Electrospun carbon nanofibers as low-cost counter electrode for dye-sensitized solar cells

Electrospun carbon nanofibers (ECNs) have been explored as an electrocatalyst and low-cost alternative to platinum (Pt) for triiodide reduction in dye-sensitized solar cells (DSCs). The results of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements indicated that the ECN counter electrodes exhibited low charge-transfer resistance (Rct), large capacitance (C), and fast reaction rates for triiodide reduction. Although the efficiency (η) of ECN-based cells was slightly lower than that of Pt-based cells, their short circuit current density (Jsc) and open circuit voltage (Voc) were comparable. The ECN-based cells achieved an energy conversion efficiency (η) of 5.5 % under the AM 1.5 illumination at 100 mW cm(-2). The reason for lower cell performance using the ECN electrode was because of its lower fill factor (FF) than that of Pt-based cells, probably caused by high total series resistance (RStot) at ～15.5 Ω cm2, which was larger than that of ～4.8 Ω cm2 in the Pt-based devices. Simulated results showed that the fill factor (FF) and η could be substantially improved by decreasing RStot, which might be achieved by using thinner and highly porous ECNs to reduce the thickness of the ECNs counter electrode.     

Electrospun chitosan/PEDOT nanofibers

Plasma-modified chitosan and poly(3,4-ethylenedioxythiophene) were blended to obtain conducting nanofibers with polyvinyl alcohol as a supporting polymer at various volumetric ratios by electrospinning method. Chemical compositions and molecular interactions among nanofiber blend components were determined using Fourier transform infrared spectroscopy (FTIR). The conducting blends containing plasma-modified chitosan resulted in a superior antibacterial activity and thinner fiber formation than those containing chitosan without plasma-modification. The obtained nanofiber diameters of plasma-modified chitosan were in the range of 170 to 200 nm and those obtained from unmodified chitosan were in the range of 190 to 246 nm. The electrical and electrochemical properties of nanofibers were also investigated by four-point probe conductivity and cyclic voltammetry measurements.     

Electrospun chitosan/hydroxyapatite nanofibers for bone tissue engineering

Chitosan (CS) nanofibers were prepared by an electrospinning technique and then treated with simulated body fluid (SBF) to encourage hydroxyapatite (HA) formation on their surface. The CS/HA nanofibers were subjected to scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy, and X-ray diffraction (XRD) to confirm HA formation as well as determine the morphology of the nanofibrous scaffolds. The SEM image indicated that the distribution of HA on the CS nanofibers was homogeneous. The results from EDS and XRD indicated that HA was formed on the nanofibrous surfaces after 6-day incubation in the SBF. The calcium/phosphorus ratio of deposited HA was close to that of natural bone. To determine biocompatibility, the CS/HA scaffolds were applied to the culture of rat osteosarcoma cell lines (UMR-106). The cell densities on the CS/HA nanofibers were higher than those on the CS nanofibers, the CS/HA film, and the CS film, indicating that cell proliferation on CS/HA nanofibers was enhanced. Moreover, the early osteogenic differentiation on CS/HA was also more significant, due to the differences in chemical composition and the surface area of CS/HA nanofibers. The biocompatibility and the cell affinity were enhanced using the CS/HA nanofibers. This indicates that electrospun CS/HA scaffolds would be a potential material in bone tissue engineering.     

Electrospun nanofibers immobilized with collagen for neural stem cells culture

Fibrous mats via electrospinning have been widely applied in tissue engineering. In this work, nanofibers were prepared via electrospinning from polymer with different content of carboxyl groups. A natural material, collagen, was then immobilized onto the nanofiber surface by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC)/N-Hydroxysuccinimide (NHS) activation process. It was found that the immobilization degree of collagen could be facilely modulated. The obtained collagen-modified nanofibers were used for neural stem cells culture, and unmodified nanofibers were used as a control. Results indicated that the modification of collagen could enhance the attachment and viability of the cultured neural stem cells.     

Electrospun composite nanofibers for tissue regeneration

Nanotechnology assists in the development of biocomposite nanofibrous scaffolds that can react positively to changes in the immediate cellular environment and stimulate specific regenerative events at molecular level to generate healthy tissues. Recently, electrospinning has gained huge momentum with greater accessibility of fabrication of composite, controlled and oriented nanofibers with sufficient porosity required for effective tissue regeneration. Current developments include the fabrication of nanofibrous scaffolds which can provide chemical, mechanical and biological signals to respond to the environmental stimuli. These nanofibers are fabricated by simple coating, blending of polymers/bioactive molecules or by surface modification methods. For obtaining optimized surface functionality, with specially designed architectures for the nanofibers (multi-layered, core-shell, aligned), electrospinning process has been modified and simultaneous 'electrospin-electrospraying' process is one of the most lately introduced technique in this perspective. Properties such as porosity, biodegradation and mechanical properties of composite electrospun nanofibers along with their utilization for nerve, cardiac, bone, skin, vascular and cartilage tissue engineering are discussed in this review. In order to locally deliver electrical stimulus and provide a physical template for cell proliferations, and to gain an external control on the level and duration of stimulation, electrically conducting polymeric nanofibers are also fabricated by electrospinning. Electrospun polypyrrole (PPy) and polyaniline (PAN) based scaffolds are the most extensively studied composite substrates for nerve and cardiac tissue engineering with or without electrical stimulations, and are discussed here. However, the major focus of ongoing and future research in regenerative medicine is to effectively exploit the pluripotent potential of Mesenchymal Stem Cell (MSC) differentiation on composite nanofibrous scaffolds for repair of organs.     

Electrospun nanofibers as a platform for multifunctional,hierarchically organized nanocomposite

Nanofibers are ideally suited to form a scaffold where multi-functional components can be hierarchically organized. Development in electrospinning in terms of fiber construction and organization, materials selection and incorporation, and post-spinning modifications have pathed the way for future developments of advanced composite systems. A nanocomposite system with up to five distinct levels of organization can be constructed using electrospun fibers. At the first level is a composite nanofiber. The second level is a second layer of composite material coated over the core composite nanofiber. Surface modification of the nanofiber will give the third level. The fourth level of organization is by arranging the nanofibers to form an assembly. Finally at the last level, the nanofiber assembly can be encapsulated within a matrix or form a bulk structure of a pre-determined shape. Examples of how hierarchically organized multifunctional nanocomposite can be used in healthcare, environmental and defense and security is discussed.     

Nanocomposites of PLA and PCL based on montmorillonite and sepiolite

PLA and PCL nanocomposites prepared by adding two organically modified montmorillonites and one sepiolite were obtained by melt blending. Materials were characterized by Wide Angle X-ray analysis (WAXS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic-Mechanical Thermal Analysis (DMTA).All clays showed a good dispersion level with both polymeric matrices, whilst the highest thermo-mechanical improvements were reached depending on type of clay. These improvements were considerably higher in the case of PLA based nanocomposites probably because of a higher polymer/filler compatibility.     

Electrospun porous nanofibers for electrochemical energy storage

The demand for energy storage systems is rising due to the rapid development of electric transportation vehicles, and this demand is stimulating research on the next generation of high-performance, high-density energy storage devices. In this work, nanomaterials with excellent electrochemical properties are of particular significance. This review summarizes a variety of methods based on electrospinning techniques for the preparation of porous nanofibers with controllable morphologies. An emphasis is placed on methods involving polymer templates and polymer blend templates, hard templates, and on solvent-induced, nonsolvent-induced or activation methods. As a simple and cost-effective method for preparing one-dimensional nanomaterials, the electrospinning technique is of special significance in the energy storage field, because the as-prepared porous nanofibers exhibit large specific surface areas and interconnected micro-/meso-/macroporous structures. Both of these features enable greater energy storage. Furthermore, this review presents several suggestions for meeting the challenges involved in the preparation and industrial application of electrospun porous nanofibers for advanced energy storage systems.     

Electrospun polyvinyl alcohol-collagen-hydroxyapatite nanofibers: a biomimetic extracellular matrix for osteoblastic cells

The failure of prosthesis after total joint replacement is due to the lack of early implant osseointegration. In this study polyvinyl alcohol-collagen-hydroxyapatite (PVA-Col-HA) electrospun nanofibrous meshes were fabricated as a biomimetic bone-like extracellular matrix for the modification of orthopedic prosthetic surfaces. In order to reinforce the PVA nanofibers, HA nanorods and Type I collagen were incorporated into the nanofibers. We investigated the morphology, biodegradability, mechanical properties and biocompatibility of the prepared nanofibers. Our results showed these inorganic-organic blended nanofibers to be degradable in vitro. The encapsulated nano-HA and collagen interacted with the PVA content, reinforcing the hydrolytic resistance and mechanical properties of nanofibers that provided longer lasting stability. The encapsulated nano-HA and collagen also enhanced the adhesion and proliferation of murine bone cells (MC3T3) in vitro. We propose the PVA-Col-HA nanofibers might be promising modifying materials on implant surfaces for orthopedic applications.     

Electrospun carbon-tin oxide composite nanofibers for use as lithium ion battery anodes

Composite carbon-tin oxide (C-SnO(2)) nanofibers are prepared by two methods and evaluated as anodes in lithium-ion battery half cells. Such an approach complements the long cycle life of carbon with the high lithium storage capacity of tin oxide. In addition, the high surface-to-volume ratio of the nanofibers improves the accessibility for lithium intercalation as compared to graphite-based anodes, while eliminating the need for binders or conductive additives. The composite nanofibrous anodes have first discharge capacities of 788 mAh g(-1) at 50 mA g(-1) current density, which are greater than pure carbon nanofiber anodes, as well as the theoretical capacity of graphite (372 mAh g(-1)), the traditional anode material. In the first protocol to fabricate the C-SnO(2) composites, tin sulfate is directly incorporated within polyacrylonitrile (PAN) nanofibers by electrospinning. During a thermal treatment the tin salt is converted to tin oxide and the polymer is carbonized, yielding carbon-SnO(2) nanofibers. In the second approach, we soak the nanofiber mats in tin sulfate solutions prior to the final thermal treatment, thereby loading the outer surfaces with SnO(2) nanoparticles and raising the tin content from 1.9 to 8.6 wt %. Energy-dispersive spectroscopy and X-ray diffraction analyses confirm the formation of conversion of tin sulfate to tin oxide. Furthermore, analysis with Raman spectroscopy reveals that the additional salt soak treatment from the second fabrication approach increases in the disorder of the carbon structure, as compared to the first approach. We also discuss the performance of our C-SnO(2) compared with its theoretical capacity and other nanofiber electrode composites previously reported in the literature.     

PLA/PCL共混膜的制备及性能研究

目的研究PCL含量对PLA/PCL共混包装膜性能的影响,以改善PLA的韧性。方法将不同质量比的PLA和PCL树脂均匀混合,而后熔融挤出吹膜制得PLA/PCL共混膜。对制得的共混膜进行力学性能测试,获得拉伸强度和断裂伸长率,再通过扫描电镜分析观察其微观断面,采用DSC测试分析其熔融结晶行为,通过氧气透过性能和透湿性能的测试获得其阻隔性能。结果通过扫描电镜与红外光谱发现,PLA与PCL为两相结构,界面不相容;力学性能显示当PCL的质量少于20%时,对PLA的增韧效果不明显;当PCL的质量为50%时,PLA的断裂伸长率从2.9%提高到290%;DSC结果发现,PCL的加入有助于降低PLA的玻璃化转变温度,提高结晶度;阻隔性能结果表明,随着PCL质量比的增大,共混膜的氧气透过系数和透湿系数下降,阻隔性得到提高。结论 PCL的加入能提高PLA的韧性,当PCL与PLA质量比为3∶7时,共混膜具有最佳的性能。     

Electrospun sandwich configuration nanofibers as transparent membranes for skin care drug delivery systems

The development of biocompatible nanocomposites for biomedical applications such as drug release has attracted increasing attention in recent years. In this work, electrospun membranes composed of polycaprolactone (PCL) and shellac were fabricated because PCL has favorable mechanical and biological properties, such as high biocompatibility and biodegradability. Meanwhile, shellac is biocompatible and non-toxic; as a result, the fabricated membranes are attractive for controlled drug delivery. Here, PCL/shellac/PCL nanofiber membranes were treated by ethanol vapor to improve their properties for use in drug delivery applications. Salicylic acid was loaded in the drug delivery system as a model drug, and three PCL/shellac/PCL membrane configurations were investigated. Ethanol vapor treatment increased the tensile strength, flexibility, and transparency of the membranes. Both the tensile strength and drug release properties of the membranes strongly depended on the ratio of PCL to shellac.     

可生物降解PLA／PCL,PELA／PECL共混体系的研究

本工作以DSC研究了聚d,l-乳酸/聚ε-己内酯(PLA/PCL)、聚d,l-乳酸-聚乙二醇嵌段共聚物/聚ε-己内酯-聚乙二醇嵌段共聚物(PELA/PECL)共混体系的相容性,发现PLA/PCL体系是不相容的,随PLA含量的增大,PCL结晶度增大。而PELA/PECL共混体系中,由于PEG链段的“内增容作用”,使二组分有较好的相容性。随PELA含量的增加,PECL的熔点、结晶度降低。     

聚己内酯/羟基磷灰石晶须复合多孔支架的研究

采用溶液浇铸法,以二氯甲烷作为溶剂,制备了聚己内酯/羟基磷灰石晶须(PCL/HAw)复合多孔支架,并进行了正交试验,综合分析了不同配方量的PCL和HAw对材料机械性能的影响。结果表明,可通过控制PCL的量来控制支架的力学性能,通过加入HAw提高支架的亲水性能,支架的接触角实验显示其接触角为81°;PCL的结晶度会随着HAw含量的增加而增强,复合多孔支架的抗拉强度为1.43M~9.21MPa,并在PCL与HAw的质量比为100∶3时达到最大;细胞毒性实验显示,PCL/HAw复合多孔支架细胞毒性为0,满足生物材料使用要求。     

Preparation of chitosan/PLA blend micro/nanofibers by electrospinning

The chitosan/PLA blend micro/nanofibers have been prepared for the first time by electrospinning. Trifluoroacetic acid (TFA) was found to be the co-solvent for electrospinning. The chitosan/PLA blend solutions in various ratios were studied for electrospinning into micro/nanofibers. The morphology of the fibers was shown by scanning electron microscope (SEM). It was found that the average diameter of the chitosan/PLA blend fibers became larger, and the morphology of the fibers became finer with the content of PLA increasing. To show the molecular interactions, chitosan/PLA fibers were characterized by Fourier transform infrared spectroscopy (FTIR). The spun micro/nanofibers are expected to be used in the native extracellular matrix for tissue engineering.     

Blow-spun chitosan/PEG/PLGA nanofibers as a novel tissue engineering scaffold with antibacterial properties

Blow spinning is continuing to gain attention in tissue engineering, as the resultant nanofibrous structures can be used to create a biomimetic environment. In this study, blow spinning was used to construct nanofiber scaffolds with up to 10?% chitosan and poly(DL-lactide-co-glycolide) in the absence or presence of poly(ethylene glycol). Scanning electron microscopy demonstrated that nanofibers were distributed randomly to form three-dimensional mats. With respect to chitosan concentration, the average fiber diameter did not differ statistically in either the absence or presence of poly(ethylene glycol). In poly(ethylene glycol)-formulations, the average fiber diameter ranged from (981.9?±?611.3) nm to (1139.2?±?814.2) nm. In vitro cellular metabolic activity and proliferation studies using keratinized rat squamous epithelial cells (RL-65) showed that cytocompatibility was not compromised with the addition of poly(ethylene glycol). The cell responses at lower (1 and 2.5?%) chitosan concentrations were not significantly different from the groups without chitosan or no scaffold when cultivated for 3, 6, or 9 days. However, >15?% reduction in cellular responses were observed at 10?% chitosan. In presence of poly(ethylene glycol), nearly a 1-log incremental reduction in the number of colony forming units of Streptococcus mutans occurred as the chitosan concentration increased from 0–1 to 2.5?%. Bacterial preparations tested with poly(ethylene glycol) and 5 or 10?% chitosan were not significantly different than the positive kill control. Taken together, the most favorable conditions for attaining cytocompatibility and maintaining antibacterial functionality existed in poly(ethylene glycol)/poly(DL-lactide-co-glycolide) blow-spun scaffolds with integrated 1 or 2.5?% chitosan.     

HA/PLA复合材料界面相互作用及其力学性能的MD模拟

基于HA/PLA复合材料可以在很大程度上实现HA与PLA两者的优势互补,有望成为一种理想的骨替换材料。运用分子动力学(MD)方法,从分子理论的角度研究了羟基磷灰石(HA)的3个晶面(001)、(100)、(110)分别与聚乳酸(PLA)相互作用后混合体系的结合能,并对(110)晶面径向分布函数和力学性能进行了计算分析。结果表明,3晶面所对应结合能大小为HA(110)>HA(100)>HA(001);其相互作用主要源自PLA中的O原子分别与HA中的H原子形成的氢键以及Oa1—Ca之间形成了离子键;PLA组分能够对HA的力学性能起到明显的加强作用,且HA/PLA混合体系在各个方向的力学性能较单组分HA更为接近,从而克服了因材料各向异性而导致的缺陷。     

In vitro evaluation of electrospun PCL/nanoclay composite scaffold for bone tissue engineering

Polycaprolactone (PCL) is a widely accepted synthetic biodegradable polymer for tissue engineering, however its use in hard tissue engineering is limited because of its inadequate mechanical strength and low bioactivity. In this study, we used halloysite nanoclay (NC) as an inorganic filler material to prepare PCL/NC fibrous scaffolds via electrospinning technique after intercalating NC within PCL by solution intercalation method. The obtained nanofibrous mat was found to be mechanically superior to PCL fibrous scaffolds. These scaffolds allowed greater protein adsorption and enhanced mineralization when incubated in simulated body fluid. Moreover, our results indicated that human mesenchymal stem cells (hMSCs) seeded on these scaffolds were viable and could proliferate faster than in PCL scaffolds as confirmed by fluorescence and scanning electron microscopic observations. Further, osteogenic differentiation of hMSCs on nanoclay embedded scaffolds was demonstrated by an increase in alkaline phosphatase activity when compared to PCL scaffold without nanoclay. All of these results suggest the potential of PCL/NC scaffolds for bone tissue engineering.