Fabrication of one-dimensional colloidal assemblies from electrospun nanofibers

SiO2-based inorganic nanofiber aerogel with rapid hemostasis and liver wound healing functions

Non-compressible hemostasis and promoting tissue healing are important in soft tissue trauma repair. Inorganic aerogels show superior performance in rapid hemostasis or promoting tissue healing, but simultaneously promoting non-compressive hemostasis and soft tissue healing still remains a challenge. Herein, SiO2-based inorganic nanofiber aerogels (M2+@SiO2, M=Ca, Mg, and Sr) were prepared by freeze-drying the mixture of bioactive silicates-deposited SiO2 nanofibers and SiO2 sol. These M2+@SiO2 aerogels have a three-dimensional highly-interconnected porous structure, remarkable flexibility, high absorption, good hydrophilicity, negative zeta potential, and bioactive ions releasing capacity. M2+@SiO2 aerogels not only exhibited satisfactory hemostasis activities in vitro, but also possessed high hemostatic efficacy in compressible rabbit femoral artery injury bleeding model and non-compressible rat liver puncture bleeding model compared to medical gauze and gelatin sponge. M2+@SiO2 aerogel had low blood clotting index of Ca. 10 % and short partial thromboplastin time of ca. 82 s in vitro, and could greatly short bleeding time by >50 % and decrease blood loss by about 80 % compared to medical gauze and gelatin sponge in non-compressible hemostasis. Sr2+@SiO2 aerogel showed optimal bioactivities on promoting cell proliferation, cell migration, and the expression of liver function and angiogenesis related genes and proteins in vitro. Importantly, Sr2+@SiO2 aerogel possessed a noteworthy function to promote liver soft tissue healing in vivo by releasing bioactive ions and providing a highly-interconnected porous structure to support vascular development and tissue regeneration. Overall, Sr2+@SiO2 aerogel has great potential for integrated rapid hemostasis and soft tissue healing, which is promising in soft tissue trauma therapy. STATEMENT OF SIGNIFICANCE: Non-compressible hemorrhage and soft tissue impairment are the main causes of mortality in emergency trauma. Inorganic aerogels with high porosity and outstanding flexibility can rapidly absorb blood to pro-coagulation and fill in irregular trauma without compression, but the low bioactivity limited the ability to promote soft tissue healing. Herein, SiO2-based inorganic nanofiber aerogels (M2+@SiO2, M=Ca, Mg, and Sr) were prepared by freeze-drying the mixture of bioactive silicates-deposited SiO2 nanofibers and SiO2 sol. M2+@SiO2 aerogels possessed high bioactivity and exhibited superior hemostatic performance in compressible and non-compressible bleeding model. Furthermore, Sr2+@SiO2 aerogel showed optimal bioactivities on cell responses and effectively promoted liver healing by releasing bioactive ions and providing highly-interconnected porous support structure for vascular development and tissue regeneration.

Electrochemical stability of electrospun silicon/carbon nanofiber anode materials: a review

Silicon (Si) is regarded as a promising anode material owing to its high specific capacity and low lithiation potential. The large volume change and the pulverization of silicon during the lithiation/delithiation process hinder its direct energy storage application. This review focuses on the electrospun silicon/carbon (Si/C) nanofiber anode materials for lithium-ion batteries for long-term stable energy storage. Silicon is completely embedded in electrospinning-based carbon nanofibers to form electrospun Si/C nanofibers. It not only creates pore space to buffer silicon volume expansion, but also prevents direct contact between silicon and the electrolyte, consequently forming a stable solid electrolyte interface film. The electrospun Si/C nanofibers solve the pulverization issue of silicon to achieve improved cycling stability. Furthermore, the electrospun carbon nanofibers form a flexible conductive network for surrounding silicon by facilely introducing sacrificial polymers or template agents. The electrospun Si/C nanofibers ultimately promote the lithium-ion transport to achieve rate stability. The silicon source selection and microstructure regulation of the electrospun Si/C nanofibers are overviewed. The silicon sources include the direct utilization of silicon or silicon oxide particles as well as the indirect conversion of silicon-based precursors. The cycling stability regulation of various metal- and metal oxide-modified silicon composites and heterogeneous carbon material-decorated electrospun Si/C nanofibers is summarized. In addition, the microstructure designs of the electrospun Si/C nanofibers associated with the improvement of long-term capacity retention are overviewed. The main challenges in the electrospun Si/C nanofiber anode materials are summarized, and the future perspectives are also proposed.

Electrospinning of LaB6/PEDOT:PSS/PEO Fiber Composites of Unique Morphologies

We present a direct electrospinning fabrication technique for the manufacture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylene oxide) (PEDOT:PSS/PEO) polymer fibers containing embedded cubic lanthanum hexaboride (LaB6) particles. We focus on the impact of relative humidity on the formation of uniform polymer fibers and show that a relative humidity of 5% is optimal, resulting in an average fiber thickness of 266 ± 88 nm. As the relative humidity is increased, the fibers contain beads as a consequence of Rayleigh instabilities. The addition of lanthanum hexaboride cubic particles to the polymer solution before electrospinning results in the encapsulation of the LaB6 particles inside the fibers. We investigate the effect of LaB6 particle size on morphology and observe that particles of ∼500 nm yield a fiber-cube-fiber morphology, while 2 μm particles result in fewer embedded cubes along the length of the polymer fibers. This phenomenon likely arises from electrodynamic interactions between the LaB6 particles in the polymer solution and the electric field lines generated during electrospinning between the spinneret and the collector. Our results display the versatility of the electrospinning technique in the fabrication of unique polymer/hexaboride composite fibers.

Research Advances in Electrospun Nanofiber Membranes for Non-Invasive Medical Applications

Non-invasive medical nanofiber technology, characterized by its high specific surface area, biocompatibility, and porosity, holds significant potential in various medical domains, including tissue repair and biosensing. It is increasingly becoming central to healthcare by offering safer and more efficient treatment options for contemporary medicine. Numerous studies have explored non-invasive medical nanofibers in recent years, yet a comprehensive overview of the field remains lacking. In this paper, we provide a comprehensive summary of the applications of electrospun nanofibers in non-invasive medical fields, considering multiple aspects and perspectives. Initially, we introduce electrospinning nanofibers. Subsequently, we detail their applications in non-invasive health, including health monitoring, personal protection, thermal regulation, and wound care, highlighting their critical role in improving human health. Lastly, this paper discusses the current challenges associated with electrospun nanofibers and offers insights into potential future development trajectories.

A systematic review on green and natural polymeric nanofibers for biomedical applications

Electrospinning is the simplest technique to produce ultrathin nanofibers, which enables the use of nanotechnology in various applications. Nanofibrous materials produced through electrospinning have garnered significant attention in biomedical applications due to their unique properties and versatile potential. In recent years, there has been a growing emphasis on incorporating sustainability principles into material design and production. However, electrospun nanofibers, owing to their reliance on solvents associated with significant drawbacks like toxicity, flammability, and disposal challenges, frequently fall short of meeting environmentally friendly standards. Due to the limited solvent choices and heightened concerns for safety and hygiene in modern living, it becomes imperative to carefully assess the implications of employing electrospun nanofibers in diverse applications and consumer products. This systematic review aims to comprehensively assess the current state of research and development in the field of "green and natural" electrospun polymer nanofibers as well as more fascinating and eco-friendly commercial techniques, solvent preferences, and other green routes that respect social and legal restrictions tailored for biomedical applications. We explore the utilization of biocompatible and biodegradable polymers sourced from renewable feedstocks, eco-friendly processing techniques, and the evaluation of environmental impacts. Our review highlights the potential of green and natural electrospun nanofibers to address sustainability concerns while meeting the demanding requirements of various biomedical applications, including tissue engineering, drug delivery, wound healing, and diagnostic platforms. We analyze the advantages, challenges, and future prospects of these materials, offering insights into the evolving landscape of environmentally responsible nanofiber technology in the biomedical field.

Bioinspired self-assembled colloidal collectives drifting in three dimensions underwater

Active matter systems feature a series of unique behaviors, including the emergence of collective self-assembly structures and collective migration. However, realizing collective entities formed by synthetic active matter in spaces without wall-bounded support makes it challenging to perform three-dimensional (3D) locomotion without dispersion. Inspired by the migration mechanism of plankton, we propose a bimodal actuation strategy in the artificial colloidal systems, i.e., combining magnetic and optical fields. The magnetic field triggers the self-assembly of magnetic colloidal particles to form a colloidal collective, maintaining numerous colloids as a dynamically stable entity. The optical field allows the colloidal collectives to generate convective flow through the photothermal effect, enabling them to use fluidic currents for 3D drifting. The collectives can perform 3D locomotion underwater, transit between the water-air interface, and have a controlled motion on the water surface. Our study provides insights into designing smart devices and materials, offering strategies for developing synthetic active matter capable of controllable collective movement in 3D space.

Necklace-Like Nanostructures: From Fabrication, Properties to Applications

The shape-controlled synthesis of nanocrystals remains a hot research topic in nanotechnology. Particularly, the fabrication of 1D structures such as wires, rods, belts, and tubes has been an interesting and important subject within nanoscience in the last few decades. 1D necklace-like micro/nanostructures are a sophisticated geometry that has attracted increasing attention due to their anisotropic and periodic structure, intrinsic high surface area, abundant transport channels, exposure of each component to the surface, and multiscale roughness of the surface. These characteristics enable their unique electrical, optical, and catalytic properties. This review provides a comprehensive summary of the advanced research progress on the fabrication strategies, novel properties, and various applications of necklace-like structures. It begins with the main fabrication methods of necklace-like structures and subsequently details a variety of their properties and applications. It concludes with the authors' perspectives on future research and development of the necklace-like structures.

Designing responsive dressings for inflammatory skin disorders; encapsulating antioxidant nanoparticles into biocompatible electrospun fibres

Inflammatory skin disorders are highly prevalent and current treatments are marred by side-effects. Here, we have designed anti-inflammatory fibrous sheets with the potential to treat low exudate inflammatory skin disorders such as psoriasis or atopic dermatitis. Antioxidant and anti-inflammatory nanoparticles composed of crosslinked poly(propylene sulfide) (PPS) were encapsulated in poly(ethylene oxide) (PEO) fibres via electrospinning from an aqueous suspension. The loading of nanoparticles did not adversely effect the homogenous nature of the electrospun fibres; furthermore, nanoparticles retained their morphology, size and anti-inflammatory character after electrospinning. The PPS-nanoparticle-loaded nanofibres were found to be highly cytocompatible when tested on human dermal fibroblasts. These findings suggest they have significant potential to topically treat inflamed tissues that are characterized by high reactive oxygen species (ROS) levels.

Structural design toward functional materials by electrospinning: A review

Electrospinning as one of the most versatile technologies have attracted a lot of scientists’ interests in past decades due to its great diversity of fabricating nanofibers featuring high aspect ratio, large specific surface area, flexibility, structural abundance, and surface functionality. Remarkable progress has been made in terms of the versatile structures of electrospun fibers and great functionalities to enable a broad spectrum of applications. In this article, the electrospun fibers with different structures and their applications are reviewed. First, several kinds of electrospun fibers with different structures are presented. Then the applications of various structural electrospun fibers in different fields, including catalysis, drug release, batteries, and supercapacitors, are reviewed. Finally, the application prospect and main challenges of electrospun fibers are discussed. We hope that this review will provide readers with a comprehensive understanding of the structural design and applications of electrospun fibers in different fields.

Micromagnetic Simulations of Chaotic Ferromagnetic Nanofiber Networks

Electrospinning can be used to create nanofibers with diameters of typically a few tens to a few hundred nanometers. While pure polymers are often electrospun, it is also possible to use polymer blends or to include nanoparticles. In this way, e.g., magnetic nanofiber networks can be created with a certain diameter distribution, random fiber orientations, and random crossing positions and angles. Here we present for the first time micromagnetic simulations of small parts of stochastically oriented nanofiber networks. Magnetization reversal mechanisms are investigated for different local spatial distributions; mutual influences of neighboring magnetic fibers due to dipolar interactions are depicted. This study serves as a base for the possible use of such stochastic nanofiber networks in the research area of neuro-inspired materials.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Magnetic Nanofiber Mats for Data Storage and Transfer

Electrospun nanofiber mats may serve as new hardware for neuromorphic computing. To enable data storage and transfer in them, they should be magnetic, possibly electrically conductive and able to respond to further external impulses. Here we report on creating magnetic nanofiber mats, consisting of magnetically doped polymer nanofibers for data transfer and polymer beads containing larger amounts of magnetic nanoparticles for storage purposes. Using magnetite and iron nickel oxide nanoparticles, a broad range of doping ratios could be electrospun with a needleless technique, resulting in magnetic nanofiber mats with varying morphologies and different amounts of magnetically doped beads.

Review on Fabrication of Structurally Colored Fibers by Electrospinning

Structural color derived from the physical interactions of photons, with the specific chromatic mechanism differing from that of dyes and pigments, has brought considerable attention by the conducive virtue of being dye-free and fadeless. This has recently become a research hot-spot. Assemblies of colloidal nanoparticles enable the manufacture of periodic photonic nanostructures. In our review, the mechanism of nanoparticle assemblies into structurally colored structures by the electrospinning method was briefly introduced, followed by a comparatively comprehensive review summarizing the research related to photonic crystals with periodically aligned nanostructures constructed by the assembly of colloidal nanoparticles, and the concrete studies concerning the fabrication of well-aligned electrospun nanofibers incorporating with colloidal nanoparticles based on the investigation of relevant factors such as the sizes of colloidal nanoparticles, the weight ratio between colloidal nanoparticles, and the polymer matrix. Electrospinning is expected to be a deserving technique for the fabrication of structurally colored nanofibers while the colloidal nanoparticles can be well confined into aligned arrangement inside nanofibres during the electrospinning process after the achievement of resolving remaining challenges.

Preliminary Study of Ultrasonic Welding as a Joining Process for Electrospun Nanofiber Mats

Electrospinning can be used to create nanofiber mats for diverse applications, from wound dressings and tissue engineering to filters for medical and biotechnological applications. In most of these applications, it is necessary to fix the nanofiber mat on a macroscopic textile fabric, on another nanofiber mat or within a frame to keep it at the desired position. Due to their extremely low thickness and areal mass, however, nanofiber mats are easily destroyed by sewing, and in several situations glued bonds are too thick and not flexible enough. Here we report on ultrasonic welding of polyacrylonitrile nanofiber mats, suggesting this method as a joining process without destruction of the mat morphology for thermoplastic nanofiber mats. A variety of welding patterns results in different adhesion forces between both joined nanofiber mats and different failure mechanisms, with some welding patterns enabling bonding stronger than the mats themselves. Our findings show that ultrasonic welding is a possible joining method for polyacrylonitrile nanofiber mats.

Structural Evolution and Formation Mechanism of the Soft Colloidal Arrays in the Core of PAAm Nanofibers by Electrospun Packing

Electrospinning provides a facile and versatile method for generating nanofibers from a large variety of starting materials, including polymers, ceramic, composites, and micro-/nanocolloids. In particular, incorporating functional nanoparticles (NPs) with polymeric materials endows the electrospun fibers/sheets with novel or better performance. This work evaluates the spinnability of polyacrylamide (PAAm) solution containing thermoresponsive poly(N-isopropylacrylamide-co-tert-butyl acrylate) microgel nanospheres (PNTs) prepared by colloid electrospinning. In the presence of a suitable weight ratio (1:4) of PAAm and PNTs, the in-fiber arrangements of PNTs-electrospun fibers will evolve into chain-like arrays and beads-on-string structures by confining of PAAm nanofibers, and then the free amide groups of PAAm can bind amide moieties on the surfaces of PNTs, resulting in the assembling of PNTs in the cores of PAAm fibers. The present work serves as a reference in the fabrication of novel thermoresponsive hybrid fibers involving functional nanospheres via electrospun packing. The prepared nanofibers with chain-like and thermoresponsive colloid arrays in the cores are expected to have potential application in various fields.

Superhydrophobic, Hybrid, Electrospun Cellulose Acetate Nanofibrous Mats for Oil/Water Separation by Tailored Surface Modification

Electrospun cellulose acetate nanofibers (CA-NF) have been modified with perfluoro alkoxysilanes (FS/CA-NF) for tailoring their chemical and physical features aiming oil-water separation purposes. Strikingly, hybrid FS/CA-NF showed that perfluoro groups are rigidly positioned on the outer surface of the nanofibers providing superhydrophobic characteristic with a water contact angle of ∼155°. Detailed analysis showed that hydrolysis/condensation reactions led to the modification of the acetylated β(1 → 4) linked d-glucose chains of CA transforming it into a superhydrophobic nanofibrous mat. Analytical data have revealed that CA-NF surfaces can be selectively controlled for fabricating the durable, robust and water resistant hybrid electrospun nanofibrous mat. The -OH groups available on the CA structure allowed the basic sol-gel reactions started by the reactive FS hybrid precursor system which can be monitored by spectroscopic analysis. Since alkoxysilane groups on the perfluoro silane compound are capable of reacting for condensation together with the CA, superhydrophobic nanofibrous mat is obtained via electrospinning. This structural modification led to the facile fabrication of the novel oil/water nanofibrous separator which functions effectively demonstrated by hexane/oil and water separation experiments. Perfluoro groups consequently modified the hydrophilic CA nanofibers into superhydrophobic character and therefore FS/CA-NF could be quite practical for future applications like water/oil separators, as well as self-cleaning or water resistant nanofibrous structures.

Current Status of Tissue-Engineered Scaffolds for Rotator Cuff Repair

Rotator cuff tears continue to be at significant risk for re-tear or for failure to heal after surgical repair despite the use of a variety of surgical techniques and augmentation devices. Therefore, there is a need for functionalized scaffold strategies to provide sustained mechanical augmentation during the critical first 12-weeks following repair, and to enhance the healing potential of the repaired tendon and tendon-bone interface. Tissue engineered approaches that combine the use of scaffolds, cells, and bioactive molecules towards promising new solutions for rotator cuff repair are reviewed. The ideal scaffold should have adequate initial mechanical properties, be slowly degrading or non-degradable, have non-toxic degradation products, enhance cell growth, infiltration and differentiation, promote regeneration of the tendon-bone interface, be biocompatible and have excellent suture retention and handling properties. Scaffolds that closely match the inhomogeneity and non-linearity of the native rotator cuff may significantly advance the field. While substantial pre-clinical work remains to be done, continued progress in overcoming current tissue engineering challenges should allow for successful clinical translation.

Versatile Production of Poly(Epsilon-Caprolactone) Fibers by Electrospinning Using Benign Solvents

The electrospinning technique is widely used for the fabrication of micro- and nanofibrous structures. Recent studies have focused on the use of less toxic and harmful solvents (benign solvents) for electrospinning, even if those solvents usually require an accurate and longer process of optimization. The aim of the present work is to demonstrate the versatility of the use of benign solvents, like acetic acid and formic acid, for the fabrication of microfibrous and nanofibrous electrospun poly(epsilon-caprolactone) mats. The solvent systems were also shown to be suitable for the fabrication of electrospun structures with macroporosity, as well as for the fabrication of composite electrospun mats, fabricated by the addition of bioactive glass (45S5 composition) particles in the polymeric solution.

Recent advances in electrospun metal-oxide nanofiber based interfaces for electrochemical biosensing

Synthesis of various electrospun metal-oxide nanofibers and their application towards electrochemical enzymatic and enzyme-free biosensor platforms has been critically discussed.

Electrospun Ultrafine Fiber Composites Containing Fumed Silica: From Solution Rheology to Materials with Tunable Wetting

Fumed silica (FS) particles with hydrophobic (R805) or hydrophilic (A150) surface functionalities are incorporated in polyacrylonitrile (PAN) fibers by electrospinning to produce mats with controlled wettability. Rheological measurements are conducted to elucidate the particle-polymer interactions and characterize the system while microscopic and analytic tools are used to examine FS location within both fibers and films to aid in the fundamental understanding of wetting behavior. Unlike traditional polymers, we find these systems to be gel-like, yet electrospinnable; the fumed silica networks break down into smaller aggregates during the electrospinning process and disperse both within and on the surface of the fibers. Composite nanofiber mats containing R805 FS exhibit an apparent contact angle over 130° and remain hydrophobic over 30 min, while similar mats with A150 display rapid surface-wetting with a static contact angle of ∼30°. Wicking experiments reveal that the water absorption properties can be further manipulated, with R805 FS-impregnated mats taking up only 8% water relative to mat weight in 15 min. In contrast, PAN fibers containing A150 FS absorb 425% of water in the same period, even more than the pure PAN fiber (371%). The vastly different responses to water demonstrate the versatility of FS in surface modification, especially for submicron fibrous mats. The role of fumed silica in controlling wettability is discussed in terms of their surface functionality, placement on nanofibers and induced surface roughness.

Aligned multilayered electrospun scaffolds for rotator cuff tendon tissue engineering

The rotator cuff consists of several tendons and muscles that provide stability and force transmission in the shoulder joint. Whereas most rotator cuff tears are amenable to suture repair, the overall success rate of repair is low, and massive tears are prone to re-tear. Extracellular matrix (ECM) patches are used to augment suture repair, but they have limitations. Tissue-engineered approaches provide a promising solution for massive rotator cuff tears. Previous studies have shown that, compared to nonaligned scaffolds, aligned electrospun polymer scaffolds exhibit greater anisotropy and exert a greater tenogenic effect. Nevertheless, achieving rapid cell infiltration through the full thickness of the scaffold is challenging, and scaling to a translationally relevant size may be difficult. Our goal was to evaluate whether a novel method of alignment, combining a multilayered electrospinning technique with a hybrid of several electrospinning alignment techniques, would permit cell infiltration and collagen deposition through the thickness of poly(ε-caprolactone) scaffolds following seeding with human adipose-derived stem cells. Furthermore, we evaluated whether multilayered aligned scaffolds enhanced collagen alignment, tendon-related gene expression, and mechanical properties compared to multilayered nonaligned scaffolds. Both aligned and nonaligned multilayered scaffolds demonstrated cell infiltration and ECM deposition through the full thickness of the scaffold after only 28days of culture. Aligned scaffolds displayed significantly increased expression of tenomodulin compared to nonaligned scaffolds and exhibited aligned collagen fibrils throughout the full thickness, the presence of which may account for the increased yield stress and Young's modulus of cell-seeded aligned scaffolds along the axis of fiber alignment.

STATEMENT OF SIGNIFICANCE

Rotator cuff tears are an important clinical problem in the shoulder, with over 300,000 surgical repairs performed annually. Re-tear rates may be high, and current methods used to augment surgical repair have limited evidence to support their clinical use due to inadequate initial mechanical properties and slow cellular infiltration. Tissue engineering approaches such as electrospinning have shown similar challenges in previous studies. In this study, a novel technique to align electrospun fibers while using a multilayered approach demonstrated increased mechanical properties and development of aligned collagen through the full thickness of the scaffolds compared to nonaligned multilayered scaffolds, and both types of scaffolds demonstrated rapid cell infiltration through the full thickness of the scaffold.

Hybrid carbon silica nanofibers through sol-gel electrospinning

A controlled sol-gel synthesis incorporated with electrospinning is employed to produce polyacrylonitrile-silica (PAN-silica) fibers. Hybrid fibers are obtained with varying amounts of silica precursor (TEOS in DMF catalyzed by HCl) and PAN. Solution viscosity, conductivity, and surface tension are found to relate strongly to the electrospinnability of PAN-silica solutions. TGA and DSC analyses of the hybrids indicate strong intermolecular interactions, possibly between the -OH group of silica and -CN of PAN. Thermal stabilization of the hybrids at 280 °C followed by carbonization at 800 °C transforms fibers to carbon-silica hybrid nanofibers with smooth morphology and diameter ranging from 400 to 700 nm. FTIR analysis of the fibers confirms the presence of silica in the as-spun as well as the carbonized material, where the extent of carbonization is also estimated by confirming the presence of -C═C and -C═O peaks in the carbonized hybrids. The graphitic character of the carbon-silica fibers is confirmed through Raman studies, and the role of silica in the disorder of the carbon structure is discussed.

Nanoparticles meet electrospinning: recent advances and future prospects

Nanofibres can be fabricated by various methods and perhaps electrospinning is the most facile route. In past years, electrospinning has been used as a synthesis technique and the fibres have been prepared from a variety of starting materials and show various properties. Recently, incorporating functional nanoparticles (NPs) with electrospun fibres has emerged as one of most exciting research topics in the field of electrospinning. When NPs are incorporated, on the one hand the NPs endow the electrospun fibres/mats novel or better performance, on the other hand the electrospun fibres/mats could preserve the NPs from corrosion and/or oxidation, especially for NPs with anisotropic structures. More importantly, electrospinning shows potential applications in self-assembly of nanoscale building blocks for generating new functions, and has some obvious advantages that are not available by other self-assembly methods, i.e., the obtained free-standing hybrid mats are usually flexible and with large area, which is favourable for their commercial applications. In this critical review, we will focus on the fabrication and applications of NPs-electrospun fibre composites and give an overview on this emerging field combining nanoparticles and electrospinning. Firstly, two main strategies for producing NPs-electrospun fibres will be discussed, i.e., one is preparing the NPs-electrospun fibres after electrospinning process that is usually combined with other post-processing methods, and the other is fabricating the composite nanofibres during the electrospinning process. In particular, the NPs in the latter method will be classified and introduced to show the assembling effect of electrospinning on NPs with different anisotropic structures. The subsequent section describes the applications of these NPs-electrospun fibre mats and nanocomposites, and finally a conclusion and perspectives of the future research in this emerging field is given.

All Organic Nanofibers As Ultralight Versatile Support for Triplet-Triplet Annihilation Upconversion

We present a method for the fabrication of ultralight upconverting mats consisting of rigid polymer nanofibers. The mats are prepared by simultaneously electrospinning an aqueous solution of a polymer with pronounced oxygen-barrier properties and functional nanocapsules containing a sensitizer/emitter couple optimized for triplet-triplet annihilation photon upconversion. The optical functionality of the nanocapsules is preserved during the electrospinning process. The nanofibers demonstrate efficient upconversion fluorescence centered at λ_max = 550 nm under low intensity excitation with a continuous wave laser (λ = 635 nm, power = 5 mW). The pronounced oxygen-barrier property of the polymer matrix may efficiently prevent the oxygen penetration so upconversion fluorescence is registered in ambient atmosphere. The demonstrated method can be used for the production of upconverting ultralight porous coatings for sensors or upconverting membranes with freely variable thickness for solar cells.

Hierarchically structured metal oxide/silica nanofibers by colloid electrospinning

We present herein a new concept for the preparation of nanofibrous metal oxides based on the simultaneous electrospinning of metal oxide precursors and silica nanoparticles. Precursor fibers are prepared by electrospinning silica nanoparticles (20 nm in diameter) dispersed in an aqueous solution of poly(acrylic acid) and metal salts. Upon calcination in air, the poly(acrylic acid) matrix is removed, the silica nanoparticles are cemented, and nanocrystalline metal oxide particles of 4-14 nm are nucleated at the surface of the silica nanoparticles. The obtained continuous silica fibers act as a structural framework for metal oxide nanoparticles and show improved mechanical integrity compared to the neat metal oxide fibers. The hierarchically nanostructured materials are promising for catalysis applications, as demonstrated by the successful degradation of a model dye in the presence of the fibers.

Structural evolution of electrospun composite fibers from the blend of polyvinyl alcohol and polymer nanoparticles

Electrospinning provides a versatile method for generating fibrous materials from a large variety of substances, including polymers, composites, proteins, and nano/microcolloids. In particular, the incorporation of nano/microparticles with polymeric materials is beneficial to many of electrospun fibers with multiple functionalities. This report evaluates the spinnability of a polymer solution containing polymer nanoparticles obtained through electrospinning. Tunable structures of electrospun composite fibers were obtained from a blended solution of polyvinyl alcohol (PVA) and polystyrene nanospheres (PSNs). The in-fiber arrangements of polymer nanoparticle fibers, influenced by the PVA:PSN weight ratio, and the viscosity of the blended solution and the size of PSNs were systemically studied. Once PVA was determined to dominate the solution, the diameter of the electrospun PVA fibers was comparable to the diameters of the colloidal particles, which confined the nanospheres into string-on-bead and necklace-like structures. When PSNs occupied a large portion of the solution, PVA wrapped the PSNs, forming a blackberry-like aggregate and a uniform colloidal fiber. The results from the colloid electrospinning serve as references in the creation of novel composite fibers involving various polymer nanoparticles via electrospinning. The obtained composite fibers of the polymers and colloids are expected to have potential application in various areas.

Synthesis of porous carbon balls from spherical colloidal crystal templates

Spherical inverse opal (IO) porous carbon was produced utilizing silica colloidal crystal spheres as templates. The spherical colloidal crystals were obtained through the self-assembly of monodisperse particles inside an emulsion droplet with confined geometry. The templates were inverted using a carbon precursor, phenol-formaldehyde (PF) resol. We demonstrated a two-step synthesis involving the subsequent infiltration of the PF resol precursor into the spherical colloidal crystal template and a one-step synthesis using a silica colloidal solution containing dissolved PF resol. In the former case, the sizes of the IO carbon balls were controlled by the size of the colloidal crystal templates, and diameters of a few micrometers up to 50 μm were obtained. The average diameter of the macropores created by the silica particles was 230 nm. Moreover, meso-/macroporous IO carbon balls were created using block-copolymer templates in the PF resol. In the one-step synthesis, the concentration of PF resol in the colloidal solution controlled the diameter of the IO carbon balls. IO balls smaller than 3 μm were obtained from the direct addition of 5% PF resol. The one-step synthesis produced rather irregular porous structures reflecting the less ordered crystallization processes inside the spherical colloidal crystals. Nitrogen adsorption and cyclic voltammetry measurements were conducted to measure the specific area and electroactive surface area of the IO carbon balls. The specific area of the mesopores-incorporated IO carbon balls was 1.3 times higher than that of bare IO carbon balls. Accordingly, the meso-/macroporous porous carbon balls exhibited higher electrocatalytic properties than the macroporous carbon balls.

Free surface electrospinning of fibers containing microparticles

Many materials have been fabricated using electrospinning, including pharmaceutical formulations, superhydrophobic surfaces, catalysis supports, filters, and tissue engineering scaffolds. Often these materials can benefit from microparticles included within the electrospun fibers. In this work, we evaluate a high-throughput free surface electrospinning technique to prepare fibers containing microparticles. We investigate the spinnability of polyvinylpyrrolidone (PVP) solutions containing suspended polystyrene (PS) beads of 1, 3, 5, and 10 μm diameter in order to better understand free surface electrospinning of particle suspensions. PS bead suspensions with both 55 kDa PVP and 1.3 MDa PVP were spinnable at 1:10, 1:5, and 1:2 PS:PVP mass loadings for all particle sizes studied. The final average fiber diameters ranged from 0.47 to 1.2 μm and were independent of the particle size and particle loading, indicating that the fiber diameter can be smaller than the particles entrained and can furthermore be adjusted based on solution properties and electrospinning parameters, as is the case for electrospinning of solutions without particles.

Facile and large-scale fabrication of anisometric particles from fibers synthesized by colloid-electrospinning

A new top-down approach is proposed to form large amounts of anisometric particles. Multicompartment fibers that present different domains composed of silica nanoparticles and larger polystyrene nanoparticles are fabricated by colloid-electrospinning and are subsequently calcinated and broken. The obtained fibers containing voids are subsequently cut via sonication to yield anisometric particles. It is shown that the majority of the fibers can be broken at the voids.