Stretchable Fibers Research Articles

Competitive proton-trapping strategy enhanced anti-freezing organohydrogel fibers for high-strain-sensitivity wearable sensors.

Stretchable organohydrogel fibers are attracting considerable interest for next-generation flexible and wearable soft strain sensors due to their excellent stability in harsh environments. However, due to the uniformly distributed ions and reduced number of carriers in the whole material, the sensitivity of organohydrogel fibers under subzero temperature is not desirable, which significantly hinders their practical application. Herein, a newly competitive proton-trapping strategy was designed to obtain anti-freezing organohydrogel fibers for high-performance wearable strain sensors via a simple freezing-thawing process, in which tetraaniline (TANI), serving as the proton trapper, and representing the shortest repeated structural unit of polyaniline (PANI), was physically crosslinked with polyvinyl alcohol (PVA) (PTOH). The as-prepared PTOH fiber exhibited an outstanding sensing performance at -40 °C due to the unevenly distributed ion carriers and the highly breakable proton-migration pathways, with a high gauge factor of 24.6 at a strain of 200-300%. Moreover, the existence of hydrogen bonds between the TANI and PVA chains endowed PTOH with a high tensile strength (1.96 MPa) and toughness (8.0 MJ m-3). Accordingly, strain sensors made from PTOH fibers and knitted textiles could monitor human motions rapidly and sensitively, demonstrating their potential as wearable anti-freezing anisotropic strain sensors.

An electrically stable and mechanically robust stretchable fiber conductor prepared by dip-coating silver nanowires on porous elastomer yarn

Super-stretchable fiber conductor with high conductivity and robust mechanical endurance is fabricated by simply dip-coating silver nanowires on electrospun elastomer yarn.

Shape-Programmable Liquid Metal Fibers

Conductive and stretchable fibers are the cornerstone of intelligent textiles and imperceptible electronics. Among existing fiber conductors, gallium-based liquid metals (LMs) featuring high conductivity, fluidity, and self-healing are excellent candidates for highly stretchable fibers with sensing, actuation, power generation, and interconnection functionalities. However, current LM fibers fabricated by direct injection or surface coating have a limitation in shape programmability. This hinders their applications in functional fibers with tunable electromechanical response and miniaturization. Here, we reported a simple and efficient method to create shape-programmable LM fibers using the phase transition of gallium. Gallium metal wires in the solid state can be easily shaped into a 3D helical structure, and the structure can be preserved after coating the wire with polyurethane and liquifying the metal. The 3D helical LM fiber offered enhanced stretchability with a high breaking strain of 1273% and showed invariable conductance over 283% strain. Moreover, we can reduce the fiber diameter by stretching the fiber during the solidification of polyurethane. We also demonstrated applications of the programmed fibers in self-powered strain sensing, heart rate monitoring, airflow, and humidity sensing. This work provided simple and facile ways toward functional LM fibers, which may facilitate the broad applications of LM fibers in e-skins, wearable computation, soft robots, and smart fabrics.

Data Glove with Self-Compensation Mechanism Based on High-Sensitive Elastic Fiber-Optic Sensor

With the development of virtual reality (VR) interaction technology, data glove has become one of the most popular devices for human-computer interaction. It's valuable to design high-sensitive and flexible sensor for data glove. Therefore, a low-cost data glove based on self-compensating elastic optical fiber sensor with self-calibration function is proposed. The tunable and stretchable elastic fiber was fabricated by a simple, economical and controllable method. The fiber has good flexibility and high stability under stretching, bending and indentation deformation. The optical fibers are installed in the sensor in a U shape with a bending radius of 5 mm. Compared with the straight fiber, the response sensitivity of the U-shaped fiber to deformation is increased by about 7 times at most. The reference optical fiber is connected to the sensor, which effectively improves the stability and accuracy of the sensor system. In addition, the sensors are easy to install so that the data gloves can be customized for different hand shapes. In the gesture capture test, it can respond quickly and guide the manipulator to track the gesture. This responsive and stable data glove has broad development potential in motion monitoring, telemedicine and human-computer interaction.

A Self-repairing transparent film with reprocessable, ultra-high strength and outstanding elasticity based on interlocking hydrogen bonds and reversible topological networks

Achieving robust, high elasticity, transparency, self-repairing, reprocessability and durability simultaneously remains a huge challenge. In this work, we propose a simple strategy to prepare an ultra-high strength, outstanding elasticity, self-repairing and reprocessable poly (thiourethane-urea) (PTUU) film based on interlocking hydrogen bonds (IHBs) and reversible topological networks. The IHBs between its main chains make it have ultra-high tensile strength (61.6 MPa) and good scratch resistance. It is the highest tensile strength ever recorded for crosslinked self-repairing materials at medium temperature thus far. The synergistic effect of IHBs and topological networks makes it high elasticity and can repair more than 90 % of the mechanical strength. Rearrangement of reversible topology network at high temperature endows PTUU with reprocessability, and the mechanical strength remains more than 85 % after reprocessing for three times. In addition, PTUU films have high transmittance (96.6 %, 0.5 mm), low haze, high refractive index and excellent durability, which have broad application prospects in transparent protective materials, optical lenses, stretchable fibers, wearable electronic devices and other fields.

Conductance-stable and integrated helical fiber electrodes toward stretchy energy storage and self-powered sensing utilization

Highly conductive and stretchable fibers are of great significance for wearable applications. Practical applications usually require high robustness and repeatability for these electronics under various mechanical deformations, which is a contradiction for most of existing strain-sensitive fibers conductors. In this work, core–shell hydrogel fiber with adjustable three-dimensional (3D) helical structure was fabricated, in which Ti3C2Tx (MXene)/poly(3,4-ethylenedioxythiophene) (PEDOT) were modified onto the surface of helical sodium alginate/polyacrylic acid (SA/PAA) hydrogel fibers via the combination of in situ polymerization and electrostatic assembly. The hybrid fiber possess a insensitive conductance (<5% resistance change) under various deformation, including stretching (0–800 %), bending (0-180°), pressuring and twisting, attributed to both the double tortuous conductive network and pre-strain release from helical structure. Moreover, conductance-stable helical fibers could be appropriately assembled into coaxial energy fibers and integrated into fabric, both acting as strain-insensitive energy storage device and self-powered wearable sensor.

Water-Processable, Stretchable, and Ion-Conducting Coacervate Fibers from Keratin Associations with Polyelectrolytes.

Keratin is one of the most abundant biopolymers, produced on a scale of millions of tons per year but often simply discarded as waste. Due to its abundance, biocompatibility, and excellent mechanical properties, there is an extremely high interest in developing protocols for the recycling of keratin and its conversion into protein-based materials. In this work, we describe a novel protocol for the conversion of keratin from wool into hybrid fibers. Our protocol uses a synthetic polyanion, which undergoes complex coacervation with keratin, leading to a viscous liquid phase that can be used directly as a dope for dry-spinning. The use of polyelectrolyte complexation allows us to use all of the extracted keratin, unlike previous works that were limited to the fraction with the highest molecular weight. The fibers prepared by this protocol show excellent mechanical properties, humidity responsiveness, and ion conductivity, which makes them promising candidates for applications as a strain sensor.

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.

Thermoplastic and Electrically Conductive Fibers for Highly Stretchable and Sensitive Strain Sensors

Stretchable and conductive fibers have attracted immense interest in the fields of electronic skin, smart textiles, and environmental monitoring due to their inherited unique characteristics. Although various types of stretchable fibers have been investigated, the complicated fabrication and high cost of the specifically designed fibers have greatly hindered the broad applications of the sensors. This work reports the use of thermoplastic polyurethane (TPU) integrated with a semiliquid metal (SLM) to fabricate SLM-TPU fiber (namely, STF) through traditional melt extrusion. The interaction between SLM and TPU enables STF to be highly sensitive (gauge factor (GF): 177–240) and stretchable (strain: 421%) resistive sensor. Besides, this work discovers that TPU could act as an effective adhesive to conveniently construct different structures from the fibers, such as hexagonal-prism, double-helix and mesh textures. These diverse structures enhance the tensile strength and strain of STF. In addition, the phenomenal sensitivity and stretchability make the STF a rapid-response strain sensor with the ability to monitor human motion.

3D stretchable and self-encapsulated multimaterial triboelectric fibers.

A robust power device for wearable technologies and soft electronics must feature good encapsulation, high deformability, and reliable electrical outputs. Despite substantial progress in materials and architectures for two-dimensional (2D) planar power configurations, fiber-based systems remain limited to relatively simple configurations and low performance due to challenges in processing methods. Here, we extend complex 2D triboelectric nanogenerator configurations to 3D fiber formats based on scalable thermal processing of water-resistant thermoplastic elastomers and composites. We perform mechanical analysis using finite element modeling to understand the fiber's deformation and the level of control and engineering on its mechanical behavior and thus to guide its dimensional designs for enhanced electrical performance. With microtexture patterned functional surfaces, the resulting fibers can reliably produce state-of-the-art electrical outputs from various mechanical deformations, even under harsh conditions. These mechanical and electrical attributes allow their integration with large and stretchable surfaces for electricity generation of hundreds of microamperes.

A highly stretchable and conductive continuous composite filament with buckled polypyrrole coating for stretchy electronic textiles

Highly stretchable and conductive fibers as crucial components for stretchy electronic textiles have developed rapidly in recent years, benefiting from the design of stretchable structures. However, routes toward continuous production via simpler fabrication processes remain a huge challenge that has greatly limited its widespread application. In this work, we reported an intrinsically stretchable multifilament with both highly stretchable and conductive (537 S m−1 under 100 % strain) polypyrrole (PPy) coating enhanced by sodium sulfosalicylate (NaSSA) as a dopant. Based on this, a post-drawing method was further proposed to continuously fabricate stretchable conductors with PPy buckling on surface. The PU multifilament with buckle PPy coating (PU@bPPy) exhibited a high and ultra-stable conductance, showing initial conductivity at 529 S m−1 and only 3.5 % change in resistance after > 6500 stretching cycles at 50 % strain. Moreover, the PU@bPPy could be easily integrated into electronic textiles as stretchable electronic circuits and stretchable joule heaters.

Maple Leaf Inspired Conductive Fiber with Hierarchical Wrinkles for Highly Stretchable and Integratable Electronics.

Stretchable and durable conductors are significant to the development of wearable devices, robots, human-machine interfaces, and other artificial intelligence products. However, the desirable strain-insensitive conductivity and low hysteresis are restricted by the failure of stretchable structures and mismatch of mechanical properties (rigid conductive layer and elastic core substrate) under large deformation. Here, based on the principles of fractal geometry, a stretchable conductive fiber with hierarchical wrinkles inspired by the unique shape of the maple leaf was fabricated by combining surface modification, interfacial polymerization, and improved prestrain finishing methods to break through this dilemma. The shape and size of wrinkles predicted by buckling analysis via the finite element method fit well with that of actual wrinkles (30-80 μm of macro wrinkles and 4-6 μm of micro wrinkles) on the fabricated fiber. Such hierarchically wrinkled conductive fiber (HWCF) exhibited not only excellent strain-insensitive conductivity denoted by the relative resistance change ΔR/R0 = 0.66 with R0 the original resistance and ΔR the change of resistance after the concrete strain reaching up to 600%, but also low hysteresis (0.04) calculated by the difference in area between stretching and releasing curve of the ΔR/R0 strain under 300% strain and long-term durability (>1000 stretching-releasing cycles). Furthermore, the elastic conductive fiber with such a bionic structure design can be applied as highly stretchable electrical circuits for illumination and monitors for the human motion under large strains through tiny and rapid resistance changes as well. Such a smart biomimetic material holds great prospects in the field of stretchable electronics.

Highly elastic halochromic fibers capable of reversible sensing of acidic/basic vapor for use in wearable textiles

Halochromic sensors, which allow users to visually recognize exposure to acid/base chemicals that are harmful to the human body, are routinely used in a wide range of industries, such as pharmaceuticals, biotechnology, cosmetics, and environmental/human monitoring systems. In this study, halochromic fibers that operate stably, even when exposed to rain or sweat and repeated stretching–releasing, were investigated. While the halochromic mesoporous silica was synthesized using tetraethylorthosilicate and cetyltrimethylammonium bromide, methyl yellow (MY) and bromothymol blue (BTB) as halochromic dyes were added so that MY and BTB were chemically or physically immobilized on the siloxane network structure of the halochromic mesoporous silica. Using the swelling and shrinking properties of the polymer, the halochromic mesoporous silica was embedded in a highly elastic spandex fiber composed of multiple strands. Because of the strong ionic and hydrogen bonding between the dye and the silica matrix, the dyes can be immobilized even in an aqueous solution without the leaching of the dyes. The stretchable halochromic fiber reversibly changed its color even after repeated exposure to acidic/basic conditions five times and could sense acid/base concentrations in the range of 0.5–10 wt %. In addition, because the halochromic mesoporous silica is tightly adhered between the stands of spandex fibers, stable color conversion properties were maintained even after stretching to 150% of the fibers and repeated 100 times. Because the halochromic fiber can be applied to lab coats, work clothes, and gloves, it is expected to be used as a wearable colorimetric sensor for daily life and industrial applications.

Interfacial modification strategy for the fabrication of high performance fiber-based strain sensors

Lightweight, stretchable, and wearable fiber strain sensors have recently been widely studied for the development of health monitoring systems, human-machine interfaces, and wearable devices. The interface interaction between the stretchable substrate and conducting materials plays a vital role in the performance of the fiber-based strain sensors. In this work, a scalable strategy using elastic yarn as a flexible substrate coated with a one-dimensional (1D) multiwalled carbon nanotube (MWCNT) and two-dimensional (2D) MXene (Ti3C2Tx) mixed conductive layer was presented. The introduction of ultra-thin polyurethane (PU) bridge layer into the sensing system greatly improved the interfacial adhesion between the yarn and conductive layer. Therefore, the sensors obtained significantly enhanced performance, which exhibited the superstretchability up to 300% without evidently irreversible damaging the intrinsic conductive pathways (the maximum elongation reached 1218%), high sensitivity (maximum gauge factor is approximately 441.68 at 210%–300%), fast response time (about 70 ms), and excellent stability (low fatigue properties over 1500 stretch-release cycles). Furthermore, the fabricated fiber strain sensors were used to access the relevant physiological signals, including finger and joint movements, face gestures, and sitting posture detection. Such high mechanical performance fiber-based electronics can serve as the basis for future multifunctional smart wearable sensors for abundant existing and emerging applications.

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.

Scalable, stretchable and washable triboelectric fibers for self-powering human-machine interaction and cardiopulmonary resuscitation training

Flexible and stretchable fiber-shaped triboelectric nanogenerators (FTENGs) have been extensively investigated in wearable electronics due to their ability to harvest human-body mechanical energy and serve as self-powered sensing systems. However, developing a facial and scalable fabrication method for highly flexible and comfortable FTENGs remains a formidable challenge. Here, a scalable, flexible and washable coaxially structured FTENGs is developed, which possess excellent mechanical stretchability, weave-ability and electrical output performance. The instantaneous power density of FTENG fabrics with an effective area of 32 cm2 can reach as high as 0.957 W m-2 under an external load resistance of 10 MΩ, which is superior to the vast majority of reported work. As self-powered sensors, FTENGs can harvest human motion energy for the detection of body physiological signals and human-machine interactions. Importantly, a wearable cardiopulmonary resuscitation training system is developed based on the FTENGs, which can evaluate the quality of chest compressions, including compression rate, depth, chest compression leaning and chest recoil condition. All these advantages of FTENGs are expected to broadly benefit the development of medical assistance training.

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.

Experimental Detection of Particle Structures Detachment from a Stretchable Single Fiber during Multiple Consecutive Stretching Cycles

The deposited particulate material within a fibrous filter affects the pressure drop which develops through three different stages. The implementation of a time-adjustable matrix is intended to cause detachment of particle structures from fibers within the upstream layers at low flow velocities. The deposited particle structures are transported further within the filter and clear up void space for an extension of filter service life. As in previous studies observed fiber stretching initiate cracks and following detachment of particle structures with a simultaneously applied airflow. For complete detachment of the particle structure, five consecutive stretching cycles are performed in this study. The elongation velocity, the flow velocity and the particle loading are varied. Using an image analysis technique and a laser-light measurement technique simultaneously, the cumulative fraction of detached particle structures and the size of detached particle structures are determined. A high initial particle loading on the fiber induces early detachment of larger structures from the fiber. The size of detached structures is increased by the increase of the elongation velocity. The mean value remains almost constant whether the elongation velocity or superficial velocity are increased. For small initial structures on the fiber, a decrease in superficial velocity causes detachment of larger particle fragments.

The stretchable carbon black-based strain fiber with a remarkable linearity in a wide sensing range

ABSTRACT Ascribed to its wide sensing range, high sensitivity, and low stiffness to match target objects with complex 3D shapes, the stretchable strain sensor has shown its promising applications in various fields, ranging from healthcare, bodynet, and intelligent traffic system, to the robotic system. This paper presents a low-cost and straightforward fabrication technology for the stretchable strain fiber with the combined attributes of a wide sensing range, exceptional linearity, and high durability. The hybrid composite consisting of carbon black and silicone is utilized as the functional material to respond to the external mechanical deformation due to the piezoresistive effect. To address the remarkable hysteresis of the CB-silicone composites, the latex tubes with excellent mechanical robustness and a considerable accessible tensile strain are introduced as the outer supporting components. After injecting the conductive CB-silicone composite into these tubes, the stretchable strain fibers are successfully prepared. Notably, the stretchable strain sensor exhibits linearity (R2 = 0.9854) in a wide sensing range (0–400%) and remarkable durability even after the 2500 cycles under 100% tension. Additionally, the potential of this stretchable strain fiber as the wearable strain sensor and the real-time feedback is demonstrated by detecting the body motion and the expansion devices.

Coordination and hydrogen bond-coadjusted highly stretchable wet-spun poly(acrylic acid) fiber and its stable activity as Fenton catalyst

High stretching is an effective route to attain high performance fiber. Therefore, the stretchability of wet-spun poly(acrylic acid) (PAA) fiber is important for the preparation of high performance PAA fiber by stretching. A combination of coordination and hydrogen bonding was synergistically used to prepare highly stretchable wet-spun PAA fibers, and high stretching was subsequently carried out to induce the production of molecular orientation and fibrillar crystals, which can remarkably enhance the strength of resulting fiber. The breaking strength of stretched fiber reached up to 1.631cN/dtex, increasing by 2813% compared to that of unstretched fiber. Moreover, high stretching was used to thin the resulting fiber and promote the transformation of PAA chains from coiled to extensional conformation, so that the carboxyl groups wrapped by coiled PAA chains were exposed to the environment. When the highly stretched fiber was used to decolorize methylene blue (MB) aqueous solution, the exposed carboxyl groups can quickly re-coordinate with the iron ions eluted by MB aqueous solution to minimize the loss of iron ions. The measurement results showed that the average concentration of eluted iron ions was only 3.20 mg/L during 40 operation cycles for the highly stretched fiber, decreasing by 64.0% compared to that of unstretched fiber. Due to low iron ion leaching-out, the highly stretched fiber showed superstable activity in catalyzing H2O2 to oxidatively decolorize MB. The research results revealed that the obtained fiber can decolorize more than 90% MB within 3 min during 40 cycles without showing any obvious attenuation in decolorization efficiency and decolorization rate. In this case, the Fenton catalysts reported by literature are scarcely comparable to the prepared fiber in many aspects. Therefore, the fiber prepared in this work can be expected to show great potential for application in the field of dye wastewater treatment.