretchable conductive fiber. The resultant fiber exhibits high conductivity (873 S/cm), stable insensitive signal transmission with a high quality factor (47.4), and a low relative resistance change (∼6%) under large strain. The built-in helical structure inspired by loofah whiskers endows the fiber with excellent strain insensitivity, and it can withstand large strains. On the proof of concept, our fiber can be seamlessly knitted, woven, and braided into smart textiles as an ideal signal transmission device under large strains, which will undoubtedly promote the development of intelligent electronic textiles and next-generation wearable devices.

Scalable production of stretchable conductive fibers for textile electronics

Stretchable conductive fibers are key building blocks for constructing textile electronics. In this Preview, we highlight the scalable production of stretchable conductive fibers based on multimaterial thermal drawing and chemical deposition. The resulting fibers exhibit initial electrical conductivities up to 4,415 S/cm while retaining more than 500% stretchability. They can be further made into multifilaments, driving the development of textile electronics toward real-world applications. Stretchable conductive fibers are key building blocks for constructing textile electronics. In this Preview, we highlight the scalable production of stretchable conductive fibers based on multimaterial thermal drawing and chemical deposition. The resulting fibers exhibit initial electrical conductivities up to 4,415 S/cm while retaining more than 500% stretchability. They can be further made into multifilaments, driving the development of textile electronics toward real-world applications. Stretchable and conductive fibers fabricated by a continuous method for wearable devicesMa et al.Cell Reports Physical ScienceFebruary 21, 2023In BriefMa et al. develop a continuous approach for fabricating stretchable and conductive fibers, which are suitable for being twisted into textile yarns, woven and knitted into textile fabrics, or braided and stitched onto textile structures. These textiles can be assembled into breathable and washable devices for wearable electronic applications. Full-Text PDF Open Access

Stretchable and self-healing conductive fibers from hierarchical silver nanowires-assembled network

Stretchable and self-healing conductive fibers from hierarchical silver nanowires-assembled network

Multifunctional Electronic Textiles by Direct 3D Printing of Stretchable Conductive Fibers

AbstractThe integration of functional fibers into wearable devices by traditional methods is commonly completed in weaving. A new post‐weaving method of integrating fiber devices into textiles is needed to address the challenge of incorporating functional fiber into ready‐made garments without tearing down the clothing and re‐weaving. A 3D printing method to simultaneously fabricate and integrate highly stretchable conductive fiber into ready‐made garments with designed patterns is presented. The fabricated sheath–core fiber consists of a styrene–ethylene–butylene–styrene (SEBS) shell and a Ga–In–Sn alloy liquid metal core. The SEBS shell guarantees the high stretchability (up to 600%) and flexibility, while the liquid metal core offers a high conductivity maintained at large deformation. It is shown that sophisticated patterns, which have millimeter‐level‐resolution that are difficult to be integrated into textiles by weaving, and even more laborious to be incorporated into ready‐made garments, can now be easily modified and implemented into both textiles and ready‐made garments by a time‐saving and low‐cost 3D printing method. Utilizing the electrical characteristics of the fiber in pre‐designed patterns, on‐clothing soft electronics can be printed directly. A printed on‐clothing strain sensor, bending sensor, wireless charging coil, and a touch‐sensing network are demonstrated to show the potential applications in wearable electronics.

Liquid Metal Enabled Elastic Conductive Fibers for Self‐Powered Wearable Sensors

AbstractRealizing stretchable conductive fibers with a trade‐off between stretchability and conductivity is important for wearables. Fibrous triboelectric nanogenerators (FTENGs) represent a promising device for wearable power sources and self‐powered sensors. However, the relationship between conductivity and triboelectric outputs of FTENG remains unfathomed. Herein, a simple strategy for fabricating stretchable conductive fibers with binary rigid‐soft conductive components and dynamic compensation conductive capability is reported. Wet‐spun thermoplastic polyurethane (TPU)/silver flakes (AgFKs) (TA) composite fiber is fabricated and coated by a water‐borne polyurethane (WPU) thin layer, bridging the subsequent liquid metal (LM) coating to obtain TPU/AgFKs/WPU/LM (TAWL) fibers. The TAWL fiber shows outstanding elongation (~600% strain), electrical conductivity of ~2 Ω cm−1 (~3125 S cm−1), and reversible resistance response within 70% tensile strain. Encapsulated by polydimethylsiloxane (PDMS), the TAWL fiber is demonstrated as single electrode FTENG with the maximum output voltage, current, and transferred charge of 7.5 V, 167 nA, and 3.2 nC, respectively. The FTENG shows 150% stretchability without output dropping, demonstrating the superiority of TAWL fibers to sustain large deformation and conductivity degradation but maintain stable triboelectric outputs. As self‐powered sensors, the FTENG can detect joint bending such as for fingers, elbows, and knees, as well as for pressure and location identification.

One-step coaxial spinning of core-sheath hydrogel fibers for stretchable ionic strain sensors

High-strength, highly conductive, and stretchable conductive fibers are essential for the development of flexible electronic devices. Here, we develop a continuous coaxial wet-spinning method to fabricate stretchable, conductive, and freeze-resistant hydrogel fibers with a core-sheath structure. The core is a supramolecular hydrogel, poly (APhe-co-AAm) (PAPAM), obtained by radical polymerization of acrylamide (AAm) and acryloyl-l-phenylalanine (APhe), and the sheath consists of PVDF-HFP and PU with hydrochloric acid as the coagulation bath. The hydrogel fibers exhibit excellent mechanical properties with a tensile strength of 3.1 MPa and elongation at a break of 750 %. Hydrochloric acid plays two roles in this system: one is to promote hydrophobic association and hydrogen bond formation and improves mechanical properties, and the other is to provide plentiful ions to confer excellent electrical conductivity (10.59 S m−1) and freezing resistance (-20 °C). The application of fiber strain sensors for detecting human motion and pressure sensing demonstrates great potential as wearable electronic devices.

Stretchable Composite Conductive Fibers for Wearables

AbstractFibers and textiles are attractive substrates for constructing wearables, the devices rely on conductive fibers with good stretchability to realize electrical conductivity and mechanical adaptivity. The exploitation of stretchable composite conductive fibers (SCCFs) requires diverse strategies in material options and process methods, tackling the challenge in balancing electrical and mechanical properties for ultrafine fiber, which highly determine the properties and applications. In this article, first the working mechanism and advantages of the SCCFs in wearables is introduced. Second, different conductive fillers as well as their respective incorporation strategies and performance superiorities in fabricating SCCFs are systematically summarized. Third, the integration routes of the conductive fillers in SCCFs are indicated and compared, presenting different fabrication strategies and mechanisms for improving the performance of SCCFs. Thereafter, the typical applications of SCCFs in energy management, sensing, actuators, heaters, and displays are highlighted. Accordingly, the main challenges of SCCFs for wearable applications are indicated, and the possible solutions for challenges tackling are proposed. This review prepared aims to highlight the importance of SCCFs in wearables, and provides insights in terms of mechanism, materials, fabrication, and performance improvement, paving a referable way to promote the innovative exploitation and development of SCCFs, extending the application scenarios.

MXene-Reinforced Liquid Metal/Polymer Fibers via Interface Engineering for Wearable Multifunctional Textiles.

Stretchable conductive fibers are an important component of wearable electronic textiles, but often suffer from a decrease in conductivity upon stretching. The use of liquid metal (LM) droplets as conductive fillers in elastic fibers is a promising solution. However, there is an urgent need to develop effective strategies to achieve high adhesion of LM droplets to substrates and establish efficient electron transport paths between droplets. Here, we use large-sized MXene two-dimensional conductive materials to modify magnetic LM droplets and prepare MXene/magnetic LM/poly(styrene-butadiene-styrene) composite fibers (MLMS fibers). The MXene sheets decorated on the surface of magnetic LM droplets not only enhance the droplet adhesion to substrate but also bridge adjacent droplets to establish efficient conductive paths. MLMS fibers show several-fold improvements in tensile strength and elongation and a 30-fold increase in conductivity compared with pure LM-filled fibers. These conductive fibers can be easily woven into multifunctional textiles, which exhibit strong electromagnetic interference shielding and stable Joule heating performances even under large tensile deformation. In addition, other advantages of MLMS textiles, such as high gas/liquid permeability, strong chemical resistance (acid and alkaline conditions), high/low-temperature tolerance (-40-150 °C) and water washability, make them particularly suitable for wearable applications.

Polydimethylsiloxane-based stretchable conductive elastomer fiber by using oil bath-spinning for wearable devices

Flexible stretchable conductors are widely used in various wearable devices and flexible electronic components due to their unique engineering structure adaptability. Fiber has anisotropic stretchability due to its linear structure and it is used in the study of stretchable conductors. However, traditional fibers have low axial stretchability and poor adhesion to conductive particles, so they are not suitable for high-strain engineering structures. Here, a simple and fast preparation method with oil bath thermal curing and a blade coating method is proposed to obtain polydimethylsiloxane-based stretchable elastomer fibers. The fibers have excellent flexibility, stretchability (greater than 100%), elasticity (recovery rate greater than 96%), conductivity (176.5 S/m), and rapid electromechanical response. In particular, the fibers have good weaving ability for their stable performance under bending and twisting load, which is important to weave flexible high conductivity fabric. The effect of conductive particle types (carbon black, carboxylated multi-arm carbon nanotubes) on the fiber properties is also studied. The results show that the carbon nanotube/polydimethylsiloxane fiber has better stable performance under bending and twisting load due to a uniform and dense conductive layer formed. This work provides a research basis for the preparation of silicone rubber-like fibrous composite materials, and the prepared polydimethylsiloxane-based stretchable conductive elastomer fibers have broad application prospects in flexible wearable electronic devices.

Stretchable, Environment-Stable, and Knittable Ionic Conducting Fibers Based on Metallogels for Wearable Wide-Range and Durable Strain Sensors.

The construction of fibrous ionic conductors and sensors with large stretchability, low-temperature tolerance, and environmental stability is highly desired for practical wearable devices yet is challenging. Herein, metallogels (MOGs) with a rapidly reversible force-stimulated sol-gel transition were employed and encapsulated into a hollow thermoplastic elastomer (TPE) microfiber through a simple coaxial spinning. The resultant MOG@TPE coaxial fiber exhibited a high stretchability (>100%) in a broad temperature range (-50 to 50 °C). The MOG@TPE fibrous strain sensor demonstrated a high-yet-linear working curve, fast response time (<100 ms), highly stable conductivity under large deformation, and excellent cycling stability (>3000 cycles). The MOG@TPE fibrous sensors were demonstrated to be directly attached to the human skin to monitor the real-time movements of large/facet joints of the elbow, wrist, finger, and knee. It is believed that the present work for preparing the stretchable ionic conductive fibers holds great promise for applications in fibrous wearable sensors with broad temperature range, large stretchability, stable conductivity, and high wearing comfort.

Screen-printed conductive pattern on spandex for stretchable electronic textiles

Current stretchable conductive fibers used for electronic textiles have received significant attention, but the fiber-based electronic textiles restrict the elaborate patterning due to the limited weaving process. To fabricate electrical circuits on textiles directly to ultimately combine various electronic devices, different approaches would be required to allow the pattern printing onto the stretchable fabric. Here, screen-printing was taken to prepare a highly durable, stretchable conductive pattern on spandex with elastic recovery and high washing durability. A zigzag pattern with the right angle was selected as an optimal shape to prevent the failure of conductive paste from the spandex after stretching cycles. The pattern can successfully diverge the stress by stretching to the of applied one, which enables the conductive characteristic to maintain from the stress under the range of elastic recovery. Another key issue of wearable electronic textiles is the ability to operate under mechanical stress. Encapsulation is an easy modification method to allow the electrical characteristic of the conductive pattern on the spandex when stretched. We confirmed the pattern after encapsulation could act as conductive wires under the stretching deformation of 18% that was much higher than that of the pattern without encapsulation (7%). Consequently, the results suggest potential and further modification methods to fabricate high durable, stretchable electronic textiles.