Soft Fibers Research Articles

4.8-μm CO-filled hollow-core silica fiber light source

Mid-infrared (MIR) fiber lasers are important for a wide range of applications in sensing, spectroscopy, imaging, defense, and security. Some progress has been made in the research of MIR fiber lasers based on soft glass fibers, however, the emission range of rare-earth ions and the robustness of the host materials are still a major challenge for MIR fiber lasers. The large number of gases provide a variety of optical transitions in the MIR band. When combined with recent advances in low-loss hollow-core fiber (HCF), there is a great opportunity for gas-filled fiber lasers to further extend the radiation to the MIR region. Here, a 4.8-μm CO-filled silica-based HCF laser is reported for the first time. This is enabled by an in-house manufactured broadband low-loss HCF with a measured loss of 1.81 dB/m at 4.8 μm. A maximum MIR output power of 46 mW and a tuning range of 180 nm (from 4644 to 4824 nm) are obtained by using an advanced 2.33-μm narrow-linewidth fiber laser. This demonstration represents the longest-wavelength silica-based fiber laser to date, while the absorption loss of bulk silica at 4824 nm is up to 13, 000 dB/m. Further wavelength expansion could be achieved by changing the pump absorption line and optimizing the laser structure.

Tribological properties of perfluoropolymer fiber filled carbon fiber/polyphenylene sulfide composites: Effect of in‐situ fibrillated fiber or split fiber

AbstractIn this study, carbon fiber (CF) filled polyphenylene sulfide (PPS) composites are lubricated with perfluoropolymer (PFP) fiber by melt‐blending. The effect of double fibers (CF‐PFP fibers) on the tribological properties of PPS composites has been carefully investigated and correlated under various sliding conditions. The results indicated that the tribological performance of PPS composites with double fibers is better than that of the composites with a single fiber, especially under severe conditions. Mechanism exploration suggests that a double‐fiber hybrid structure between a hard CF and a soft PFP fiber could tightly entrap the CF by fibril entanglement, thus preventing the CF from being stripped out of the matrix under the steel ring shearing force. Under optimized conditions, the average friction coefficient of composites with PFP fiber is only about 0.1 at 300 N load under 200 rpm, even lower than half of the average friction coefficient of the composites with PTFE powder under the same condition. Notably, compared to commercial split PFP fibers, the in‐situ formed PFP fibers with more uniform distribution significantly improve the tribological properties. This work open up a novel perspective for improving the tribological performance of composites by systematically regulating the microstructure of self‐lubricating fibrous additives.Highlights PFA is subject to in‐situ fibrillation during melt blending. Fibrous PFP effectively improves the tribological properties of PPS/CF composites. The in‐situ formed PFP fiber contributes to better tribological properties. The double‐fiber hybrid structure prevents the CF from being sheared out. The number of processing cycles affects the tribological properties.

A Soft-Fiber Bioelectronic Device with Axon-Like Architecture Enables Reliable Neural Recording In Vivo under Vigorous Activities.

Implantable neural devices that record neurons in various states, including static states, light activities such as walking, and vigorous activities such as running, offer opportunities for understanding brain functions and dysfunctions. However, recording neurons under vigorous activities remains a long-standing challenge because it leads to intense brain deformation. Thus, three key requirements are needed simultaneously for neural devices, that is, low modulus, low specific interfacial impedance, and high electrical conductivity, to realize stable device/brain interfaces and high-quality transmission of neural signals. However, they always contradict each other in current material strategies. Here, a soft fiber neural device capable of stably tracking individual neurons in the deep brain of medium-sized animals under vigorous activity is reported. Inspired by the axon architecture, this fiber neural device is constructed with a conductive gel fiber possessing a network-in-liquid structure using conjugated polymers and liquid matrices and then insulated with soft fluorine rubber. This strategy reconciles the contradictions and simultaneously confers the fiber neural device with low modulus (300kPa), low specific impedance (579kΩµm2), and high electrical conductivity (32700Sm-1) - ≈1-3 times higher than hydrogels. Stable single-unit spike tracking in running cats, which promises new opportunities for neuroscience is demonstrated.

An eco-friendly enzymatic treatment to prepare spinnable banana fibers as an alternative to cotton for textile applications

Banana fibers are a sustainable material with natural mechanical strength and antibacterial properties. These fibers are extracted from the large amount of waste produced by banana pseudo stems annually. However, despite their numerous advantages, their stiffness and rough texture impede their full use in the textile. This research investigates the degumming treatment of banana fibers using enzyme combination and chemical methods to achieve spinnable soft banana fibers. An L9 orthogonal array was used in a Taguchi design of the experiment to optimize the process parameters. For enzyme combination degumming, the experimental setup comprised different quantities of hemicellulase, laccase, amylase, and pectinase; for chemical degumming, varied amounts of sodium hydroxide (NaOH) were used. The results indicate that enzyme-based degumming procedures produce better results than chemical treatments. Optimum enzyme combinations for various fiber qualities were found using the Taguchi design of experiments. These combinations included Hemicellulase 5 %, Laccase 5 %, Amylase 3 %, and Hemicellulase 5 %, Laccase 3 %, Pectinase 5 %. Without degrading the cellulose structure, these ideal enzyme combinations produced fibers with lower lignin content and higher cellulose percentages, moisture content, and tenacity values. By determining the most efficient enzyme combinations and their effects on fiber qualities, the study offers sustainable fiber processing methods for textile grade banana fiber.

Recent advances to engineer tough basalt fiber reinforced composites: A review

AbstractBasalt fibers, known as “green materials without pollution in the 21st century”, have gained widespread attention due to its good mechanical properties. Basalt fiber‐based composites have applications in various fields such as construction, transportation, energy, and protection. However, as an inorganic fiber material, basalt fiber is hard and brittle and prone to catastrophic failure, reducing the safety of the material. Therefore, it is important to strengthen the toughness of basalt fiber‐based composites. This paper reviews the contributions made by researchers in recent years to enhance the toughness of basalt fiber reinforced composites. It mainly focuses on four aspects: physical and chemical modification of fibers surface, mixed application of multiple fibers, different textile and 3D printing technology, and design of biomimetic structures. Through these methods, the toughness of basalt fiber‐reinforced composite materials was increased by 10%–90%. In today's advocacy for green industrial development, the research and application of basalt fibers are very important for advancing the process of green development. These contributions can promote the application of basalt fiber in engineering fields.Highlights Basalt fiber is a green material without pollution. Basalt fiber reinforced composites is the key material for engineering field. Strengthening interfacial adhesion can significantly improve the toughness of composites. Basalt fibers can serve as an alternative to glass fibers in composite materials. The hybridization of basalt fibers with soft fibers can effectively enhance the toughness of composites.

A chemo-mechanical constitutive model for muscle activation in bat wing skins.

Birds, bats and insects have evolved unique wing structures to achieve a wide range of flight capabilities. Insects have relatively stiff and passive wings, birds have a complex and hierarchical feathered structure and bats have an articulated skeletal system integrated with a highly stretchable skin. The compliant skin of the wing distinguishes bats from all other flying animals and contributes to bats' remarkable, highly manoeuvrable flight performance and high energetic efficiency. The structural and functional complexity of the bat wing skin is one of the least understood although important elements of the bat flight anatomy. The wing skin has two unusual features: a discrete array of very soft elastin fibres and a discrete array of skeletal muscle fibres. The latter is intriguing because skeletal muscle is typically attached to bone, so the arrangement of intramembranous muscle in soft skin raises questions about its role in flight. In this paper, we develop a multi-scale chemo-mechanical constitutive model for bat wing skin. The chemo-mechanical model links cross-bridge cycling to a structure-based continuum model that describes the active viscoelastic behaviour of the soft anisotropic skin tissue. Continuum models at the tissue length-scale are valuable as they are easily implemented in commercial finite element codes to solve problems involving complex geometries, loading and boundary conditions. The constitutive model presented in this paper will be used in detailed finite element simulations to improve our understanding of the mechanics of bat flight in the context of wing kinematics and aerodynamic performance.

Low-loss nodeless hollow-core anti-resonant soft glass fiber for the 4 µm mid-infrared spectral range

Infrared soft glass hollow-core anti-resonant fibers (HC-ARF) with low loss, excellent mode purity, and robust high-power transmission capabilities have vast potential in mid-infrared high-power laser transmission and biomedical fields. Despite this, the fabrication of these fibers still faces formidable challenges, coupled with an incomplete understanding of the transmission characteristics, thereby amplifying the value of further exploration. In this paper, we fabricate a six-cell nodeless infrared HC-ARF originating from purified sulfide glass, synthesized using a meticulous “stack-and-draw” method and dual-gas-path pressure control method. Notably, we experimentally validate the theoretical performance expectations of this fiber. The fiber exhibits outstanding transmission capabilities and optical transmission quality, characterized by a recorded loss of 0.56 dB/m at 4.79 µm. This is already comparable to traditional step-index sulfide fibers, fully demonstrating its tremendous research value and application potential. Our work has successfully fabricated the lowest loss anti-resonant fiber on record in the mid-infrared field, propelling the development of sulfide HC-ARFs into a new phase and laying a solid foundation for the realization of fiber applications in laser transmission and the biomedical field.

Preparation of biomolecular anthocyanin-immobilized plasma-cured nonwoven fibers from pomegranate (Punica granatum L.) and recycled cotton waste for detection of ammonia

Cotton fibers have been one of the major resources for various modern textile and non-textile industries. They are breathable, soft, and high absorbent natural fibers with a low production cost. Cotton fibers have found uses in a wide range of fields, such as medical field, automobile industry, and furniture design. However, there have been increasing demands to find out other resources for cotton production at high quality and low cost for high technological applications, such as colorimetric sensors. In this work, we provide a novel technique for plasma-induced coloring of nonwoven recycled cotton waste with an anthocyanin natural probe obtained from pomegranate (Punica granatum L.) peel. High-performance liquid chromatography (HPLC) was used to study the anthocyanin extract. Mordant was employed to bind anthocyanin to nonwoven fibers, creating an anthocyanin-mordant coordinative complex. The diameters of the anthocyanin-mordant complex particles were between 5 and 15 nm. A small coating layer of anthocyanin probe was applied to plasma-activated nonwoven cotton. Coloration parameters, absorbance spectra, and colorimetric strength (K/S) data showed that anthocyanin-finished nonwoven cotton had a detection limit of 1–250 ppb of aqueous ammonia, with a corresponding colorimetric change from purple (549 nm) to white (393 nm) due to intramolecular charge transfer. The results demonstrated satisfactory colorfastness of the anthocyanin-dyed nonwoven cotton fibers, UV blocking, and antibacterial efficacy. Promising portable colorimetric technology of anthocyanin-dyed nonwoven cotton fibers was developed for onsite detection of ammonia that can cause severely harmful effects on human organs or even death. Signs of a high surface area in the sensor material include anthocyanin-mordant complex nanoparticles and cotton microfibers.

Self-Healable Multifunctional Fibers via Thermal Drawing.

The development of soft electronics and soft fiber devices has significantly advanced flexible and wearable technology. However, they still face the risk of damage when exposed to sharp objects in real-life applications. Taking inspiration from nature, self-healable materials that can restore their physical properties after external damage offer a solution to this problem. Nevertheless, large-scale production of self-healable fibers is currently constrained. To address this limitation, this study leverages the thermal drawing technique to create elastic and stretchable self-healable thermoplastic polyurethane (STPU) fibers, enabling cost-effective mass production of such functional fibers. Furthermore, despite substantial research into the mechanisms of self-healable materials, quantifying their healing speed and time poses a persistent challenge. Thus, transmission spectra are employed as a monitoring tool to observe the real-time self-healing process, facilitating an in-depth investigation into the healing kinetics and efficiency. The versatility of the fabricated self-healable fiber extends to its ability to be doped with a wide range of functional materials, including dye molecules and magnetic microparticles, which enables modular assembly to develop distributed strain sensors and soft actuators. These achievements highlight the potential applications of self-healable fibers that seamlessly integrate with daily lives and open up new possibilities in various industries.

Soft Polymer Optical Fiber Sensors for Intelligent Recognition of Elastomer Deformations and Wearable Applications.

In recent years, soft robotic sensors have rapidly advanced to endow robots with the ability to interact with the external environment. Here, we propose a polymer optical fiber (POF) sensor with sensitive and stable detection performance for strain, bending, twisting, and pressing. Thus, we can map the real-time output light intensity of POF sensors to the spatial morphology of the elastomer. By leveraging the intrinsic correlations of neighboring sensors and machine learning algorithms, we realize the spatially resolved detection of the pressing and multi-dimensional deformation of elastomers. Specifically, the developed intelligent sensing system can effectively recognize the two-dimensional indentation position with a prediction accuracy as large as ~99.17%. The average prediction accuracy of combined strain and twist is ~98.4% using the random forest algorithm. In addition, we demonstrate an integrated intelligent glove for the recognition of hand gestures with a high recognition accuracy of 99.38%. Our work holds promise for applications in soft robots for interactive tasks in complex environments, providing robots with multidimensional proprioceptive perception. And it also can be applied in smart wearable sensing, human prosthetics, and human-machine interaction interfaces.

Improving the Accuracy of the Evaluation Method for the Interfacial Shear Strength of Fiber-Reinforced Thermoplastic Polymers through the Short Beam Shear Test.

Short fiber-reinforced thermoplastic polymers (SFRTPs) are commonly used in various molding methods due to their high specific elasticity and strength. To evaluate the interfacial strength, several determination methods have been proposed, including the interfacial shear strength (IFSS). In previous research, an IFSS evaluation method based on the short beam shear method was proposed. However, this method is only applicable to micrometer-sized fibers with high stiffness levels that are not easily bent. When utilizing cellulose fiber, the interfacial shear strength (IFSS) results frequently exhibit significant deviations. To tackle this issue, we suggest an enhanced experimental technique that employs beam-shaped specimens with welding points based on the short beam shear test. Furthermore, we conducted a three-dimensional analysis of the original method to determine the fiber orientation angle and IFSS. The outcomes were compared with previously reported determinations. The IFSS achieved through the novel method proposed in this paper exhibits high precision and reliability, rendering it suitable for use with soft and flexible fibers.

Observation of Visible Upconversion Luminescence of Soft Glass Multimode Fibers

This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications.

P T-symmetry breaking in dual-core phosphate-glass photonic crystal fibers.

We investigate the properties of a soft glass dual-core photonic crystal fiber for application in multicore waveguiding with balanced gain and loss. Its base material is a phosphate glass in a P2O5-Al2O3-Yb2O3-BaO-ZnO-MgO-Na2O oxide system. The separated gain and loss cores are realized with two cores with ytterbium and copper doping of the base phosphate glass. The ytterbium-doped core supports a laser (gain) activity under excitation with a pump at 1000 nm wavelength, while the CuO-doped is responsible for strong attenuation at the same wavelength. We establish conditions for an exact balance between gain and loss and investigate pulse propagation by solving a system of coupled generalized nonlinear Schrödinger equations. We predict two states of light under excitation with hyperbolic secant pulses centered at 1000 nm: 1) linear oscillation of the pulse energy between gain and loss core (P T-symmetry state), with strong power attenuation; 2) retention of the pulse in the excited gain core (broken P T-symmetry), with very modest attenuation. The optimal pulse energy levels were identified to be 100 pJ (first state) and 430 pJ (second state).

Plateau-Rayleigh instability of a soft layer coated on a rigid cylinder.

We study the Plateau-Rayleigh instability of a soft viscoelastic solid layer coated on a rigid cylinder i.e., a soft fibre with a rigid core. The onset of instability is examined using a linear stability analysis. We find that increasing the rigid cylinder radius or the stiffness of the layer reduces the growth rate of the fastest growing mode. For each rigid cylinder radius, a critical elastocapillary number is found below which all wavelengths of disturbances are stable. The critical value for a soft fibre with a thick rigid cylindrical core can be several orders of magnitudes larger than that for a totally soft fibre (no rigid core). This highlights the strong stabilizing effect of the rigid core on the system. Increasing the relaxation timescale of the viscoelastic material also slows down the growth of disturbances, but has no effect on the critical elastocapillary number. Interestingly, the wavelength of the fastest growing mode is independent of the rigid cylinder radius for the purely elastic case.

Research Progress of Mid-infrared Supercontinuum Generation Based on Soft Glass Fiber

Research Progress of Mid-infrared Supercontinuum Generation Based on Soft Glass Fiber

A Fiber Sensor for Long-Term Monitoring of Extracellular Potassium Ion Fluctuations in Chronic Neuropsychiatric Diseases.

The extracellular potassium ion concentration in the brain exerts a significant influence on cellular excitability and intercellular communication. Perturbations in the extracellular potassium ion level are closely correlated with various chronic neuropsychiatric disorders including depression. However, a critical gap persists in performing real-time and long-term monitoring of extracellular potassium ions, which is necessary for comprehensive profiling of chronic neuropsychiatric diseases. Here, a fiber potassium ion sensor (FKS) that consists of a soft conductive fiber with a rough surface and a hydrophobic-treated transduction layer interfaced with a potassium ion-selective membrane is found to solve this problem. The FKS demonstrates stable interfaces between its distinct functional layers in an aqueous environment, conferring an exceptional stability of 6 months in vivo, in stark contrast to previous reports with working durations from hours to days. Upon implantation into the mouse brain, the FKS enables effective monitoring of extracellular potassium ion dynamics under diverse physiological states including anesthesia, forced swimming, and tail suspension. Using this FKS, tracking of extracellular potassium ion fluctuations that align with behaviors associated with the progression of depression over months is achieved, demonstrating its usability in studying chronic neuropsychiatric disorders from a new biochemical perspective.

Strain Measurement with Optic Fibers for Structural Health Monitoring of Woven Composites: Comparison with Strain Gauges and Digital Image Correlation Measurements.

In this work, the strains measured with optic fibers and recorded during tensile tests performed on carbon/epoxy composite specimens were compared to those recorded by strain gauges and by Digital Image Correlation (DIC). The work aims at investigating the sensitivity of embedded and glued optic sensors for structural health monitoring applications in comparison with strain gauges and the full field strain map of the DIC. Acrylate, polyimide optic fibers, and three strain gauge sizes are considered to compare the three techniques. Results show hard polyimide-coated sensors are more sensitive to the material pattern than soft acrylate-coated fibers, which also require extensive adhesion length. The work shows a comparable size of strain gauges and material meso-structure is also critical for properly assessing material properties. The Young's modulus computed with the three different techniques is used to define a strategy that supports the selection and the proper size of the adopted strain measuring system for structural health monitoring of composite materials.

Soft glass optical fiber characterization with X-ray computed microtomography

The high loss due to the presence of strong phonon resonances makes silica fibers unfit for applications in the mid-infrared spectral range. This has led to the development of specialty optical fibers, based on novel materials and manufacturing techniques. In some cases, the characterization of these new fibers by means of standard techniques may be challenging. Fiber manufacturers would strongly benefit from a tool, which is capable of checking the geometrical and optical properties of fibers (either after fiber drawing, or even in real-time, during the drawing process). Here, we propose and demonstrate that absorption contrast X-ray computed microtomography is a non-destructive technique, capable of characterizing both geometrical and optical properties of specialty optical fibers. We experimentally verified that the tomographic intensity profile in the fiber core has the same shape as the refractive index profile, which we determined via energy-dispersed X-ray spectroscopy. We tested step- and graded-index soft glass fibers, both purchased and made in-house. Owing to the presence of high atomic number elements, which provide higher X-ray cross-section, soft glasses were more suitable than silica for their characterization via X-ray computed microtomography.

3D soft glass printing of preforms for microstructured optical fibers

We report on the development of a 3D printing process dedicated to the production of soft glass optical fibers. Direct printing with a miniaturized crucible for melting glass blocks with a pneumatic extrusion head was established. For 3D printing, a developed in-house heavy metal oxide glass was used. Contrary to previous studies on 3D printing of optical fiber preforms, the proposed process is based on the deposition of straight horizontally-oriented lines with a diameter of 300–500 µm to replace standard stack-and-draw manual assembly technique typically used in the development of microstructured optical fiber preforms. A test fiber preform composed of 2500 microrods with dimensions of 60x25x25 mm was printed. As a proof of concept, a photonic crystal fiber preform composed of a solid core and 3 rings of air holes in photonic crystal cladding was printed, and further processed into the optical fiber using a standard fiber drawing tower. We measured a single mode performance of fabricated fibers at 1.55 µm, and flat dispersion in the range of 1.6 – 2.2 µm with zero dispersion wavelength at 1.70 µm.

MATLAB-Based Algorithm and Software for Analysis of Wavy Collagen Fibers.

Knowledge of soft tissue fiber structure is necessary for accurate characterization and modeling of their mechanical response. Fiber configuration and structure informs both our understanding of healthy tissue physiology and of pathological processes resulting from diseased states. This study develops an automatic algorithm to simultaneously estimate fiber global orientation, abundance, and waviness in an investigated image. To our best knowledge, this is the first validated algorithm which can reliably separate fiber waviness from its global orientation for considerably wavy fibers. This is much needed feature for biological tissue characterization. The algorithm is based on incremental movement of local regions of interest (ROI) and analyzes two-dimensional images. Pixels belonging to the fiber are identified in the ROI, and ROI movement is determined according to local orientation of fiber within the ROI. The algorithm is validated with artificial images and ten images of porcine trachea containing wavy fibers. In each image, 80-120 fibers were tracked manually to serve as verification. The coefficient of determination R2 between curve lengths and histograms documenting the fiber waviness and global orientation were used as metrics for analysis. Verification-confirmed results were independent of image rotation and degree of fiber waviness, with curve length accuracy demonstrated to be below 1% of fiber curved length. Validation-confirmed median and interquartile range of R2, respectively, were 0.90 and 0.05 for curved length, 0.92 and 0.07 for waviness, and 0.96 and 0.04 for global orientation histograms. Software constructed from the proposed algorithm was able to track one fiber in about 1.1 s using a typical office computer. The proposed algorithm can reliably and accurately estimate fiber waviness, curve length, and global orientation simultaneously, moving beyond the limitations of prior methods.