PLA and PBAT-Based Electrospun Fibers Functionalized with Antibacterial Bio-Based Polymers

Antimicrobial fibers based on biodegradable polymers, poly(lactic acid) (PLA), and poly(butylene adipate-co-terephthalate) (PBAT) are prepared by electrospinning. For this purpose, a biodegradable/bio-based polyitaconate containing azoles groups (PTTI) is incorporated at 10 wt.% into the electrospinning formulations. The resulting fibers functionalized with azole moieties are uniform and free of beads. Then, the accessible azole groups are subjected to N-alkylation, treatment that provides cationic azolium groups with antibacterial activity at the surface of fibers. The positive charge density, roughness, and wettability of the cationic fibers are evaluated and compared with flat films. It is confirmed that these parameters exert an important effect on the antimicrobial properties, as well as the length of the alkylating agent and the hydrophobicity of the matrix. The quaternized PLA/PTTI fibers exhibit the highest efficiency against the tested bacteria, yielding a 4-Log reduction against S. aureus and 1.7-Log against MRSA. Then, biocompatibility and bioactivity of the fibers are evaluated in terms of adhesion, morphology and viability of fibroblasts. The results show no cytotoxic effect of the samples, however, a cytostatic effect is appreciated, which is ascribed to the strong electrostatic interactions between the positive charge at the fiber surface and the negative charge of the cell membranes.     

Solvent Vapor Annealing: An Efficient Approach for Inscribing Secondary Nanostructures onto Electrospun Fibers

Solvent vapor annealing (SVA) is originally developed to attain equilibrium nanostructures from microphase‐separated block polymer thin films. Interestingly, by carefully choosing a solvent vapor that can selectively mobilize the amorphous chains of a semicrystalline polymer while preserving the integrity of its crystalline structure, this study demonstrates that the SVA method can also be utilized to introduce hierarchical structures onto semicrystalline polymer‐based materials. This study on electrospun poly(ε‐caprolactone) (PCL) fibers clearly shows that acetone, a poor solvent for PCL, can effectively delocalize the amorphous chains and redeposit them onto the pre‐existing crystal edges, giving rise to secondary nanostructures inscribed onto the PCL fibers. In the past decade, various fiber fabrication methods and numerous fiber products are reported. The easy one‐step approach reported here provides new insight into the design and fabrication of structurally hierarchical polymeric materials.

     

Photo‐Induced Solid‐State Crosslinking of Electrospun Poly(vinyl alcohol) Fibers

Summary: Poly(vinyl alcohol) (PVA) was derivatized by polymer analogous reaction with thienyl acryloyl chloride and processed to submicrometer fibers by electrospinning from aqueous solution. Water solubility of otherwise water‐soluble PVA fibers was reduced considerably by UV crosslinking of thienyl acrylate modified PVA fibers in the solid state. Water stability of these crosslinked fibers was proven by water steam test at 95 °C.

UV/Vis spectrum of PVA‐Thio fibers irradiated for different periods at 300 nm.     

Electrospun Cu-Deposited Flexible Fibers as an Efficient Oxygen Evolution Reaction Electrocatalyst

Developing oxygen evolution reaction (OER) catalysts with high activity, long-term durability, and at low cost remains a great challenge. Herein, we report the high activity of fibrous Cu-based catalysts. The synthesis process is simple and scalable. Electrospinning method was selected to synthesize fibrous polymer substrates (Poly(vinylidene fluoride-co-hexafluoropropylene, PVdF-HFP), which are then covered by Cu via electroless deposition. Cu-deposited PVdF-HFP with different microstructures having smooth and roughened surfaces were also synthesized by drop-casting and impregnation method, respectively, to emphasize the importance of the microstructures on OER activity. The OER activity and durability were studied by linear sweep voltammetry, chronoamperometry, and Tafel slope analysis. The Cu/PVdF-HFP fibrous catalysts exhibit significantly improved OER activity and durability compared with Cu plate as well as Cu-deposited PVdF-HFP with different microstructures. The unique fibrous structure provides better mass transport, diffusion, and large active surface area. In addition to the advantages of the fibrous structure, attenuated total reflection infrared (ATR-IR) and ex situ X-ray photoelectron spectroscopy revealed that the improved specific activity for Cu/PVdF-HFP fiber can be attributed to the synergistic effect between Cu and Cu/PVdF-HFP (electron transfer from Cu to PVdF-HFP) at the Cu|PVdF-HFP interface, which results in optimized reaction energetics for the OER.     

电纺纤维在超级电容器中的应用

对高性能超级电容器不断增长的需求促进了电极隔膜和电极材料的快速发展.静电纺丝法制备的纳米纤维具有较高的孔隙率、较好电化学活性、较大的表面积以及良好的结构稳定性等优点,已被广泛应用于超级电容器的隔膜和电极材料.本文简要综述了近年来电纺纳米纤维在超级电容器用隔膜和电极材料的研究进展;着重讨论了通过静电纺丝和其他后处理方法制...     

Morphological Characterization of Electrospun Nano-Fibrous Membranes of Biodegradable Poly(L-lactide) and Poly(lactide-co-glycolide)

Hydrophobic biodegradable polyesters, poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA), were electrospun on different types of collectors to induce morphological changes in the nanofibrous membrane. On the metal collector smooth nonwoven membranes were obtained for both PLLA and PLGA, while on the water reservoir the surface of the membranes became rough due to shrinkage and slow charge dissipation. When NaCl was added to water to enhance the conductivity, the roughness of the membrane surface was changed, yet the shrinkage remained relatively unchanged. The crystallization of PLLA electospun material on the metal plate was suppressed because of the rapid solvent evaporation, however, upon annealing above the glass transition temperature for 24 hr the PLLA membrane became crystallized. When electrospun on the water reservoir, the PLLA membrane remained amorphous. Crystalline PLLA was obtained by electrospinning on the methanol reservoir due to the swelling of nanofibers by methanol.     

Evaluation of Electrospun PCL-PLGA for Sustained Delivery of Kartogenin

In this study, kartogenin was incorporated into an electrospun blend of polycaprolactone and poly(lactic-co-glycolic acid) (1:1) to determine the feasibility of this system for sustained drug delivery. Kartogenin is a small-molecule drug that could enhance the outcome of microfracture, a cartilage restoration procedure, by selectively stimulating chondrogenic differentiation of endogenous bone marrow mesenchymal stem cells. Experimental results showed that kartogenin did not affect the electrospinnability of the polymer blend, and it had negligible effects on fiber morphology and scaffold mechanical properties. The loading efficiency of kartogenin into electrospun membranes was nearly 100%, and no evidence of chemical reaction between kartogenin and the polymers was detected by Fourier transform infrared spectroscopy. Analysis of the released drug using high-performance liquid chromatography–photodiode array detection indicated an abundance of kartogenin and only a small amount of its major hydrolysis product. Kartogenin displayed a typical biphasic release profile, with approximately 30% being released within 24 h followed by a much slower, constant rate of release up to 28 days. Although additional development is needed to tune the release kinetics and address issues common to electrospun scaffolds (e.g., high fiber density), the results of this study demonstrated that a scaffold electrospun from biodegradable synthetic polymers is a suitable kartogenin delivery vehicle.     

Electrospun polystyrene fibers for HIV entrapment

The high versatility and ease of electrospinning of polymer solutions have recently resulted in electrospun fibers, which are of interest for a wide variety of chemical and biomedical applications. This is partially due to the high surface area of the fibers, which is attractive for the detection and capture of (bio)chemicals. In the present work, polystyrene (PS) fibers were electrospun and coated with cationic poly(allylamine hydrochloride) (PAH) or anionic dextran sulfate sodium (DSS). The fibers were physicochemically characterized. Upon incubation in a dispersion of inactivated HIV‐1, avid binding of HIV to all types of fibers occurred. By atomic force microscopy and spatial selective photobleaching, the binding of the inactivated HIV‐1 particles to the fibers could be confirmed. Interestingly, all fibers, especially the DSS‐coated and PAH‐coated ones, resulted in a significant reduction of infection of CD4⁺ TZMbl cells by replication‐competent HIV‐1. On top, DSS‐coated PS fibers were not toxic for vaginal epithelial cells, which may make these fibers of potential interest to inhibit HIV infection in the context of topical prevention. Copyright © 2014 John Wiley & Sons, Ltd.     

The Mechanical Deformation Process of Electrospun Polymer Nanocomposite Fibers

Summary: The mechanical deformation processes of poly(methyl methacrylate)/ montmorillonite nanocomposites and their electrospun fibers were investigated by in situ tensile tests under a transmission electron microscope depending on their morphology. While the polymer nanocomposites deformed in a brittle manner, i.e., crazing, the electrospun polymer nanocomposite fibers deformed through a shear flow process leading to “nanonecking” due to the strong overlap of stress fields caused by nanopores within the fiber under a uniaxial tensile load. This unique change in deformation behavior provides the possibility that the intrinsic brittle material could be manipulated to be ductile without sacrificing its other attractive properties through a well‐controlled electrospinning process.

TEM micrograph of a low temperature fractured fiber showing the nanoporous surface structure.     

Mimetics of Eggshell Membrane Protein Fibers by Electrospinning

Summary: Mimetics of eggshell membrane protein fibers have been obtained with an electrospinning technique based on soluble eggshell membrane protein (SEP) prepared previously. Poly(ethylene oxide), a biocompatible and water soluble polymer, is used to improve the processability of SEP. Blends of SEP/PEO aqueous solutions were electrospun. The diameters of the fibers are 0.3–20 μm depending on the concentration of the solution and the proportion of SEP/PEO. Two “cross‐linking” methods are investigated in order to improve the anti‐water property of the fibers.

Scanning electron micrograph of electrospun fibers.     

Ultrafine Electrospun Conducting Polymer Blend Fibers and Their Photoluminescence Properties

Ultrafine poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene) (MEH-PPV)/polyvinylpyrrolidone (PVP) blend fibers with the average diameters ranging from 625 nm to 1.46 µm were prepared by electrospinning of polymer blend solutions in the mixed solvent of chlorobenzene and methanol. The average diameter of fibers was found to decrease with initial increase in the applied electrical potential and composition of MEH-PPV, reach a minimum value at an intermediate value, and increase with further increase in the applied electrical potential and composition of MEH-PPV, while it was found to decrease with increasing collection distance. PVP was easily removed from MEH-PPV/PVP fibers by the Soxhlet extraction, and after the removal of PVP at high composition of MEH-PPV, pure MEH-PPV fibers were obtained as a ribbon-like structure aligned with wrinkled surface in fiber direction. The increase in MEH-PPV composition and the removal of PVP from as-spun MEH-PPV/PVP fibers resulted in a significant blue-shift in UV-Vis absorption peak and red-shift in PL peak.     

Morphology Tuning of Electrospun Liquid Crystal/Polymer Fibers

This paper elucidates the means to control precisely the morphology of electrospun liquid crystal/polymer fibers formed by phase separation. The relative humidity, solution parameters (concentration, solvent), and the process parameter (feed rate) were varied systematically. We show that the morphology of the phase‐separated liquid crystal can be continuously tuned from capsules to uniform fibers with systematic formation of beads‐on‐a‐string structured fibers in the intermediate ranges. In all cases, the polymer forms a sheath around a liquid‐crystal (LC) core. The width of the polymer sheath and the diameter of the LC core increase with increasing feed rates. This is similar to the results obtained by coaxial electrospinning. Because these fibers retain the responsive properties of liquid crystals and because of their large surface area, they have potential applications as thermo‐, chemo‐, and biosensors. Because the size and shape of the liquid‐crystal domains will have a profound effect on the performance of the fibers, our ability to precisely control morphology will be crucial in developing these applications.     

Annealing Effect on Electrospun Polymer Fibers and Their Transformation into Polymer Microspheres

Electrospinning is a simple and convenient technique to produce polymer fibers with diameters ranging from several nanometers to a few micrometers. Different types of polymer fibers have been prepared by electrospinning for various applications. Among different post‐treatment methods of electrospun polymer fibers, the annealing process plays a critical role in controlling the fiber properties. The morphology changes of electrospun polymer fibers under annealing, however, have been little studied. Here we investigate the annealing effect of electrospun poly(methyl methacrylate) (PMMA) fibers and their transformation into PMMA microspheres. PMMA fibers with an average size of 2.39 μm are first prepared by electrospinning a 35 wt% PMMA solution in dimethylformamide. After the electrospun fibers are thermally annealed in ethylene glycol, a non‐solvent for PMMA, the surfaces of the fibers undulate and transform into microspheres driven by the Rayleigh instability. The driving force of the transformation process is the minimization of the interfacial energy between the polymer fibers and ethylene glycol. The sizes of the microspheres fit well with the theoretical predictions. Longer annealing times are found to be required at lower temperatures to obtain the microspheres.     

可控核/壳结构聚合物电纺纤维的制备与应用

核/壳结构纳米纤维是一种兼具核层与壳层优异性能的功能化复合纤维, 通常具有优于核层和壳层自身的性能, 如可控的机械强度和较好的热传导系数等。其特殊的结构极大地提高了纤维的使用价值, 拓宽了纤维的应用领域, 因此, 核/壳结构纳米纤维成为纤维领域的研究热点之一。静电纺丝技术因其简单有效的特点, 近些年来在众多纳米纤维制备技术中一直备受关注, 制备结构和形貌可控的核/壳结构纤维的方法对于指导其在实际中的应用尤为重要。本文系统介绍了以静电纺丝技术制备核/壳结构纳米纤维的方法, 主要包括单喷头相分离法、同轴静电纺丝法、乳液静电纺丝法以及模板法, 重点讨论了影响核/壳结构的主要因素以及核/壳结构对纤维性能的影响。综述了近几年来国内外关于可控核/壳结构电纺纤维制备的研究新进展及其在药物缓释体系、组织工程支架、多功能敷料、污水处理材料、疏水性材料等领域的潜在应用价值。     

溶胶-凝胶涂附电纺纳米纤维制备ZrO2纳米管

Stable zirconia sol was prepared using inorganic salt(zirconia chloride octahydrate) as the precursor and H₂O₂ as the catalyst. ZrO₂-PBS coaxial nanofibers were fabricated using the sol-gel coating technique to filling poly butylenes succinate(PBS) fibers with zirconium dioxide by electrospun. ZrO₂ nanotubes were obtained via calcining ZrO₂-PBS coaxial nanofibers. The ZrO₂ nanotubes were characterized by TG, SEM and TEM, respectively. The results show that ZrO₂ nanotubes with a diameter of 50～100 nm are obtained after calcining ZrO₂-PBS coaxial nanofibers at 450 ℃.     

The Enhanced Encapsulation Capacity of Polyhedral Oligomeric Silsesquioxane‐based Copolymers for the Fabrication of Electrospun Core/Shell Fibers

This paper reports the use of polyhedral oligomeric silsesquioxane (POSS)‐based copolymers to stabilize the core/shell interface for the facile fabrication of electrospun core/shell fibers. For the poly[(propylmethacryl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane)‐co‐(methyl methacrylate)] (POSS‐MMA)/poly(ε‐caprolactone) (PCL) system, the bicontinuity of hybrid core/shell fibers can be tuned by controlling the phase separation of POSS‐MMA/PCL in electrospinning solutions and therefore the size of PCL‐in‐POSS‐MMA emulsion droplets. Our results demonstrate the enhanced encapsulation capacity of POSS‐MMA copolymers as shell materials. Taking advantage of the rapid advancement of POSS‐based copolymer synthesis, this study can potentially be generalized to guide the fabrication of various other POSS‐based core/shell nano‐/microstructures by using single‐nozzle electrospinning or coaxial electrospinning.

     

Effect of Thermal Annealing on the Surface Properties of Electrospun Polymer Fibers

Electrospun polymer fibers are gaining importance because of their unique properties and applications in areas such as drug delivery, catalysis, or tissue engineering. Most studies to control the morphology and properties of electrospun polymer fibers focus on changing the electrospinning conditions. The effects of post‐treatment processes on the morphology and properties of electrospun polymer fibers, however, are little studied. Here, the effect of thermal annealing on the surface properties of electrospun polymer fibers is investigated. Poly(methyl methacrylate) and polystyrene fibers are fist prepared by electrospinning, followed by thermal annealing processes. Upon thermal annealing, the surface roughness of the electrospun polymer fibers decreases. The driving force of the smoothing process is the minimization of the interfacial energy between polymer fibers and air. The water contact angles of the annealed polymer fibers also decrease with the annealing time.

     

Solvent Influences the Morphology and Mechanical Properties of Electrospun Poly(L-lactic acid) Scaffold for Tissue Engineering Applications

Electrospun micro- and nanofiber scaffolds have gained interest in biomedical applications, especially in tissue engineering, because they can be used to reproduce the structure of the extracellular matrix (ECM) of natural tissue. The selection of the solvent is an important factor which affects the diameter, the surface morphology and the crystallinity of the electrospun fibers, and, accordingly, their mechanical properties as well as their degradation kinetics. Furthermore, the surface morphology of the electrospun fibres can be controlled by solvent vapour pressure to produce porous structures which might be helpful for cell adhesion and proliferation. In the present work, poly (L-lactic acid) (PLLA) has been electrospun using solvents with different vapour pressures to investigate the influences of the solvent vapour pressure on morphology, diameter, crystallinity and mechanical properties of the electrospun fiber scaffolds. The results show that the vapour pressure of the solvents (or solvent mixtures) play an important role in the fiber diameter and crystallinity. Furthermore, the crystallinity of the fibers is increased by lowering the vapour pressure of the used solvent. In addition, the mechanical properties (e.g., tensile strength and Young's modulus) are strongly dependent on morphological features such average fibers diameter. The smaller the average diameter, the higher the tensile strength and Young's modulus.