Ultrafine Fibers Research Articles

Industrial Scale Sea-Island Melt-Spun Continuous Ultrafine Fibers for Highly Comfortable Insulated Aerogel Felt Clothing.

Aerogels are most attractive for thermal clothing. However, mechanical fragility and structural instability restrict their practical applications. These issues are overcome by developing industrial scale sea-island melt-spun ultrafine fibers with large and uniform length-to-diameter as building blocks, which are assembled into aerogel felts with corrugated lamellar structure through freeze-shaping technology. These aerogels possess excellent mechanical properties to meet fabric elasticity and comfort needs, including super-flexibility (25% tensile strain, 95% compression, 180° bending performance) and fatigue resistance of over 10,000 cycles. The aerogels are also self-cleaning, waterproof, breathable, and flame-retardant, making them suitable for application requirements in extreme environments. Moreover, the obtained aerogel felt clothing exhibits excellent thermal insulation properties close to that of dry air, and is only one-third as thick as down clothing with similar insulating properties. Expanding sea-island melt-spun fiber to construct aerogel in this strategy provides scalable potential for developing multifunctional insulating aerogel clothing.

Clinical-relevant sized tubular capillary mimicries by sacrificial core-sheath electrospinning

Electrospinning is a versatile technique that is often used to fabricate ultra-fine fibers. With the help of a coaxial spinneret, microtubes can be fabricated as potential biomimetic capillary vessels. However, the sizes of electrospun microtubes in recent research were around 5 μm which is smaller to native capillary vessels (5–10 μm). The electrospun microtube diameter can be determined by various electrospinning parameters such as spinning materials, solvent, spinning distance, solution pump rate, applied voltage, etc. In this research, we explored the effects of spinning distance and core/sheath pump rate ratio on microtube diameter and wall thickness. Viscosity, wettability, and tensile tests were also conducted for microtube characterization. The results indicated that the microtube diameters range from 5 μm to 12 μm, which provides a promising direction for the fabrication of biomimetic capillary vessels.

Flexural toughness and stress-strain relationship of different types of steel fiber reinforced shotcrete in high geothermal environment

The shape of steel fiber plays a pivotal role in determining the mechanical properties of concrete. In this paper, the impacts of end-hooked, wavy and ultra-fine steel fibers (all with a doping amount of 1.0 %) on the compressive strength, flexural strength, flexural toughness, and strain-strain relationship of shotcrete under curing conditions of 20 ℃, 40 ℃, and 60 ℃ are studied. Furthermore, the flexural toughness of steel fiber shotcrete is evaluated using the energy absorption method, and a constitutive model for steel fiber shotcrete was established based on meso-damage mechanics theory. The results indicate that curing temperatures below 40 ℃ are conducive to enhancing the compressive strength, flexural strength, and flexural toughness of steel fiber shotcrete, while curing temperatures above 60 ℃ are unfavorable for the development of strength and toughness in steel fiber shotcrete. Regardless of the type of steel fiber, its incorporation can alleviate the negative impact of high-temperature curing on the strength and toughness of shotcrete. Under high-temperature curing conditions, the influence of end-hooked steel fibers on the strength of shotcrete is superior to that of corrugated and ultrafine steel fibers, while ultrafine steel fibers are beneficial for improving the flexural toughness of shotcrete. The slope, peak stress, and peak strain of the stress-strain curves of shotcrete cured at 40 ℃ and 60 ℃ with the addition of the three types of steel fibers are greater than those of concrete without steel fibers. Furthermore, the descending segment of the curve is wider and smoother, with a larger surrounding area, demonstrating good toughness, deformability, and ductility. The end-hooked steel fibers and ultrafine steel fibers exhibit superior performance in enhancing the toughness and ductility of shotcrete under high-temperature curing conditions compared to wavy steel fibers. Based on meso-damage theory, the impacts of curing temperature and steel fiber types on the constitutive model of shotcrete under axial compression were established, and the model parameters were discussed. The research results can provide theoretical support for the durability design of tunnel linings in high ground temperature environments.

Green and safe preparation of antibacterial sutures composed of PLA ultrafine fibers

AbstractThe electrospun yarn for sutures has gained worldwide attention due to its fine fibers that resemble the extracellular matrix and its abundant functional sites. However, the use of a large number of toxic solvents poses safety risks and environmental pollution during production, making it challenging to directly apply electrospun yarn in the biomedical field. In this study, an environmentally friendly and safe method without toxic solvents was proposed for preparing antibacterial PLA ultrafine fiber sutures. This method involves melt electrospinning, hot‐stretching, low‐temperature plasma treatment, and chitosan grafting. The PLA ultrafine fiber sutures exhibit a high tensile strength which is 2.04 N before knotting and 1.57 N after knotting. The suture diameter is 118.7 μm and average fiber diameter is 1.72 μm. Chitosan grafted on the fiber surface provides excellent antibacterial properties for the sutures, with antibacterial rates against Escherichia coli and Staphylococcus aureus reaching 99.89% and 99.11%, respectively. The cell survival rate is 97.33%, while hemolysis rate is only 2.35%, demonstrating excellent biocompatibility of PLA ultrafine fiber sutures. This study presents a green and safe method for preparing clinically applicable absorbable antibacterial surgical sutures with high mechanical properties.Highlights A green and safe method for preparing PLA‐CS ultrafine fiber sutures. PLA‐CS suture with a tensile strength of 2.04 N and a fiber diameter of 1.72 μm. PLA‐CS suture with good antibacterial property and biocompatibility.

Characterization of Bacterial Nanocellulose Produced by Tropical Fruit‐Derived Bacteria in Coconut Water Medium Supplemented with Pineapple Peel Extract

AbstractAgro‐industrial residues, such as surplus fruits and vegetables are increasingly recognized as valuable sources for isolating bacterial strains capable of efficiently producing bacterial nanocellulose (BNC). This study presents a novel approach to BNC production using Komagataeibacter intermedius SB 110 isolated from rotten pineapple, cultivated in a sustainable medium of coconut water enriched with 5% sucrose and 0.5% pineapple peel extract. By leveraging agricultural waste, this method accelerates BNC biosynthesis to less than 7 days and achieves a yield of 5.563 g/L over 14 days, a 1.58‐fold increase compared with traditional media. The BNCs were primarily composed of cellulose type I, with minor cellulose type II, ultrafine fiber sizes (58.3 to 84.98 nm) and a high crystallinity index (60.81% to 78.34%), indicating superior structural quality. This innovative process not only demonstrates the potential of using low‐cost, sustainable substrates for high‐yield BNC production but also significantly enhances both the efficiency and scalability of the production process, setting a new standard over existing methods.

Anthocyanin-rich grape pomace extract encapsulated in protein fibers: Colorimetric profile, in vitro release, thermal resistance, and biological activities

Red wine grape pomace is an important source of bioactive compounds with biological activities of interest. Grape pomace extract can be encapsulated in ultrafine fibers using the electrospinning technique. Encapsulation is used to increase stability and protect the phenolic compounds in the extract. In this study, zein fibers were developed for encapsulation of grape pomace extract (0 %, 5 %, 10 %, and 15 % w/w). The extract was evaluated for colorimetric profile, whereas the ultrafine zein fibers carrying the extract were assessed for morphology, loading capacity, in vitro release profile, thermal and thermogravimetric properties, thermal resistance, hydrophilicity, and antioxidant and antimicrobial activities. The grape pomace extract changed color depending on pH, ranging from pink (pH 1) to yellow (pH 13 and 14). The fibers presented a smooth and uniform structure, with diameters of approximately 450 nm and a loading capacity of up to 82 %. The membranes of ultrafine fibers demonstrated hydrophilic behavior, and the in vitro release profile was dependent on the concentration of the added extract. Furthermore, the fibers were observed thermally protect the encapsulated compounds and maintain their antioxidant and antimicrobial activities. These findings indicate that the produced material has potential applications in the development of active and intelligent packaging for the food industry.

Highly aligned electroactive ultrafine fibers promote the differentiation of mesenchymal stem cells into Schwann-like cells for nerve regeneration

This study investigates the efficacy of a novel tissue-engineered scaffold for nerve repair and functional reconstruction following injury. Utilizing stable jet electrospinning, we fabricated aligned ultrafine fibers from dopamine and poly(L-lactic acid) (PLLA), further developing a biomimetic, oriented, and electroactive scaffold comprising poly(pyrrole) (PPy), polydopamine (PDA), and PLLA through dual in situ polymerizations. The scaffold demonstrated enhanced cell adhesion and reactive oxygen species (ROS) scavenging capabilities and promoted the differentiation of mesenchymal stem cells (MSCs) into Schwann-like cells, essential for nerve regeneration. In vivo assessments revealed significant peripheral nerve regeneration in 10 mm sciatic nerve defects in rats, with observations made 12 weeks post-transplantation. This included facilitated myelination and increased muscle density on the injured side, leading to improved motor function recovery. Our results suggest that the aligned PPy/PDA/PLLA fibrous scaffold offers a promising approach for promoting the differentiation of MSCs into Schwann-like cells conducive to nerve regeneration and represents a significant advancement in nerve repair technologies. This study provides a foundational basis for future research into tissue-engineered solutions for nerve damage, potentially impacting clinical strategies for nerve reconstruction.

Electrospun Fiber‐Based Tubular Structures as 3D Scaffolds to Generate In Vitro Models for Small Intestine

AbstractRecently, in vitro models emerge as valuable tools in biomedical research by enabling the investigation of complex physiological processes in a controlled environment, replicating some traits of interest of the biological tissues. This study focuses on the development of tubular polymeric scaffolds, made of electrospun fibers, aimed to generate three‐dimensional (3D) in vitro intestinal models resembling the lumen of the gut. Polycaprolactone (PCL) and polyacrylonitrile (PAN) are used to produce tightly arranged ultrafine fiber meshes via electrospinning in the form of continuous tubular structures, mimicking the basement membrane on which the epithelial barrier is formed. Morphological, physical, mechanical, and piezoelectric properties of the PCL and PAN tubular scaffolds are investigated. They are cultured with Caco‐2 cells using different biological coatings (i.e., collagen, gelatin, and fibrin) and their capability of promoting a compact epithelial layer is assessed. PCL and PAN scaffolds show 42% and 50% porosity, respectively, with pore diameters and size suitable to impede cell penetration, thus promoting an intestinal epithelial barrier formation. Even if both polymeric structures allow Caco‐2 cell adhesion, PAN fiber meshes best suit many requirements needed by this model, including highest mechanical strength upon expansion, porosity and piezoelectric properties, along with the lowest pore size.

Effect of γ-radiation on silica aerogel and composite material for thermal insulation applications in nuclear power pipeline

SiO2 aerogel and its composite materials are considered as promising high-temperature thermal insulation materials due to their high porosity, low density and low thermal conductivity. However, a major obstacle for their application in nuclear power systems is the currently insufficient mechanism of the radiation effect. This study therefore aimed to investigated the changes in the microstructure, hydrophobic properties and thermal insulation properties of aerogel and ultrafine glass fiber reinforced aerogel composite (uGF/SiO2 aerogel) before and after γ-radiation, and explore the mechanism of the γ-radiation effect of aerogel materials. With an increase in cumulative radiation dose, the microstructure of aerogel suffered significant radiation damage, causing a gradual increase in crystallinity and thermal conductivity. When the cumulative dose reached 1700 kGy, the nanoparticles in the aerogel agglomerated and crystallized significantly, leading to an approximately 30 % increase in thermal conductivity. Notably, at the radiation of 1700 kGy, the uGF/SiO2 aerogel exhibited excellent structure stability, with a thermal conductivity of 31.60 mW/m·K, which was 3.27 % higher than that of unirradiated sample. This indicated the uGF/SiO2 aerogel exhibited excellent thermal performance and thermal stability even after γ-radiation. The study on the radiation effect of aerogel materials offers valuable insights for the composition optimization of aerogel used in nuclear power applications.

Enhanced ultrafine multimode fiber imaging based on mode modulation through singular value decomposition

Enhanced ultrafine multimode fiber imaging based on mode modulation through singular value decomposition

Towards superior thermal insulation: Flexible Kevlar aerogel fibers with ultrafine size

Aramid aerogel fibers, characterized by their 3D porous structure, high specific area, etc., are emerging as thermal insulation materials with significant appeal for high-temperature applications. To obtain better thermal shielding and more compact aerogel fabrics, ultrafine, highly flexible and easily bendable aerogel fibers have been developed, called ultrafine Kevlar aerogel fibers (UKAF). These fibers are observed to be about 100 μm in diameter, finer than reported in most previous studies, and perform well in tensile and heat resistance. The breaking strength of the UKAFs can be as high as 6.5 MPa, thanks to the use of high-concentration spinning suspensions. Besides, these ultrafine fibers also inherit the excellent thermal stability of Kevlar, almost do not decompose before 480 °C. In addition, the resultant UKAFs can be easily twisted, knotted, and braided. The fabrics braided from such fibers are able to show a significant temperature drop gradient of 130 °C mm−1 when exposed to a hot plate of 300 °C, indicating superb performance in thermal insulation. Given these, the flexible UKAFs prepared in this study that possess a distinctive set of properties will be highly advantageous across various applications, particularly in the field of thermal insulation.

Investigation of electrospinning parameters and fiber collection methods on morphology of thermoplastic polyester elastomer fibers

Electrospinning is an easy and simple process for the preparation of ultrafine fibers with tunable morphology. Thermoplastic Elastomers (TPEs) are engineering polymers with an elastomeric nature that can be processed as thermoplastics. They can be classified based on their chemical structure and polyester-based TPEs are counted as high-performance materials due to their mechanical properties and can be used for various applications from automotive, construction, furniture, and consumer goods. In this study, electrospun polyester-based thermoplastic elastomer fibers were prepared and characterized. Thermoplastic polyester elastomer, Hytrel 4056 was used as the polymer, and chloroform was used as a solvent. The effects of polymer: solvent weight ratio, feed rate, applied voltage, and collector type were investigated in terms of fiber formation and morphology. For this aim, the polymer: solvent weight ratio was varied as 1:7, 1:11, and 1:15; the feed rate was set to 1 and 3 ml h-1. To collect the fibers metal plate and water bath collectors were used at a constant needle-to-collector distance under 10, 15, and 20 kV. The viscosity of the polymer solutions was measured as a function of the polymer: solvent ratio to observe the effects of viscosity on fiber morphology.

Superhydrophobic stereocomplex-type polylactide/ultra-fine glass fibers aerogel for passive daytime radiative cooling

Passive daytime radiative cooling (PDRC) technology offers a green and sustainable strategy for cooling, eliminating the need for external energy sources through its exceptional efficiency in heat radiation and sunlight reflection. Despite its benefits, the widespread usage of non-biodegradable PDRC materials has unfortunately caused environmental pollution and resource wastage. Furthermore, the effectiveness of outdoor PDRC materials can be significantly diminished by rainfall. In this work, a superhydrophobic composite aerogel composed of stereocomplex-type polylactide and ultra-fine glass fiber has been successfully developed through simple physical blending and freeze-drying, which exhibits low thermal conductivity (36.26 mW m−1 K−1) and superhydrophobicity (water contact angle up to 150°). Additionally, its high solar reflectance (91.68 %) and strong infrared emissivity (93.95 %) enable it to effectively lower surface temperatures during daytime, resulting in a cooling effect of approximately 3.8 °C below the ambient temperature during the midday heat of summer, with a cooling power of 68 W/m2. This aerogel offers an environmentally friendly and sustainable approach for the utilization of radiative refrigeration materials, paving the way for environmental protection and sustainable development.

Gelatin/EGDE Ultrafine Composite Fibers Reinforced with 3D Spacer Fabric as Bicomponent Scaffolds for Tissue Engineering.

Protein-based ultrafine fibrous scaffolds can mimic the native extracellular matrices (ECMs) with regard to the morphology and chemical composition but suffer from poor mechanical and wet stability. As a result, cells cannot get a true three-dimensional (3D) environment as they find in native ECMs. In this study, an epoxide, ethylene glycol diglycidylether (EGDE), with high reactivity to active hydrogen is introduced to gelatin solution, serving as an effective cross-linker. The gelatin/EGDE 3D-ultrafine (∼500 nm in diameter) fibrous composite scaffolds are made by an ultralow-concentration phase separation technique (ULCPS). The effects of the polymer content and modification conditions on the morphology and wet stability of the constructs are investigated. It is revealed that ultrafine fibers with 3D random orientation could be formed at low concentrations (0.01, 0.05, and 0.1 wt %, respectively). The wet stability of the constructs could be effectively improved by introducing EGDE into the gelatin system. The shrinkage is reduced to merely 2.14% after the modification at 120 °C for 2 h and could be maintained for up to 3 days. In order to improve the compression properties, the same technique is utilized with the presence of a poly(lactic acid) (PLA) spacer fabric to produce a bicomponent scaffold. The mechanical property and cell viability of the bicomponent scaffolds are investigated, and it is found that cells could enter deep inside and orient themselves randomly at the central area of the bicomponent scaffold. The modification and design approach presented in this study has the potential to provide various protein-based ultrafine fibrous biomaterials for a variety of biomedical applications.

Self-supported lignin-based carbon fibrous aerogels with outstanding rate capability and high oil/seawater separation flux

The construction of hardwood kraft lignin (HKL)-based carbon fibrous aerogels (LCAs) for practical application still faces significant challenges. In this work, we proposed to enhance LCAs through the utilization of hydrogen-bonding interactions and π-π interactions. Self-supported LCA/graphene oxide (GO) composites were prepared based on the adhesion of HKL ultrafine fibers and GO, taking advantage of the strong interaction between HKL and GO. The morphology, thermal behavior, chemical structure and crystalline structure of LCA/GO composites were systemically investigated and discussed. Results suggested that HKL ultrafine fibers and GO formed a cohesive whole carbonization due to the influence of hydrogen-bonding and π-π interaction. The prepared LCA/GO composites exhibited outstanding rate capability and high oil/seawater separation flux with their three-dimensional hierarchical channel structures. The specific capacitance of the LCA/GO5.0 electrode was 152 F g−1 at 0.5 A g−1 and 94 F g−1 at 10 A g−1, respectively, while maintaining a retention rate of 113 % after 2000 cycles. The adsorption capacity of the LCA/GO7.5 composite reached up to 55.9 g g−1 and its oil/seawater separation flux was as high as 12,335 L m−2 h−1. The formation strategy, sustainable concept and excellent properties presented in this work will give some inspiration for the preparation of self-supported aerogels as well as their applications in compressible supercapacitors and oil/seawater separation.

High‐strength, recyclable and healable polyurea/aramid fiber elastomeric composites

AbstractThe demanding and rigorous modern work environments present significant challenges to the protective capabilities of engineering materials. Polyurea elastomers often face limitations in terms of inadequate strength and a lack of weather resistance, however, polyurea composites holds great promise in addressing these issues. This study prepared modified ultrafine aramid short fibers using a mechanochemical method. Subsequently, in‐situ polymerization was utilized to combine the modified ultrafine aramid short fibers (M‐AF) with polyurea, resulting in the synthesis of a composite material characterized by recyclability, robust weather resistance, and favorable mechanical properties. Subsequently, intensive researches were conducted on the mechanical properties, recyclability, self‐healing performance, weather resistance, and chemical medium resistance of the composites. The composite at 0.1 wt% of M‐AF exhibited improvements in tensile strength (27.2 ± 0.8 MPa) as well as obviously enhanced impact performance (428.8 ± 6 kJ/m2), and recovered most of its mechanical properties after recycling and self‐healing. Moreover, the composite exhibits excellent weather resistance and chemical resistance, enabling it to uphold its exceptional protective performance even in the face of challenging environments.Highlights Ultrafine aramid fibers were prepared using a simple mechanochemical method. Mechanochemical methods were employed to surface modify aramid fibers. The composites have good strength, recyclability, weather resistance.

PTFE foam coating ultrafine glass fiber composite filtration material with Ultra-Clean emissions

Bag filters are widely used for dust removal in the industrial applications with filtration materials serving as the critical component. It is meaningful to develop filtration materials with ultra-clean emission effect, as the emitted gas can be proceeded directly by carbon capture technologies. In this study, we introduced a novel approach to fabricate a kind of gradient-structured filtration material by wet-laying ultrafine glass fibers on the surface of aramid fiber needle-punched nonwoven fabrics, followed by PTFE emulsion foam coating. Our PTFE foam coating ultrafine glass fiber composite filtration material demonstrated remarkable filtration performance, achieving a high filtration efficiency up to 99.86 % and a low pressure drop of 87.54 Pa. After undergoing 30 cycles of filtration, the particulate emission concentration was 0.4327 mg m−3. Significantly, this innovative filtration material exhibited exceptional stability, primarily attributable to the surface filtration effect of the PTFE foam coating layer. This innovative design provided a kind of new direction for the flue gas filtration and the emitted clean air can be capture by carbon capture technologies directly.

Synthesis of silsesquioxane-linked polyester with liquid crystalline backbone chain

A novel procedure for the synthesis of a 3D network polyester bearing silsesquioxane cores was executed to prepare the ternary silsesquioxane-linked copolyester BNH (BNH4 and BNH8) based on 4-acetoxy benzoic acid (ABA), 6-acetoxy-2-naphthoxylic acid (ANA), and a silsesquioxane-cored monomer (CSQ-AHA4 or CSQ-AHA8). The thermal data and phase behavior indicated that moderate crosslinking would reduce the stacking of the backbones, thereby enhancing the mobility of the backbone. However, greater crosslinking would limit the movement of the backbone, while the 3D cross-linked structure enhanced the structural stability of the phase region and the uniformity of the crystal size distribution. The loose fiber bundles showed that the participation of the 3D configuration and silsesquioxane increased the chain flexibility, and facilitated the formation of strong polyester ultrafine fibers. It was possible to improve the lateral mechanical properties of the oriented polyester materials, probably improving the mechanical properties aspect ratio of thin film materials.

Biomimetic grafts from ultrafine fibers for collagenous tissues.

The ligament is the soft tissue that connects bone to bone and, in case of severe injury or rupture, it cannot heal itself mainly because of its poor vascularity and dynamic nature. Tissue engineering carries the potential to restore the injured tissue functions by utilization of scaffolds mimicking the structure of native ligament. Collagen fibrils in the anterior cruciate ligament (ACL) have a diameter ranging from 20 to 300nm, which defines the physical and mechanical properties of the tissue. Also, the ACL tissue exhibited a bimodal distribution of collagen fibrils. Currently, the ability to fabricate scaffolds replicating this structure is a significant challenge. This work aims at i) measuring the diameter of collagens of bovine ACL tissue, ii) investigating the fabrication of sub-100nm fibers, and iii) fabricating aligned scaffolds with bimodal diameter distribution (with two peaks) resembling the healthy ACL structure. It is hypothesized that such scaffolds can be produced by electrospinning polycaprolactone (PCL) solutions. To test the hypothesis, various PCL solutions were formulated in acetone and formic acid in combination with pyridine, and electrospun to generate sub-100nm fibers. Next, this formulation was adjusted to produce nanofibers with a diameter between 100nm and 200nm. Finally, these solutions were combined in the co-electrospinning process, i.e., two-spinneret electrospinning, to fabricate biomimetic scaffolds with a bimodal distribution. Electrospinning of 8% and 15% PCL solutions, respectively, resulted in the production of fibers with diameters below and above 100nm. The combined scaffold exhibited a bimodal distribution of aligned fibers with peaks around 80 and 180nm, thus mimicking the collagen fibrils of healthy ACL tissue. This research is expected to have a society-wide impact because it aims to enhance the health condition and life quality of a wide range of patients.

Precise Fabrication and Manipulation of Individual Polymer Nanofibers.

Polymer nanofibers hold promise in a wide range of applications owing to their diverse properties, flexibility, and cost effectiveness. In this study, we introduce a polymer nanofiber drawing process in a scanning electron microscope and focused ion beam (SEM/FIB) instrument with in situ observation. We employed a nanometer-sharp tungsten needle and prepolymer microcapsules to enable nanofiber drawing in a vacuum environment. This method produces individual polymer nanofibers with diameters as small as ∼500 nm and lengths extending to millimeters, yielding nanofibers with an aspect ratio of 2000:1. The attachment to the tungsten manipulator ensures accurate transfer of the polymer nanofiber to diverse substrate types as well as fabrication of assembled structures. Our findings provide valuable insights into ultrafine polymer fiber drawing, paving the way for high-precision manipulation and assembly of polymer nanofibers.