Stretchable Fibers Research Articles

Wet-spinning fabrication of stretchable multicolor fluorescent fibers augmented with dual-state emissive dyes

Flexible luminous fibers have attracted wide attention in the field of functional and smart textiles. In this work, stretchable multicolor fluorescent fibers were successfully prepared by wet-spinning using thermoplastic polyurethane (TPU) and the boron ketoimine fluorophores (TPA-BKI dyes). Due to the donor (D)-acceptor (A) push-pull electronic system and highly twisted triphenylamine (TPA) skeleton, TPA-BKI dyes exhibited bright emission in both solution and solid states. Meanwhile, the polymer chains further improved the emission efficiency of TPA-BKI dyes in TPU matrix by avoiding close contact between dye molecules, as well as preventing intramolecular rotations in the excited states. Wet-spinning can be used for large-scale and continuous preparation of fluorescent fibers. The TPA-BKI/TPU fibers showed excellent flexibility, high mechanical strength, and bright multicolor fluorescent emission (green, yellow, and red, respectively) when the dye content was as low as 0.1 wt%. Overall, the feasibility of large-scale preparation of fluorescent fibers and their excellent properties, such as flexibility, multicolor fluorescence, and mechanical stability, make them suitable for potential applications, including clothing displays, fashion designs, security, and anti-counterfeiting.

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.

Development of a Highly Sensitive and Stretchable Charge-Transfer Fiber Strain Sensor for Wearable Applications.

Wearable electronics have significantly advanced the development of highly stretchable strain sensors, which are essential for applications such as health monitoring, human-machine interfaces, and energy harvesting. Fiber-based sensors and polymeric materials are promising due to their flexibility and tunable properties, although balancing sensitivity and stretchability remains a challenge. This study introduces a novel composite strain sensor that combines poly(3-hexylthiophene) and tetrafluoro-tetracyanoquinodimethane to form a charge-transfer complex (CTC) with carbon nanotubes (CNTs) on a styrene-butadiene-styrene substrate. The CTC improves conductivity through effective charge transfer, while CNTs provide mechanical reinforcement and maintain conductive paths, preventing cracks under large strains. Purposefully introduced wrinkles in the structure enhance the detection of small strains. The sensor demonstrated a broad strain-sensing range from 0.01 to 200%, exhibiting high sensitivity to both minor and major deformations. Mechanical tests confirmed strong stress-strain performance, and electrical tests indicated significant conductivity improvements with CNT integration. These results highlight the potential of the sensor for applications in health monitoring, human-machine interfaces, and energy harvesting, effectively mimicking the tactile sensing abilities of human skin.

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.

Stretchable and Self-Powered Mechanoluminescent Triboelectric Nanogenerator Fibers toward Wearable Amphibious Electro-Optical Sensor Textiles.

Flexible electro-optical dual-mode sensor fibers with capability of the perceiving and converting mechanical stimuli into digital-visual signals show good prospects in smart human-machine interaction interfaces. However, heavy mass, low stretchability, and lack of non-contact sensing function seriously impede their practical application in wearable electronics. To address these challenges, a stretchable and self-powered mechanoluminescent triboelectric nanogenerator fiber (MLTENGF) based on lightweight carbon nanotube fiber is successfully constructed. Taking advantage of their mechanoluminescent-triboelectric synergistic effect, the well-designed MLTENGF delivers an excellent enhancement electrical signal of 200% and an evident optical signal whether on land or underwater. More encouragingly, the MLTENGF device possesses outstanding stability with almost unchanged sensitivity after stretching for 200%. Furthermore, an extraordinary non-contact sensing capability with a detection distance of up to 35cm is achieved for the MLTENGF. As application demonstrations, MLTENGFs can be used for home security monitoring, intelligent zither, traffic vehicle collision avoidance, and underwater communication. Thus, this work accelerates the development of wearable electro-optical textile electronics for smart human-machine interaction interfaces.

Durable Flexible Conductive Fiber Based on Cross-Linking Network Tannic Acid/Polypyrrole for Wearable Thermotherapy Monitoring System.

Intelligent wearable textiles have garnered attention and advancement, particularly in the realms of thermotherapy and health monitoring. As a critical component of intelligent wearable textiles, conductive fibers are expected to have long-term stable and durable conductivity. In this work, a highly stretchable and conductive fiber based on tannic acid/polypyrrole was developed. The conductive network was formed by doping TA into PPy, resulting in enhanced stretchability of PPy on the surface of PU. TA also improves the interface interaction between PPy and PU to gain more firm attachment of PPy, which achieves high conductivity (0.89 ± 0.23 S/cm) and durability. Furthermore, the stretchable conductive fiber also exhibited intelligent responses to electricity, light, and deformation. They can serve as heat sources under the action of electricity and light (temperature was raised to 42 °C under 4 V and 54 °C under solar radiation stimuli) and can also monitor the movements of humans, making them potential applications in thermotherapy textiles and intelligent sensing equipment. A PU/TA/PPy-based all-in-one smart wearable system was fabricated using textile molding technology capable of all-weather thermal therapy and motion detection. This fiber fabrication technology and integrated system offer insights for the future development of smart wearable devices.

Multifunctional ultraelastic helical conductive yarn for motion detection and human-machine interaction

Featured with intrinsic lightweight, great flexibility, and easy integration into functional textiles or devices, the stretchable conductive fiber has attracted much attention in the realm of wearable electronics. However, the conductive fibers encounter a troublesome “trade-off” between high conductivity and large elasticity under large deformation, which restricts their widespread applications. Herein, we designed a multifunctional highly elastic helical conductive yarn (HCY) by electrospinning polyurethane (PU) nanofibers, polydopamine (PDA)-assisted silver nanoparticles (AgNPs) deposition and over-twisting. The introduction of a PDA mediated layer fosters strong bond between the conductive AgNPs and the elastic PU nanofibers matrix, showcasing robust structural stability and electrical performance. The hierarchically interlocked conductive structure confers high electrical conductivity to the stretchable HCY, enabling it to withstand large mechanical deformation, which achieves good recoverability within a range of 700 %, great durability (40000 times at deformation of 200 %) and maximum conductive tensile elongation up to 1200 %. Furthermore, the HCY also features excellent Joule-heating ability, great antibacterial performance, and functions as a rapid-response strain sensor (GFmax = 9.82), which is ideal for detecting human motion and enhancing human–machine interactions. This work provides a new path for developing advanced stretchable conductive materials, which is of great significance for versatile ultraelastic wearable electronic devices.

Coaxially spinning spiral coils into concentric microtubes to synchronize motion and temperature sensing for stretchable and wearable device

Wearable electronical sensors with the combination of multi-mode sensing, stretchability and stability have long been in pursuit for various applications, such as the strain and temperature sensing for health assessment and disease diagnosis. To design endurable dual-mode sensor without signal interference, in this study, a coaxial wet spinning process were suggested to spin helical fibers into concentric double-layer microtubes to synchronize motion and temperature sensing with negligible signal interference. The inner helical fiber showed a high temperature-dependent ionic conductivity for the sensitivity of 5.76 % °C−1 and detection limit of 0.1 °C. Its helical geometry ensured large stretchability and minimal strain-induced interference. The outer coating shell could serve as the strain sensor with a high gauge factor of 11.36–1512 (up to 300 % strain) and response time of 120 ms. When filling the microtubes with polydimethylsiloxane, the multi-mode sensos could stay stable sensing abilities up to 104 stretching-release cycles. Thus, this study not only offers a coaxial spinning approach for production of stretchable multicomponent fibers, but also shows an unprecedented alternative of dual-mode sensor for healthcare, rehabilitation, and sleep monitoring.

Highly sensitive and stretchable fiber strain sensors based on ITO NPs/CNTs composite

Flexible and multifunctional sensors are in demand in various fields, but achieving excellent sensitivity and an extensive operational range poses a challenge. Here, we developed a flexible strain sensor using a cost-effective dip-coating method, incorporating microcracked synergistic indium tin oxide nanoparticles (ITO NPs) and carbon nanotubes (CNTs) in a conductive layer. Utilizing an elastic rubber core string as the stretchable substrate and Thermoplastic polyurethane (TPU) as an interfacial modifier, we established connectivity between the substrate and conductive layer. After encapsulation with polydimethylsiloxane, the ITO NPs/CNTs/rubber fiber (ICRF) strain sensor was fabricated. This sensor demonstrates a broad sensing range (0 ∼ 300 %), remarkable sensitivity (GF=1033.57), swift response/recovery times (174.55 ms/180.27 ms), and exceptional durability and stability (>2000 cycles). Moreover, it proves effective for human motion detection, underscoring its potential in flexible and wearable devices. Finally, precise responses of the mechanical claw’s posture and grasping demonstrate its potential applications across multiple fields.

Highly Stretchable Thermoelectric Fiber with Embedded Copper(I) Iodide Nanoparticles for a Multimodal Temperature, Strain, and Pressure Sensor in Wearable Electronics

AbstractThermoelectric (TE) fibers have excellent potential for multimodal sensor, which can detect mechanical and thermal stimuli, used in advanced wearable electronics for personalized healthcare system. However, previously reported TE fibers have limitations for use in wearable multimodal sensors due to the following reasons: 1) TE fibers composed of carbon or organic materials have low TE performance to detect thermal variations effectively; 2) TE fibers composed of rigid inorganic materials are not stretchable, limiting their ability to detect mechanical deformation. Herein, the first stretchable TE fiber‐based multimodal sensor is developed using copper(I) iodide (CuI), an inorganic TE material, through a novel fabrication method. The dense CuI nanoparticle networks embedded in the fiber allow the sensor to achieve excellent stretchability (maximum tensile strain of ≈835%) and superior TE performance (Seebeck coefficient of ≈203.6 µV K−1) simultaneously. The sensor exhibits remarkable performances in strain sensing (gauge factor of ≈3.89 with tensile strain range of ≈200%) and pressure sensing (pressure resolution of ≈250 Pa with pressure range of ≈84 kPa). Additionally, the sensor enables independent and simultaneous temperature change, tensile strain, and pressure sensing by measuring distinct parameters. It is seamlessly integrated into a smart glove, demonstrating its practical application in wearable technology.

Discrete Element Method Simulation of Particulate Material Fracture Behavior on a Stretchable Single Filter Fiber with Additional Gas Flow

This study presents a comprehensive discrete element method (DEM) simulation approach for the stretching of a filter fiber with a separated polydisperse particle structure on top. For a realistic interaction between the fiber surface and the particles, the original surface of the polymer fiber was projected onto the surface of the fiber cylinder using surface imaging technologies (atomic force microscopy (AFM) and white-light interferometry). In addition, the adhesive forces between particle–fiber and particle–particle contacts were calibrated in the DEM domain using values from self-conducted AFM measurements. Fiber stretching was implemented by the linear motion of small periodic fiber elements. Discretization problems were resolved through studying the stretching of a fiber segment at the size of 8 mm. A critical fiber element length was discovered to be ≈100 μm for minimizing discretization dependencies during the cracking of the particle structure. The number and density of particle–particle contacts within the particle loading on the fiber were obtained at two different elongation rates. Effects such as densification of the particulate structure and increased detachment due to additional air flow were demonstrated.

Strain‐Insensitive Pre‐Stretch‐Stabilized Polymer/Gold Hybrid Electrodes for Electrochemiluminescent Devices

AbstractThe quest for stretchable properties is at the forefront of research dedicated to on‐skin light–emitting devices. Inspired by the natural wonders of bioluminescence, electrochemiluminescent devices (ECLDs) are distinguished by straightforward design and reduced operating voltage, marking a departure from traditional current‐driven electroluminescent devices (ACELDs). The primary challenge of fully‐stretchable ECLDs lies in crafting electrodes that simultaneously satisfy the demands for conductivity, transparency, stretchability, oxidation resistance, and interface stability. This research introduces a groundbreaking wrinkled polymer‐gold composite electrode. It extends to 50% stretchability, offers outstanding conductivity at 10 Ω sq−1, achieves transparency above 60%, and withstands over 10 000 stretching cycles. Employing this material, alongside stretchable electrospinning fiber luminescent layers, enabled the creation of fully‐stretchable ECLDs. These devices not only shine brightly at 30 Cd m−2 but also retain more than 90% of luminosity when stretched up to 50%. Furthermore, this work has engineered stretchable devices featuring singular patterns and multi‐dot arrays. They exhibit consistent luminescent output under bending, twisting, and stretching when applied to skin. These findings not only highlight the potential of polymer‐gold composite electrodes in overcoming challenges faced by stretchable electronic devices but also provide new ideas for wearable technology that seamlessly integrates with human body.

A Review of Wearable Optical Fiber Sensors for Rehabilitation Monitoring.

As the global aging population increases, the demand for rehabilitation of elderly hand conditions has attracted increased attention in the field of wearable sensors. Owing to their distinctive anti-electromagnetic interference properties, high sensitivity, and excellent biocompatibility, optical fiber sensors exhibit substantial potential for applications in monitoring finger movements, physiological parameters, and tactile responses during rehabilitation. This review provides a brief introduction to the principles and technologies of various fiber sensors, including the Fiber Bragg Grating sensor, self-luminescent stretchable optical fiber sensor, and optic fiber Fabry-Perot sensor. In addition, specific applications are discussed within the rehabilitation field. Furthermore, challenges inherent to current optical fiber sensing technology, such as enhancing the sensitivity and flexibility of the sensors, reducing their cost, and refining system integration, are also addressed. Due to technological developments and greater efforts by researchers, it is likely that wearable optical fiber sensors will become commercially available and extensively utilized for rehabilitation.

Polarization‐Induced Mechanically Socketed Ultra‐Stretchable and Breathable Textile‐Based Nanogenerator and Pressure Sensor

AbstractTextile‐based wearable triboelectric nanogenerators (TENGs) have emerged as viable power sources for wearable electronics. However, it is still a daunting challenge to realize a high‐performing textile‐based nanogenerator without compromising its intrinsic textile‐like properties, such as stretchability, breathability, and conformability. The above challenge is addressed by fabricating a record high‐performing wearable, breathable and stretchable nanogenerator based on polarization‐induced ultra‐stretchable EVA/Nylon‐11 micro/nano‐fibers (1250%) as the triboelectric positive layer and polarization‐induced ultra‐stretchable EVA/PVDF/BA2CsAgBiBr7 micro/nano‐fibers (1480%) as the triboelectric negative layer. The excellent stretchability, breathability (1.15 Kgm−2d−1) and high energy‐harvesting performance (650 V, 19.5 µAcm−2) are attributed to the mechanically‐socketed structure of the aligned stretchable EVA microfibers with the polarized nanofibers, thus providing a universal framework to fabricate stretchable piezoelectric fibers. Compositional engineering and polarization‐induced surface charges coupled with triboelectric‐induced surface charges enabled enhanced performance compared to other wearable stretchable textile‐based nanogenerators. Additionally, it is utilized as a stretchable self‐powered pressure sensor with an ultra‐wide pressure sensing range (0.05–500 kPa) and high sensitivity (2.5 VkPa−1) even under deformations. To the best of the knowledge, PI‐STENG stands out amongst various stretchable self‐powered pressure sensors in terms of pressure sensing range and stretchability. The PI‐STENG is demonstrated as a machine learning‐enabled intellisensor for workforce safety monitoring.

Stretchable fiber strain sensors for wearable biomonitoring.

Stretchable fiber strain sensors for wearable biomonitoring.

Stretchable Polymer Optical Fiber With an Unusual Relationship Between Optical Loss and Elongation

Stretchable Polymer Optical Fiber With an Unusual Relationship Between Optical Loss and Elongation

In-situ forming ultra-mechanically sensitive materials for high-sensitivity stretchable fiber strain sensors.

Fiber electronics with flexible and weavable features can be easily integrated into textiles for wearable applications. However, due to small sizes and curved surfaces of fiber materials, it remains challenging to load robust active layers, thus hindering production of high-sensitivity fiber strain sensors. Herein, functional sensing materials are firmly anchored on the fiber surface in-situ through a hydrolytic condensation process. The anchoring sensing layer with robust interfacial adhesion is ultra-mechanically sensitive, which significantly improves the sensitivity of strain sensors due to the easy generation of microcracks during stretching. The resulting stretchable fiber sensors simultaneously possess an ultra-low strain detection limit of 0.05%, a high stretchability of 100%, and a high gauge factor of 433.6, giving 254-folds enhancement in sensitivity. Additionally, these fiber sensors are soft and lightweight, enabling them to be attached onto skin or woven into clothes for recording physiological signals, e.g. pulse wave velocity has been effectively obtained by them. As a demonstration, a fiber sensor-based wearable smart healthcare system is designed to monitor and transmit health status for timely intervention. This work presents an effective strategy for developing high-performance fiber strain sensors as well as other stretchable electronic devices.

A highly sensitive stretchable constraint fiber mat sensor with tailored near-zero Poisson’s ratio for very early stage of battery over charge/overdischarge monitoring

Battery state monitoring is crucial for safe operation and efficient management of lithium-ion battery (LIB) systems, but early stage of timely and accurate diagnosis remains challenging. Herein, we propose to utilize a highly sensitive stretchable strain sensor to in-situ monitor the slight strain variation of cells during charge and discharge, through which the state of the battery can be accurately reflected. The high sensing capability is realized by tailoring the Poisson’s ratio of low-modulus conductive fiber mats through a facile constraint manner. The non-uniform strain distribution together with the near-zero Poisson’s ratio synergistically result in the superior sensing performance, including ultralow strain detection limit (0.006%), high strain sensitivity particularly under small strains (gauge factor of 116.1 between 0 and 2% strain), and high strain resolution under large deformations. When being practically utilized for LIB monitoring, the constraint fiber mat sensor can produce instant resistance response reflecting the cell capacity, and offer timely warning signal once the cell is overcharged or overdischarged. The developed stretchable strain sensor possesses comprehensive advantages of low mechanical constraint, tailorable small size, easy integration and conformality to cells, and little temperature interference, which would serve as a promising candidate for future battery state analysis and safety monitoring.

Coaxially spinning stretchable zin-ion battery fiber with waterproof and scissorability

Wearable energy storage with super mechanic flexibility, stretchability and safety has been in pursuit for smart flexible textiles. Fiber batteries, though having their superiority in spinnability, knittability and adaptability for breathable textiles with comparison to planar batteries, were normally produced with complicated procedures. To simplify the production process, in this study we showed that stretchable and scissorable Zinc-ion battery fibers could be spun through a dual-core spinning head with double concentric sheathes, by combining a one-step coaxial wet-spinning process and an in-situ photo-polymerization process. The resultant fibers showed super stretchability up to 500 % strain. The presence of outer protection layer also offered super abrasion resistance and endurability to water and stress. Besides the spinnability and knittability into fabric, the battery fibers also maintained their functionality even after being cut into short segments. Thus, this study may not only offer a platform of one-step coaxial wet spinning process to produce battery fibers, but also offer an endurable energy-storage solution applicable in various wearable devices.

A Highly Sensitive and Stretchable Core-Shell Fiber Sensor for Gesture Recognition and Surface Pressure Distribution Monitoring.

This work reports a highly-strain flexible fiber sensor with a core-shell structure utilizes a unique swelling diffusion technique to infiltrate carbon nanotubes (CNTs) into the surface layer of Ecoflex fibers. Compared with traditional blended Ecoflex/CNTs fibers, this manufacturing process ensures that the sensor maintains the mechanical properties (923% strain) of the Ecoflex fiber while also improving sensitivity (gauge factor is up to 3716). By adjusting the penetration time during fabrication, the sensor can be customized for different uses. As an application demonstration, the fiber sensor is integrated into the glove to develop a wearable gesture language recognition system with high sensitivity and precision. Additionally, the authors successfully monitor the pressure distribution on the curved surface of a soccer ball by winding the fiber sensor along the ball's surface.