Flexible ceramic fibers (FCFs) have been developed for various advanced applications due to their superior mechanical flexibility, high temperature resistance, and excellent chemical stability. In this article, we present an overview on the recent progress of FCFs in terms of materials, fabrication methods, and applications. We begin with a brief introduction to FCFs and the materials for preparation of FCFs. After that, various methods for preparation of FCFs are discussed, including centrifugal spinning, electrospinning, solution blow spinning, self-assembly, chemical vapor deposition, atomic layer deposition, and polymer conversion. Recent applications of FCFs in various fields are further illustrated in detail, including thermal insulation, air filtration, water treatment, sound absorption, electromagnetic wave absorption, battery separator, catalytic application, among others. Finally, some perspectives on the future directions and opportunities for the preparation and application of FCFs are highlighted. We envision that this review will provide readers with some meaningful guidance on the preparation of FCFs and inspire them to explore more potential applications.
In recent years, electrospun nanofibers have attracted great attention for their facile adjustable structure, morphology feature and chemical composition. Especially, significant interest has been devoted to the development of electrospun nanofibers with multiscale pores from micropores and mesopores to macropores, owing to their large specific surface area, hierarchical pore structures, abundant active sites and many other unique properties and applications. This review presents an overview on the design strategies, preparation methods, physical properties and applications of electrospun hierarchical porous nanofibers. At first, electrospinning fabrication of nanofibers with different types of pores including micropores, mesopores, macropores and hierarchical pores are introduced. Then the structures, properties of electrospun porous nanofibers and their applications in several important areas, such as catalysis, energy storage, adsorption and separation, heat insulation and flame retardant, sound absorption and wave absorption, sensor and biomedical are summarized. At last, challenges and potential opportunities of electrospun porous nanofibers in the future are highlighted.
In recent years, the carbon-based fibers (CBFs) including carbon fibers, carbon nanotube fibers and graphene fibers have received extensive attention due to excellent thermal, electrical and mechanical properties. Here, the current status of CBFs is reviewed from the following aspects: sprecursors, preparation, performance and application. The precursor systems including acrylonitrile copolymers, pitch, cellulose and lignin, carbon nanotube, graphene and other rare synthetic polymeric precursors. The relationship of preparation method and performance of CBFs is presented. In addition, this review gives the overview of application and future development of CBFs.
Natural fiber-reinforced polymers remained a hot topic of interest in material sciences over the last two decades. Such fibers are appealing in composite materials due to their renewability, low density, better specific strength, biodegradability, accessibility, and low cost. Polymers reinforced with natural fibers provide improved mechanical performance at a lower cost and could be the best alternative to synthetic fibers. Bio-fillers have gained much attention nowadays due to their cost-effectivity and the ability to modify base materials in the composite structure. Natural materials reinforced epoxy composites have a high capacity due to their eco-friendliness, economic feasibility, and technical viability. However, some parameters directly influence desired product performance. This review discusses various properties of natural fibers and their impact on the overall performance of natural fiber-based epoxy composites. It summarizes the recent research on natural fibers/bio-fillers reinforced epoxy biocomposites.
Silk extracted from the cocoon of silkworm has been used as textile materials for thousands of years. Recently, silk has been redefined as a protein-based biomaterial with great potential in biomedical applications owing to its excellent mechanical properties, biocompatibility, and biodegradability. With the advances in silk processing technologies, a broad range of intriguing silk-based functional biomaterials have been made and applied for various biomedical uses. However, most of these materials are based on natural silk proteins without chemical modification, leading to limited control of properties and functions (e.g., biodegradability and bioactivity). A chemical toolbox for modifying the silk proteins is required to achieve versatile silk-based materials with precisely designed properties or functions for different applications. Furthermore, inspired by the traditional fine chemical industry based on synthetic chemistry, developing silk-based fine chemicals with special functions can significantly extend the applications of silk materials, particularly in biomedical fields. This review summarizes the recent progress on chemical modification of silk proteins, focusing on the methodologies and applications. We also discuss the challenges and opportunities of these chemically modified silk proteins.
Fiber materials are promising for electrocatalysis applications due to their structural features including high surface area, controllable chemical compositions, and abundant composite forms. In the past decade, considerable research efforts have been devoted to construct advanced fiber materials possessing conductive network (to facilitate efficient electron transport) and large specific surface area (to support massive catalytically active sites) to boost electrocatalysis performance. Herein, we focused on recent advances in fiber-based electrocatalyst with enhanced electrocatalytic activity. Moreover, the synthesis, structure, and properties of fiber materials and their applications in hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction are discussed. Finally, the research challenges and future prospects of fiber materials in electrocatalysis applications are proposed.
Considering the growing concerns about natural resource depletion, energy inequality, and climate crises, biomass-derived materials—the most abundant organic matter on the planet—have received a lot of attention as a potential alternative to petroleum-based plastics. Herbaceous biomasses and extracted cellulose have recently been extensively used in the development of high-performance and multifunctional materials. Herbaceous biomass has sparked interest due to its species diversity, abundance, low cost, lightweight, and sustainability. This review discusses the structure versus property relationships of various sources of herbaceous biomasses (e.g., sugarcane, straw, and bamboo) and their extracted biomaterials, as well as the latest emerging applications from macro- and microscales to nanoscales. High-strength structural materials, porous carbon materials, multichannel materials, and flexible materials are examples of these applications, which include sustainable electronics, environmentally friendly energy harvesting, smart materials, and biodegradable structural buildings.
Gelatin (G) is a commonly used natural biomaterial owing to its good biocompatibility and easy availability. However, using pure gelatin as a bioink can barely achieve an ideal shape fidelity in 3D printing. In this study, Antheraea pernyi silk fibroin nanofibers (ASFNFs) with arginine-glycine-aspartic acid (RGD) peptide and partial natural silk structure are extracted and combined with pure gelatin bioink to simultaneously improve the shape fidelity and cytocompatibility of corresponding 3D printed scaffold. Results show that the optimum printing temperature is 30 °C for these bioinks. The printed filaments using 16G/4ASFNFs bioink (16wt% gelatin and 4wt% ASFNFs) demonstrate better morphology and larger pore size than those printed by pure gelatin bioink (20G, 20wt% gelatin), thus successfully improve the shape fidelity and porosity of the 3D printed scaffold. The 16G/4ASFNFs scaffold also demonstrate higher swelling ratio and faster degradation rate than the pure gelatin scaffold. Moreover, the cell viability and proliferation ability of Schwann cells cultured on the 16G/4ASFNFs scaffold are significantly superior than those cultured on the pure 20G scaffold. The ASFNFs enhanced 16G/4ASFNFs scaffold reported here are expected to be a candidate with excellent potential for biomedical applications.
Developing efficient and durable non-noble metal-based oxygen evolution catalysts is of great importance for electrochemical water splitting. Here, we report a new and facile strategy for controllable synthesis of high-valence Mo modified FeNiV oxides as efficient OER catalysts. The Mo-dopant displays a significant influence on the valence state of Fe species in the catalysts, which lead to tunable OER performance. When the feed ratio of Mo-dopant is 5%, the Mo-modified FeNiV oxide shows the best OER performance in terms of low overpotential (237 mV at the current density of 10 mA cm−2), Tafel slope (38 mV per decade), and high mass activity, which exceeds its counterparts and most reported OER catalysts. Furthermore, by assembling the catalyst with a carbon fiber cloth, the fabricated water-splitting device exhibits excellent activity and long-term durability in alkaline electrolyte compared with commercial catalysts equipped device. This work not only provides a series of Mo-modified FeNiV-based oxides as high-performance OER catalysts but also offers a new pathway to tune the charge states of OER active centers.
Granular hydroxyl-functionalized UHMWPE was successfully prepared through copolymerization of ethylene and 10-undecen-1-ol protected by tri-iso-butylaluminum using a titanium complex. [ tBuNSiMe2(2,7- tBu2Flu)]TiMe2 was activated in hexane by silica-supported modified-methylaluminoxane. Without any additional pretreatments, the obtained polymer powders were transformed into fibers through a gel-spinning and heat drawing process. When compared to fibers generated from the equivalent unfunctionalized UHMWPE or the commercial HUMWPE, both creep resistance and hydrophilic properties were improved in the hydroxy-functionalized UHMWPE fibers without losing tensile strength.
Developing low-cost, efficient oxygen reduction reaction (ORR) catalysts to replace Pt-based materials is urgently required for the application of Zn-air batteries (ZABs) and microbial fuel cells (MFCs). In this work, meso-microporous carbon fibers with tunable defect density were synthesized by carrageenan fibers. A highly defective carbon fiber (HDCFs) was produced which exhibited an outstanding ORR catalytic activity, reaching to the half-wave potential of 0.841 and 0.44 V in alkaline and neutral electrolytes, respectively. These HDCFs can also act as highly efficient air cathodes for ZABs (delivered potential of 0.69 V and power density of 220 mW cm–2 at 300 mA cm–2) and MFCs (high power density of 69.7 mW cm–2). Simulation by the density functional theory indicated that a high density of defections in a carbon based framework can remarkably modulate the electrical properties. For instance the charge entrapments in the carbon active sites may reduce the energy barrier of ORR.
Unobtrusive metastasis and invasion of malignant tumors are major causes for the death of cancer patients, and unfortunately the lack of specificity and abrupt release of anticancer drugs applied to the primary tumors are causing serious side effects in cancer management. Hence, the development of controlled local drug delivery systems that can effectively treat primary tumors and inhibit tumor metastasis is of critical importance for improved cancer therapeutics. Herein, we developed hyaluronic acid (HA)-modified porous fibrous microspheres as a drug delivery system with the functions of long-acting local chemotherapy, tumor metastasis inhibition and magnetic resonance (MR) imaging. Poly (lactic-co-glycolic acid) (PLGA) short fibers obtained by combined electrospinning and homogenization techniques were successfully modified with gadolinium (Gd3+) chelates and HA, which were subsequently mixed with doxorubicin (DOX) to obtain the multifunctional drug-loaded fibrous microspheres of DOX-PLGA-PEI-DTPA-Gd/HA (DOX − PGH) by electrospray and further crosslinking. The developed DOX − PGH microspheres with an average diameter of 118.8 μm possess good structural stability and a high r1 relaxivity, and can achieve long-term DOX release. The cellular and animal experiments demonstrated that the DOX − PGH microspheres could facilitate targeted delivery of DOX to accelerate 4T1 cell death while reducing cancer cell metastasis due to the cooperative actions of long-term DOX-mediated chemotherapy and the fibrous microsphere-induced tumor anchoring to likely avoid primary tumor cell shedding, and render MR imaging of tumors during the treatment. The developed DOX − PGH microspheres may represent one of the updated local tumor chemotherapy formulations for improved tumor therapy with justified antitumor and anti-metastasis efficacy.
Two-dimensional MXene has recently captured widespread research attention in energy storage and conversion fields due to its high conductivity, large specific surface area, and remarkable electro-activity. However, its performance is still hindered by severe self-restacking of MXene flakes. Herein, conductive Ti3C2Tx/carbon nanofiber (CNF) composite aerogel with typical “layer-strut” bracing 3D microscopic architecture has been fabricated via synergistic assembly and freeze-drying process. In virtu of the strong interfacial interaction between polymeric precursor nanofibers and MXene mono-layers, gelation capability and 3D formability of Ti3C2Tx is greatly reinforced, as resulted Ti3C2Tx/CNF aerogels possess a highly ordered microporous structure with interlayered CNF penetrating between large size MXene lamellae. This special configuration guarantees the stability and pliability of the composite aerogels. Furthermore, the 3D form interconnected conductive network and the parallell alignment of the pores allow free electrical carriers motion and ion migration. As a result, the prepared Ti3C2Tx/CNF aerogel-based electrode exhibits an exceptional gravimetric specific capacitance of 268 F g−1 at a current density of 0.5 A g−1 and an excellent cycling stability of 8000 cylcles, and the assembled symmetric supercapacitor, delivers a high energy density of 3.425 W h kg−1 at 6000 W kg−1. This work offers a new route for the rational construction of 3D MXene assembly for advanced energy storage materials.
A good wound dressing needs to promote wound healing and tissue repair when the skin is injured. In this study, a self-made spherical section free surface electrospinning device was used to produce large quantities of electrospun porous polylactic acid (PLA)/chitosan (CS)/aloin nanofiber membranes (NFMs) for antibacterial wound dressing. The porous structures of PLA-based nanofibers were controlled by adjusting the weight ratios of mixed solvent and solute. The results showed that high-quality porous PLA/CS/aloin (PCA) NFMs were obtained when the weight ratios of chloroform/N, N-dimethylformamide and PLA: CS were 90/10 and 7:1, respectively. The porous PCA NFMs exhibited high porosity, acceptable mechanical properties, moderate hydrophobicity, good swelling property, and high water vapor transmission rate. Moreover, they also showed excellent blood coagulative, antibacterial, biocompatible properties, which had the potential to be used in the application of antibacterial wound dressings.
Fluorescent polymer dots (Pdots) have the advantages of excellent optical properties, great biocompatibility and high photostability. Herein, we feed ultra-low doses Pdots to silkworms for the first time and aim to prepare dual-performance modified silks. After Pdots feeding, the fluorescence signal of cocoons and degummed silks increases significantly, which is more stable and more uniform than that of post-treatment silks. Moreover, Pdots hinder the conformation transformation of silk fibroin and improve the mechanical property of twisted silk strand. The highest elongation at break point is 20.75 ± 0.03% and breaking strength is 271.7 ± 3.8 MPa. With excellent fluorescence and mechanical properties, the optimized silks are successfully applied as a scaffold for cell culture and imaging. Furthermore, we investigate the metabolism of Pdots in the silkworms for understanding the behaviours of Pdots in the process of silks synthesis and secretion.
Microscale electroporation devices are mostly restricted to in vitro experiments (i.e., microchannel and microcapillary). Novel fiber-based microprobes enable in vivo microscale electroporation and arbitrarily select the cell groups of interest to electroporate. We developed a flexible, fiber-based microscale electroporation device through a thermal drawing process and femtosecond laser micromachining techniques. The fiber consists of four copper electrodes (80 μm), one microfluidic channel (30 μm), and has an overall diameter of 400 μm. The dimensions of the exposed electrodes and channel were customizable through a delicate femtosecond laser setup. The feasibility of the fiber probe was validated through numerical simulations and in vitro experiments. Successful reversible and irreversible microscale electroporation was observed in a 3D collagen scaffold (seeded with U251 human glioma cells) using fluorescent staining. The ablation regions were estimated by performing the covariance error ellipse method and compared with the numerical simulations. The computational and experimental results of the working fiber-based microprobe suggest the feasibility of in vivo microscale electroporation in space-sensitive areas, such as the deep brain.
Wearable sensing technology enables the interaction between the physical world and the digital world, as takes an irreplaceable role in development of the Internet of Things (IoT), and artificial intelligence (AI). However, increasing requirements posed by rapid development of wearable electronic information technology bring about many for wearable sensing technology, such as the demands for ultrahigh flexibility, air permeability, excellent biocompatibility, and multifunctional integration. Herein, we propose a wearable all-fiber multifunctional sensor (AFMS) based on a biocompatible material, i.e., silk fibroin. A simple two-layer configuration of a silk fiber film and an interdigital Ag nanowires (AgNWs) electrode was designed to construct the AFMS, in which silk fibroin simultaneously serves as a fundamental supporting component and a functional sensing component. Electrospinning and spray coating technologies were introduced to process the silk fiber film and the AgNWs electrode. The all-fiber configuration allows AFMS to possess ultrahigh flexibility and good air permeability, and silk fibroin enables the AFMS to have excellent biocompatibility. More importantly, benefiting from the all-fiber structure and the environmentally sensitive dielectric property of silk fibroin, the AFMS presented multiple sensing characteristics, including pressure sensing, temperature sensing, and humidity sensing. Among them, the pressure sensing function reached a high sensitivity of 2.27 pF/kPa (7.5%/kPa) and a remarkable resolution of ~ 26 Pa in the low pressure range. Additionally, the outstanding mechanical reliability and sensing stability of AFMS were proven by a systematic experiment. In addition, the AFMS was successfully applied for smart mask for breathing monitoring and a smart glove for bending angle recognition of finger joints. Multiple sensing characteristics combined with prominent fundamental features enable the AFMS tremendous potential in the smart sensing field, e.g., smart clothing.
Development of biomaterial based flexible electronics has got intensive attention owing to the potential applications in the wearable and epidermal devices. Silk fibroin, as a natural textile material with excellent performance, has been widely concerned by industry and academy. However, the property of electrical insulation limits his development in the field of flexible electronics. In this paper, a regenerated silk fibroin/carbon nanotube (RSF/CNT) conductive film has been successfully fabricated and applied in flexible capacitive-type pressure sensor and wearable triboelectric nanogenerator by a facile method. The electrical conductivity and mechanical property of RSF/CNT film was optimized by investigating with different composite ratio from 10 to 90% (WRSF/WCNT). The RSF/CNT film has a good photothermal response and electric heating performance. We furtherly demonstrated that the RSF/CNT based sensor can be used as epidermal self-powered sensor for multifunction human motion monitoring and Morse code compilation. The observed research results have shown that the RSF/CNT film has a wide range of potential application prospects in the wearable electronics field.
Bone defects are always accompanied by inflammation due to excessive reactive oxygen species (ROS) in injured regions, which greatly impedes the regeneration of bone tissues. Although many conductive polymers have been developed to scavenge ROS, they are typically non-degradable under physiological conditions, making them unsuitable for in vivo applications. Biodegradable polyorganophosphazenes (POPPs) may serve as potent ROS-scavenging biomaterials owing to their versatile chemical structures and ease of functionalization. Herein, a PATGP-type electroactive polyphosphazene with side groups of aniline tetramer and glycine ethyl ester was compared to conventional poly(lactic-co-glycolic acid) (PLGA) in regenerating bone tissues. To conduct in vitro and in vivo evaluations, three kinds of electrospun nanofibrous meshes were prepared: PLGA, PLGA/PATGP blend, and PLGA/PATGP core–shell nanofibers. Among them, PLGA/PATGP core–shell nanofibers outperform the blend and PLGA nanofibers in terms of scavenging ROS, promoting osteogenic differentiation, and accelerating neo-bone formation. The continuous PATGP shell on the PLGA/PATGP core–shell nanofiber surface could apparently provide more significant modulation effects on cellular behaviors than the PLGA/PATGP blend nanofibers with PATGP dispersed in the PLGA matrix. Therefore, the core–shell structured PLGA/PATGP nanofibers were envisioned as a promising candidate scaffold for bone tissue engineering. Additionally, the core–shell design paved the way for biomedical applications of functional POPPs in combination with other polymeric biomaterials, without phase separation or difficulty of increasing the molecular weights of POPPs.
Scaffolds functionalized with graded changes in both fiber alignment and mineral content are more appealing for tendon-bone healing. This study reports the healing of rotator cuff injury using a heterogeneous nanofiber scaffold, which is associated with a structural gradating from aligned to random and an increasing gradient of mineral content in the same orientation. The photothermal-triggered structural change of a nanofiber scaffold followed by graded mineralization is key to constructing such scaffolds. This type of scaffold was found to be biocompatible and provide beneficial contact guidance in the manipulation of tendon-derived stem cell morphologies in vitro. Specifically, tenogenic and osteogenic differentiation of tendon-derived stem cells were simultaneously achieved using the fabricated scaffold. In vivo investigation also showed the improved healing of rabbit rotator cuff injuries based on immunohistochemical analysis and biomechanical investigation that indicates the promising potential of a dual-gradient nanofiber scaffold in clinical tendon-bone healing.
Dual-gradient nanofiber scaffold with transitions in both surface structure and mineral content was designed and manufactured to replicate the native interface between tendon and bone to facilitate the tendon-bone healing in a rabbit rotator cuff injury model.