Porous electrospun polycaprolactone fibers: Effect of process parameters

The effect of electrospinning process parameters (solution flow rate, applied voltage, spinning distance) on the size and surface morphology of porous electrospun poly(ε‐caprolactone) was investigated in this study. Response surface methodology was implemented for the design and conduction of electrospinning experiments. The feed solution was a 12.5% w/v poly(ε‐caprolactone) (PCL) solution in a binary solvent mixture of 90%v/v chloroform/dimethyl sulfoxide. Spinning distance of 10–25 cm, applied voltage of 10–25 kV and feed flow rate of 0.5–5 mL/h were the range of limiting values of the independent variables used for the development of a central composite design. Second‐order polynomial equations, correlating electrospinning process parameters to relative pore coverage, and fiber average diameter were developed and validated. An increase in any of the investigated parameters (solution flow rate, applied voltage, spinning distance) resulted in the increase of both, pore formation on electrospun fibers, and produced fiber average diameter. Under the experimental conditions investigated, the relative pore surface coverage was 15.8–31.9% and the average fiber diameter was in the range of 1.6–3.3 μm. Applied voltage was proven to be the parameter with the strongest impact on both, fiber diameter and surface morphology. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1878–1888     

Electrospinning P(LLA-CL) Nanofiber: A Tubular Scaffold Fabrication with Circumferential Alignment

In this paper a synthetic Poly(L-lactic-co-ϵ-caprolactone) [P(LLA-CL)] (75:25) copolymer has been fabricated into a nanofibrous structure by electrospinning. The polymer crystal structure has been investigated by DSC and x-ray diffraction method. During electrospinning at room temperature, a crystallization of LLA sequence in the P(LLA-CL) copolymer could not form, while a relatively regular arrangement of CL sequence was observed. In order to obtain a tubular scaffold, a rotating mandrel was designed to collect the fiber, so that the tubular scaffold can be retrieved from the mandrel with an inner diameter same as that of the outer diameter of the mandrel. An auxiliary electrode with a sharp edge and a negative charge was set under the mandrel to guide the fiber deposition on the mandrel. When the sharp edge bar was vertical to the rotating axle of the mandrel and just beneath the spinning nozzle, nanofibers with circumferential alignment were obtained. With this method it is possible to obtain a tubular scaffold with suitable fiber alignment for blood vessel tissue engineering.     

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Centrifugal spinning, a recently developed approach for ultra‐fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high‐voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle‐ and nozzle‐less centrifugal spinning systems. For nozzle‐less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle‐/nozzle‐less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1547–1559     

Electrospinning Process of Thermo-sensitive Poly(N-isopropylacrylamide) /poly (2-acrylamido-2-methylpropanesulfonic acid) Nanofibers

Poly (N-isopropylacrylamide)/poly (2-acrylamido-2-methylpropanesulfonic acid) (PNIPAAm/PAMPS) nanofibers was prepared using the electrospinning technique. The electrospinning process parameters such as solution concentration, voltage, receiver distance and flow rate were determined by the orthogonal experiments. The appropriate electrospinning parameters were 7.0% of solution concentration, 10.0 kV of voltage, 20 cm of distance and 3.1 μL·min^?1 of flow rate, respectively. The major factor affecting the nanofibers diameter was the solution concentration and the diameter increased with the solution concentration. The Fourier-transform infrared spectroscopy (FTIR) was conducted to characterize the structure of the components for electrospinning. Scanning electron microscopy (SEM) was taken to observe the morphology, and the contact angle (CA) measuring was carried out to determine the wettability of the nanofibers with temperatures. The results of SEM observation showed that the surfaces of nanofibers were smooth with uniform fibrous diameters and without the formation of beads. The CA detections showed that the electrospun PNIPAAm/PAMPS nanofibers exhibited thermo-sensitivity of hydrophilicity at 20°C and hydrophobicity at 40°C.     

Determining the effect of centrifugal and electrical forces on the jet behaviors,the nanofiber structure,and morphology

The increasing demand for nanofibers production has led to the rapid growth of the usage of electro‐centrifugal spinning (ECS) systems especially in recent years. Besides the rapid developments, fabrication of novel fibrous materials with novel techniques is still under investigation. Polyvinylepyrrolidone (PVP) is one of the multifunctional materials, which has attracted scientific interests to be employed in a variety of advanced applications. The main objective of the present study was therefore to explore the effects of essential parameters involved in fabrication of PVP nanofibers via an ECS system. The effects of rotational speed (197‐4051 r/min) and applied voltage (0‐14 kV) on the structural and morphological properties of nanofibers were also investigated. Analyses of the scanning electron microscope (SEM) images were performed with Digimizer and SPSS16.0 software to characterize the diameter distribution of the nanofibers. The degree of crystallinity was evaluated by the X‐ray diffraction method. In order to explain the unexpected results, further investigations were performed on the motion of the jet and flow rate. The results showed that instead of nanofibers, microparticles were formed at lower voltages and rotational speeds. The increase in the applied voltage resulted in a decrease in the minimum rotational speed that is required to form continuous fluid jet. The bending instabilities were changed from whipping to spiraling at the voltages above 10 kV. This resulted in the minimum fiber diameter at a voltage between 6 and 10 kV. Moreover, the applied voltage slightly affected the degree of crystallinity. No significant change was observed in the degree of crystallinity by varying the rotational speed.     

Nanofibrous Tubular Membrane for Blood Hemodialysis

As the most important components of a hemodialysis device, nanofibrous membranes enjoy high interconnected porosity and specific surface area as well as excellect permeability. In this study, a tubular nanofibrous membrane of polysulfone nanofibers was produced via electrospinning method to remove urea and creatinine from urine and blood serums of dialysis patients. Nanofibrous membranes were electrospun at a concentration of 11.5 wt% of polysulfone (PS) and dimethylformamide (DMF)/tetrahydrofuran (THF) with a ratio of 70/30. The effects of the rotational speed of collectors, electrospinning duration, and inner diameter of the tubular nanofibrous membrane on the urea and creatinine removal efficiency of the tubular membrane were investigated through the hemodialysis simulation experiments. It was found that the tubular membrane with an inner diameter of 3 mm elecrospun at shorter duration with lower collecting speed had the highest urea and creatinine removal efficiency. The hemodialysis simulation experiment showed that the urea and creatinine removal efficiency of the tubular membrane with a diameter of 3 mm were 90.4 and 100%, respectively. Also, three patients’ blood serums were tested with the nanofibrous membrane. The results showed that the creatinine and urea removal rates were 93.2 and 90.3%, respectively.     

Apoptosis Mechanism of Human Cholangiocarcinoma Cells Induced by Bile Extract from Crocodile

Animal bile is popularly used as a traditional medicine in China, and bile acids are their major bioactive constituents. In the present study, effects of bile extract from crocodile gallbladder on QBC939 cell growth, cell cycle, and apoptosis were investigated by MTT assay, inverted microscopy, fluorescence microscopy, transmission electron microscopy, scanning electron microscopy, PI single- and FITC/PI double-staining flow cytometry, and western blotting. Our data have revealed that bile extract inhibited cells growth significantly, and the cell cycle was arrested in G1 phase. Bile extract induced QBC939 cell apoptosis, which was associated with collapse of the mitochondrial membrane potential and increase of ROS. In bile extract-treated cells, it was observed that the expression of bcl-2 decreased and cytochrome c released to cytosol, but the expression of bax remained unchanged. The data indicated that mitochondrial pathway might play an important role in bile extract-induced apoptosis in QBC939 cells. These results provide significant insight into the anticarcinogenic action of bile extract on cholangiocarcinoma cells.     

Multiscale characterization of antimicrobial poly(vinyl butyral)/titania nanofibrous composites

Titania nanofillers were used to reinforce nanofibers in composite mats produced by electrospinning of poly(vinyl butyral) with two different concentrations of polymers. The titania nanoparticles and titania nanotubes were added into an acetic acid/ethanol solution in different contents of 3 and 1 wt%, respectively. The effect of the processing system on the morphology of the produced fibers was analyzed. The antimicrobial poly(vinyl butyral) composite fibers with titanium dioxide nanoparticles and titanium dioxide nanotubes were produced by single and multineedle electrospinning systems. This study reports fabrication of composite nanofibrous mats with significant mechanical and antimicrobial properties at a high production speed, which is promising for commercial applications (health care, photocatalysis, protective clothing, etc.). The reported result revealed an outstanding correlation between values of elastic modulus derived from nanoindentation and dynamic mechanical techniques. Copyright © 2017 John Wiley & Sons, Ltd.     

Electrospun polyethylene terephthalate (PET) nanofibrous conduit for biomedical application

Nanostructured biomaterials have great potential in the field of biomedical engineering. Efforts for treatment of cardiovascular diseases focused on introducing vascular substitutes that are nonthrombogenic and have long‐term patency, but still there is not any perfect replacement for clinical use. In this study, nanostructure tubes of a commonly known biocompatible polymer, polyethylene terephthalate (PET), were prepared via electrospinning process using small diameter mandrel as a collector with two different speeds. The nanofibers (NFs) morphologies' physical and mechanical properties were investigated according to scanning electron microscope (SEM), water contact angle (WCA), porosity measurement, differential scanning calorimetry (DSC), and tensile test. Finer NFs, more percentage of crystallinity, and superior mechanical properties were observed for samples prepared by higher speed mandrel. Since both samples stimulated platelet adhesion and activation, further surface modification with sodium nitrate as nitric oxide (NO) donor was done using two different approaches: dip‐coating and electrospraying. The modified NFs were evaluated via SEM, WCA, tensile test, platelets, and cell adhesion. The results showed more hydrophilicity, reduction in platelet adhesion, and improved blood compatibility for eNO‐HS (electrosprayed NO for higher collector speed) compared with other samples implying the promising potential of this fabrication and modification technique for improving PET‐based cardiovascular substitutes.     

一种实心针静电纺丝装置的场强模拟及优化

提出一种实心针静电纺丝方法, 采用实心针作为静电发射极, 并将其置于由绝缘材料制成的导液棒轴心, 导液棒处于储液盒底部的圆锥沉头通孔内部并可以做升降运动以控制供液量, 需要时还可以起到通流的作用, 有效地解决了多针头静电纺丝堵塞和无针头静电纺丝开放式供液的问题. 利用COMSOL有限元分析软件对影响场强大小及分布的各参数进行场强模拟, 研究增大场强并减小边缘效应的改进方法, 并采用研发的不完全齿轮横动机构纺丝头做往复横动进行纺丝实验, 验证了实心针静电纺丝装置有效降低了能耗和边缘效应, 避免了针头堵塞及溶剂挥发问题.     

采用静电纺丝/非溶剂致相分离制备聚丙烯腈多孔超细纤维的研究

以聚丙烯腈/二甲基亚砜/N,N'-二甲基甲酰胺三元体系为纺丝液、3℃水浴为接收介质,通过静电纺丝制备了具有纳米孔结构的静电纺聚丙烯腈多孔超细纤维.探讨了溶剂比例、接收介质、聚丙烯腈浓度、纺丝电压及接收距离等因素对纤维直径和表面孔隙率的影响.结果表明最佳制备条件为混合溶剂质量比1∶1、纺丝电压16 kV、聚丙烯腈浓度15 wt%、接收距离5 cm、纺丝速率0.7 mL/h、环境温度25℃、相对湿度40%～70%.在此条件下得到的聚丙烯腈多孔超细纤维直径在420～490 nm,平均直径468 nm,表面孔隙率3.4%,纤维内部形成大量孔径为8～30 nm的孔结构,且孔径分布均匀,孔形状相对一致.N2吸附脱附测试表明,聚丙烯腈多孔纤维的BET比表面积达43.86 m2/g,是相同直径无孔聚丙烯腈纤维比表面积理论值的6倍.通过研究聚丙烯腈/(二甲基亚砜+N,N'-二甲基甲酰胺)/水的三元相图,提出非溶剂致相分离是主要成孔机理.     

Persistent polarization in polymers. I. Relationship between the structure of polymers and their ability to become electrically polarized

The ability of various polymers to acquire persistent polarization (i.e., to become electrets) was investigated. Polarization was induced in the polymers by two methods: (a) by cooling under a voltage drop and (b) by cooling with flow under pressure. There was found to be an optimum temperature for electret formation by either method. This optimum temperature was roughly 37°C. above T_g when polarization was produced by application of a voltage drop and roughly 57°C. when polarization was produced by flow under pressure. Crystallinity and the nonhomogeneities present in blended polymers were harmful to electret formation, but a small critical amount of ionic impurity was helpful.     

Analysis of conjugated bile acids by on-line supercritical fluid chromatography/thermospra mass spectrometry

A rapid method was developed for the analysis or polar conjugated bile acids by combined packed column super-critical fluid chromatography/mass spectrometry. Direct coupling of the column to the mass spectrometer was effected with a modified thermospray interface operated in the filament-on mode. Maximum sensitivity for the bile acid conjugates was achieved by recording the negative ions generated in the ionization process. The effects of vaporizer and source temperatures, repeller voltage and discharge conditions on the bile acid response were investigated. The mass spectra obtained for the common glycine and taurine conjugates yielded only the [M – H]^? pseudo-molecular ions. In contrast with the taurine derivatives, the glycine forms produced a weak ion current and exhibited broad hands. The applicability of the technique is illustrated with a sample of human bile.     

Polysulfone nanofibers prepared by electrospinning and gas/jet-electrospinning

Polysulfone nanofibers were prepared by electrospinning. The electrospinning equipment was designed in a new way, wherein the spinneret was combined with a gas jet device. The intrinsic viscosity of the used polysulfone was 0.197 dL/g in dimethyl acetamide, which was also the solvent in electrospinning. The gas used in this gas jet/electrostatic spinning was nitrogen. The relationship between the process parameters and the average diameter of polysulfone nanofibers was investigated. The main process parameters studied in this work were the voltage, the flow rate of the spinning fluid, the distance between the spinneret and the nanofiber collector and the temperature in the spinning chamber. The other important factors determining the nanometer diameter were the spinning fluid properties including its viscosity, surface tension and electrical conductivity. The average diameter and the diameter distribution of electrospinning nanofibers were measured experimentally by using scanning electron microscopy. The diameter of polysulfone nanofibers prepared by the gas jet/electrostatic spinning was in the range 50–500 nm. It was found that the diameter of nanofibers mainly depended on high voltage, the gap between the spinneret and the collector and the concentration of polymer solutions. It is concluded that the gas-jet/electrospinning is a better method than the conventional electrospinning, in that it makes the nanofibers finer and more uniform and exhibits higher efficiency in the process of electrospinning. __________ Translated from Acta Polymerica Sinica, 2005, (5) (in Chinese)     

Turbulent drag reduction characteristics of poly(acrylamide-co-acrylic acid) in a rotating disk apparatus

The effects of experimental parameters such as temperature, polymer concentration, and rotational speed of the disk on drag reduction properties of water-soluble copolymer of poly(acrylamide-co-acrylic acid) in a turbulent flow were examined. Drag reduction (DR) efficacy up to 45% was found to be dependent on its medium temperature in a rotating disk apparatus. When the temperature was increased, the copolymer was found to be much susceptible to mechanical degradation, indicating that polymer chain scission becomes more severe at elevated temperatures. In addition, the optimum copolymer concentration for high DR efficacy was also observed.     

Optimization and characterization of electrospun chitosan/poly(vinyl alcohol) nanofibers as a phenol adsorbent via response surface methodology

Fabrication and characterization of chitosan/poly(vinyl alcohol) electrospun nanofibers for adsorption of phenol from water were investigated. The effects of voltage (15–30 kV), solution injection flow rate (0.5–1.5 ml/hr), distance of needle and collector (10–20 cm) and chitosan/poly(vinyl alcohol) ratio (25/75, 50/50, 75/25) were studied to obtain the optimum electrospinning conditions for the maximum adsorption capacity of phenol. Central composite design (CCD) was used to investigate and optimize the processing factors for production of chitosan/poly(vinyl alcohol) nanofibers from aqueous solutions. The nanofibers were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR). Uniform beadless nanofibers with the minimum diameters of 3–11 nm were obtained at chitosan/poly(vinyl alcohol) ratio of 50/50, voltage of 22.5 kV, distance of 15 cm and injection flow rate of 1.99 ml hr^?1. Fourier transform infrared spectrum of chitosan/poly(vinyl alcohol) exhibited the existence of relevant functional groups of both poly(vinyl alcohol) and chitosan in the blends. Results of CCD show that among all processing factors, rate of electrospinning will highly affect the nanofiber adsorption. The response surface quadratic order model presented correlation coefficient explaining 69.5% of the variability in the adsorption. Copyright © 2017 John Wiley & Sons, Ltd.     

PLGA/明胶共混体系的静电纺丝研究

采用静电纺丝技术制备了聚乳酸乙醇酸(PLGA)/明胶(Gt)的复合超细纤维, 考察了溶液浓度、电压及流速对纤维形貌的影响. 研究了不同明胶比例的纤维膜的微观形貌和干湿态的力学性能. 结果表明, 在溶液浓度0.12 g/mL, 电压7.5 kV, 流速0.8 mL/h条件下, 所得PLGA/Gt复合纤维直径较小, 粗细较均匀且缺陷少. 含有明胶的复合纤维直径远小于PLGA单纺纤维直径, 明胶的加入降低了膜的拉伸强度和断裂伸长率, 提高了膜的亲水性. 经PBS浸泡后, 复合膜的弹性得到加强. 明胶质量分数为5%和10%时, 纤维直径分布较窄, 当明胶的质量分数增加至15%时, 纤维的直径分布变宽.     

Influence of flow patterns on chromatographic efficiency in centrifugal partition chromatography

Visualization of flow patterns in centrifugal partition chromatography (CPC) was performed with an asynchronous camera and a stroboscope triggered by the CPC rotor, allowing a channel to be selected and observed regardless of rotational speed. Three main types of flow states were noted as a function of rotational speed and flow-rate: jets stuck along channel walls, broken jets and atomization. Our observations emphasize the importance of Coriolis force on flow shape. Chromatographic efficiency was related to the dispersion of the mobile phase in the stationary phase.     

毛细管电泳-电化学发光法检测泛昔洛韦

建立了毛细管电泳-电化学发光(CE-ECL)法检测泛昔洛韦的新方法。考察了检测电位、运行高压、进样电压与时间、检测池中磷酸盐的pH值、运行缓冲溶液的pH值及浓度等测试条件对电化学发光强度的影响。在最优化的实验条件下,泛昔洛韦在5.0×10-6～2.5×10-4mol/L浓度范围内与电化学发光强度有良好的线性关系,相关系数为0.9973,检出限为3.5×10-6mol/L。该法灵敏度高,选择性好,可应用于泛昔洛韦原料药及制剂的质量控制。初步探讨了CE-ELC检测泛昔洛韦的机理。     

Large‐scale aligned fiber mats prepared by salt‐induced pulse electrospinning

In this article, a new large‐scale aligned fiber mats formation method called salt‐induced pulse electrospinning was developed. By electrospinning salted solution in a humid environment, traditional continuous electrospinning changed into pulse electrospinning and aligned fibers were thus formed. The possible mechanisms for the occurrence of salt‐induced pulse electrospinning and the formation of fiber alignment were studied. The continuous electrospinning changing into the pulse electrospinning was due to the change of viscosity and conductivity of salted polymer solution in a wet electrospinning condition. Fishing net‐shaped whipping region of the electrospinning jet during pulse electrospinning process was considered as the key factor for the formation of fiber alignment. The mechanical properties of the aligned fiber mat increased significantly compared with that of the random fiber mat. This aligned fiber preparation method only requires a very low rotating drum speed as the receiver and can produce large‐scale aligned fiber mats for many applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012