Morphological and surface properties of electrospun chitosan nanofibers

Nonwoven fiber mats of chitosan with potential applications in air and water filtration were successfully made by electrospinning of chitosan and poly(ethyleneoxide) (PEO) blend solutions. Electrospinning of pure chitosan was hindered by its limited solubility in aqueous acids and high degree of inter- and intrachain hydrogen bonding. Nanometer-sized fibers with fiber diameter as low as 80 +/- 35 nm without bead defects were made by electrospinning high molecular weight chitosan/PEO (95:5) blends. Fiber formation was characterized by fiber shape and size and was found to be strongly governed by the polymer molecular weight, blend ratios, polymer concentration, choice of solvent, and degree of deacetylation of chitosan. Weight fractions of polymers in the electrospun nonwoven fibers mats were determined by thermal gravimetric analysis and were similar to ratio of polymers in the blend solution. Surface properties of fiber mats were determined by measuring the binding efficiency of toxic heavy metal ions like chromium, and they were found to be related with fiber composition and structure.     

One-step electrospinning of cross-linked chitosan fibers

Chitin is a nitrogen-rich polysaccharide that is abundant in crustaceans, mollusks, insects, and fungi and is the second most abundant organic material found in nature next to cellulose. Chitosan, the N-deacetylated derivative of chitin, is environmentally friendly, nontoxic, biodegradable, and antibacterial. Fibrous mats are typically used in industries for filter media, catalysis, and sensors. Decreasing fiber diameters within these mats causes many beneficial effects such as increased specific surface area to volume ratios. When the intrinsically beneficial effects of chitosan are combined with the enhanced properties of nanofibrous mats, applications arise in a wide range of fields, including medical, packaging, agricultural, and automotive. This is particularly important as innovative technologies that focus around bio-based materials are currently of high urgency, as they can decrease dependencies on fossil fuels. We have demonstrated that Schiff base cross-linked chitosan fibrous mats can be produced utilizing a one-step electrospinning process that is 25 times faster and, therefore, more economical than a previously reported two-step vapor-cross-linking method. These fibrous mats are insoluble in acidic, basic, and aqueous solutions for 72 h. Additionally, this improved production method results in a decreased average fiber diameter, which measures 128 +/- 40 nm. Chemical and structural analyses were conducted utilizing Fourier transform infrared spectroscopy, solubility studies, and scanning electron microscopy.     

Fabrication and characterization of electrospun chitosan nanofibers formed via templating with polyethylene oxide

Chitosan is an abundantly common, naturally occurring, polysaccharide biopolymer. Its biocompatible, biodegradable, and antimicrobial properties have led to significant research toward biological applications such as drug delivery, artificial tissue scaffolds for functional tissue engineering, and wound-healing dressings. For applications such as tissue scaffolding, formation of highly porous mats of nanometer-sized fibers, such as those fabricated via electrospinning, may be quite important. Previously, strong acidic solvents and blending with synthetic polymers have been used to achieve electrospun nanofibers containing chitosan. As an alternative approach, in this work, polyethylene oxide (PEO) has been used as a template to fabricate chitosan nanofibers by electrospinning in a core-sheath geometry, with the PEO sheath serving as a template for the chitosan core. Solutions of 3 wt % chitosan (in acetic acid) and 4 wt % PEO (in water) were found to have matching rheological properties that enabled efficient core-sheath fiber formation. After removing the PEO sheath by washing with deionized water, chitosan nanofibers were obtained. Electron microscopy confirmed nanofibers of approximately 250 nm diameter with a clear core-sheath geometry before sheath removal, and chitosan nanofibers of approximately 100 nm diameter after washing. The resultant fibers were characterized with IR spectroscopy and X-ray diffraction, and the mechanical and electrical properties were evaluated.     

Morphology and structure of electrospun mats from regenerated silk fibroin aqueous solutions with adjusting pH

In this paper, regenerated silk fibroin (SF) aqueous solutions were adjusted to a pH of 6.9 by mimicing the condition in the posterior division of silkworm's gland and rheological behavior of solutions was investigated. The electrospinning technique was used to prepare fibers, and non-woven mats of regenerated B. mori silk fibroin were successfully obtained. The effects of electrospinning parameters on the morphology and diameter of regenerated silk fibers were investigated by orthogonal design. Statistical analysis showed that voltage, the concentration of regenerated SF solutions and the distance between tip and collection plate were the most dominant parameters to fiber morphology, diameter and diameter distribution, respectively. An optimal electrospinning condition was obtained in producing uniform cylindrical fibers with an average diameter of 1300nm. It was as follows: the concentration 30%, voltage 40kV, distance 20cm. The structure of electrospun mats was characterized by Raman spectroscopy (RS), wide-angle X-ray diffraction (WAXD) and modulated differential scanning calorimetry (MDSC). It was found that electrospun mats were predominantly random coil/silk I structure, and the transition to silk II (beta-sheet) rich structure should be further explored.     

Effect of Process Parameters on the Microstructural Characteristics of Electrospun Poly(Vinyl Alcohol) Fiber Mats

Fiber mats with average fiber diameter ranging between 80 and 250 nm of polyvinyl alcohol (PVA)/water solution having a concentration of 4 wt.% have been prepared by electrospinning method. The influence of applied voltage, flow rate, and needle-to-collector distance on the fiber morphology and diameters has been studied. Scanning electron microscopy and atomic force microscopy are used to characterize the fibers. It has been observed that bead-free fibers of 4 wt.% PVA can be obtained at lower voltages (9 kV). Also, density and the deposition area of the fiber mats showed a clear dependence on the applied voltage, flow rate, and collector distance.     

Electrospinning of poly(vinyl alcohol)-water-soluble quaternized chitosan derivative blend

Defect free mats containing a cationic polysaccharide, chitosan derivative such as N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC), have been prepared using electrospinning of an aqueous solution of poly(vinyl alcohol) (PVA)-HTCC blends. HTCC, a water-soluble derivative of chitosan, was synthesized via the reaction between glycidyl-trimethylammonium chloride and chitosan. Solutions of PVA-HTCC Blends were electrospun. The morphology, diameter and structure of the produced electrospun nanofibres were examined by scanning electron microscopy (SEM). The average fibre diameter was in the range of 200-600 nm. SEM images showed that the morphology and diameter of the nanofibres were mainly affected by weight ratio of the blend and applied voltage. The results revealed that increasing HTCC content in the blends decreases the average fibre diameter. These observations were discussed on the basis of shear viscosities and conductivities of the spinning solutions. Microbiological assessment showed that the PVA-HTCC mats have a good antibacterial activity against Gram-positive bacteria, Staphylococcus aureus, and Gram-negative bacteria, Escherichia coli.     

Electrospun water-soluble carboxyethyl chitosan/poly(vinyl alcohol) nanofibrous membrane as potential wound dressing for skin regeneration

Biocompatible carboxyethyl chitosan/poly(vinyl alcohol) (CECS/PVA) nanofibers were successfully prepared by electrospinning of aqueous CECS/PVA solution. The composite nanofibrous membranes were subjected to detailed analysis by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). SEM images showed that the morphology and diameter of the nanofibers were mainly affected by the weight ratio of CECS/PVA. XRD and DSC demonstrated that there was strong intermolecular hydrogen bonding between the molecules of CECS and PVA. The crystalline microstructure of the electrospun fibers was not well developed. The potential use of the CECS/PVA electrospun fiber mats as scaffolding materials for skin regeneration was evaluated in vitro using mouse fibroblasts (L929) as reference cell lines. Indirect cytotoxicity assessment of the fiber mats indicated that the CECS/PVA electrospun mat was nontoxic to the L929 cell. Cell culture results showed that fibrous mats were good in promoting the cell attachment and proliferation. This novel electrospun matrix would be used as potential wound dressing for skin regeneration.     

Cross-linking chitosan nanofibers

In the present study, we have electrospun various grades of chitosan and cross-linked them using a novel method involving glutaraldehyde (GA) vapor, utilizing a Schiff base imine functionality. Chemical, structural, and mechanical analyses have been conducted by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Kawabata microtensile testing, respectively. Additionally, the solubilities of the as-spun and cross-linked chitosan mats have been evaluated;solubility was greatly improved after cross-linking. SEM images displayed evidence that unfiltered low, medium, and high molecular weight chitosans, as well as practical-grade chitosan, can be electrospun into nanofibrous mats. The as-spun medium molecular weight chitosan nanofibers have a Young's modulus of 154.9 +/- 40.0 MPa and display a pseudo-yield point that arose due to the transition from the pulling of a fibrous mat with high cohesive strength to the sliding and elongation of fibers. As-spun mats were highly soluble in acidic and aqueous solutions. After cross-linking, the medium molecular weight fibers increased in diameter by an average of 161 nm, have a decreased Young's modulus of 150.8 +/- 43.6 MPa, and were insoluble in basic, acidic, and aqueous solutions. Though the extent to which GA penetrates into the chitosan fibers is currently unknown, it is evident that the cross-linking resulted in increased brittleness, a color change, and the restriction of fiber sliding that resulted in the loss of a pseudo-yield point.     

Correlation of chitosan's rheological properties and its ability to electrospin

Chitosan-based, defect-free nanofibers with average diameters ranging from 62 +/- 9 nm to 129 +/- 16 nm were fabricated via electrospinning blended solutions of chitosan and polyethylene oxide (PEO). Several solution parameters such as acetic acid concentration, polymer concentration, and polymer molecular weight were investigated to optimize fiber consistency and diameter. These parameters were evaluated using the rheological properties of the solutions as well as images produced by scanning electron microscopy (SEM) of the electrospun nanofibers. Generally, SEM imaging demonstrated that as total polymer concentration (chitosan + PEO) increased, the number of beads decreased, and as chitosan concentration increased, fiber diameter decreased. Chitosan-PEO solutions phase separate over time; as a result, blended solutions were able to be electrospun with the weakest electric field and the least amount of complications when solutions were electrospun within 24 h of initially being blended. The addition of NaCl stabilized these solutions and increased the time the blended solutions could be stored before electrospinning. Pure chitosan nanofibers with high degrees of deacetylation (about 80%) were unable to be produced. When attempting to electrospin highly deacetylated chitosan from aqueous acetic acid at concentrations above the entanglement concentration, the electric field was insufficient to overcome the combined effect of the surface tension and viscosity of the solution. Therefore, the degree of deacetylation is an extremely important parameter to consider when attempting to electrospin chitosan.     

Electrospun polyethylene oxide/cellulose nanocrystal composite nanofibrous mats with homogeneous and heterogeneous microstructures

An electrospinning process was successfully used to fabricate polyethylene oxide/cellulose nanocrystal (PEO/CNC) composite nanofibrous mats. Transition of homogeneous to heterogeneous microstructures was achieved by tailoring the concentration of PEO/CNC mixture in the solution from 5 to 7 wt %. Morphology investigation of the obtained nanofibers demonstrated that rod-shaped CNCs were well-dispersed in the as-spun nanofibers and highly aligned along the nanofiber long-axis. PEO/CNC nanofibers became more uniform and smaller in diameter with increased CNC-loading level. The heterogeneous composite mats were composed of rigid-flexible bimodal nanofibers. Results of structure characterization indicated that the incorporated CNCs interacted strongly with the PEO matrix through hydrogen bonding. Mechanical properties of both types of mats were effectively improved by using CNCs, with heterogeneous mats being stronger than their homogeneous counterparts for all compositions (0-20 wt % CNC contents). When a smaller diameter needle was used to form homogeneous mats, enhanced thermal and mechanical properties were obtained.     

LBL fabricated biopolymer-layered silicate based nanofibrous mats and their cell compatibility studies

N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) was synthesized from chitosan (CS). Organic rectorite (OREC) added into cellulose acetate (CA) was used to fabricate electrospun nanofibrous mats with improved thermal properties, as a result of depositing multilayers of the positively charged HTCC-OREC composites and the negatively charged sodium alginate (ALG) via layer-by-layer (LBL) technique. The morphology was affected by the number of deposition bilayers and the component of the outmost layer. Observed from the field emission scanning electron microscopy (FE-SEM) images, the LBL structured nanofibrous mats had much larger fiber sizes than CA-OREC nanofibrous mats. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results further confirmed that HTCC-OREC was assembled on nanofibrous mats. Additionally, cell experiments and MTT results demonstrated that OREC had little effect on the cytotoxicity of LBL template, but obviously affected both the cytotoxicity and the cell compatibility of LBL structured mats when OREC was in the deposition films.     

PHBV‐TiO2 mats prepared by electrospinning technique: Physico‐chemical properties and cytocompatibility

One of the most important challenges in tissue engineering research is the development of biomimetic materials. In this present study, we have investigated the effect of the titanium dioxide (TiO₂) nanoparticles on the properties of electrospun mats of poly (hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), to be used as scaffold. The morphology of electrospun fibers was observed by scanning electron microscopy (SEM). Both pure PHBV and nanocomposites fibers were smooth and uniform. However, there was an increase in fiber diameter with the increase of TiO₂ concentration. Thermal properties of PHBV and nanocomposite mats were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis showed that the crystallization temperature for PHBV shifts to higher temperature in the presence of the nanoparticles, indicating that TiO₂ nanoparticles change the process of crystallization of PHBV due to heterogeneous nucleation effect. TGA showed that in the presence of the nanoparticles, the curves are shifted to lower temperatures indicating a decreasing in thermal stability of nanocomposites compared to pure PHBV. To produce scaffolds for tissue engineering, it is important to evaluate the biocompatibility of the material. Cytotoxicity assay showed that TiO₂ nanoparticles were not cytotoxic for cells at the concentration used to synthesize the mats. The proliferation of cells on the mats was evaluated by the MTT assay. Results showed that the nanocomposite samples increased cell proliferation compared to the pure PHBV. These results indicate that continuous electrospun fibrous scaffolds may be a good substrate for tissue regeneration.     

Electrospinning: A fascinating fiber fabrication technique

With the emergence of nanotechnology, researchers become more interested in studying the unique properties of nanoscale materials. Electrospinning, an electrostatic fiber fabrication technique has evinced more interest and attention in recent years due to its versatility and potential for applications in diverse fields. The notable applications include in tissue engineering, biosensors, filtration, wound dressings, drug delivery, and enzyme immobilization. The nanoscale fibers are generated by the application of strong electric field on polymer solution or melt. The non-wovens nanofibrous mats produced by this technique mimics extracellular matrix components much closely as compared to the conventional techniques. The sub-micron range spun fibers produced by this process, offer various advantages like high surface area to volume ratio, tunable porosity and the ability to manipulate nanofiber composition in order to get desired properties and function. Over the years, more than 200 polymers have been electropun for various applications and the number is still increasing gradually with time. With these in perspectives, we aim to present in this review, an overview of the electrospinning technique with its promising advantages and potential applications. We have discussed the electrospinning theory, spinnable polymers, parameters (solution and processing), which significantly affect the fiber morphology, solvent properties and melt electrospinning (alternative to solution electrospinning). Finally, we have focused on varied applications of electrospun fibers in different fields and concluded with the future prospects of this efficient technology.     

Core-shell structured PEO-chitosan nanofibers by coaxial electrospinning

Core-shell structured PEO-chitosan nanofibers have been produced using a coaxial electrospinning setup. PEO and chitosan solutions, both in an aqueous acetic acid solvent, were used as the inner (core) and outer (shell) layer, respectively. Uniform-sized defect-free nanofibers of 150-190 nm diameter were produced. In addition, hollow nanofibers could be obtained subsequent to PEO washing of the membranes. The core-shell nanostructure and existence of chitosan on the shell layer were confirmed by TEM images obtained before and after washing the PEO content with water. The presence of chitosan on the surface of the composite nanofibers was further supported by XPS studies. The chitosan and PEO compositions in the nanofibrous mats were determined by TGA analysis, which were similar to their ratio in the feed solutions. The local compositional homogeneity of the membranes and the efficiency of the washing step to remove PEO were also verified by FTIR. In addition, DSC and XRD were used to characterize the crystalline structure and morphology of the co-electrospun nonwoven mats. The prepared coaxial nanofibers (hollow and solid) have several potential applications due to the presence of chitosan on their outer surfaces.     

Electrospun nano-fiber mats containing cationic cellulose derivatives and poly (vinyl alcohol) with antibacterial activity

Nano-fibrous mats have been successfully prepared by electrospinning of the blend solutions of cationic cellulose derivatives (PQ-4) and polyvinyl alcohol (PVA). Effects of the blending ratio and applied voltage on the morphology and diameter of the electrospun nano-fibers were investigated. The average diameter of the PQ-4/PVA blend fibers was in the range of 150–250 nm. The electrospinning process became instable and the fiber diameter distribution broadened with increasing PQ-4 content and applied voltage. The antibacterial activity of electrospun PQ-4/PVA blend mats against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus indicated potential for biomedical use.     

静电纺丝的主要参数对PLGA纤维支架形貌和纤维直径的影响

EST(expressed sequence tags,EST)是一段长约150～500bp基因表达的外源序列片段,是由大规模随机挑取的cDNA克隆测序得到的组织或细胞基因组的表达序列标签。一个EST代表生物某一时期的某种组织或细胞的一个表达基因。主要综述了EST技术的原理方法,哺乳动物早期胚胎研究的理论基础以及EST技术在早期胚胎研究方面的应用,并讨论了利用EST进行研究分析的发展趋势。     

静电纺丝的主要参数对ＰＬＧＡ纤维支架形貌和纤维直径的影响

目的以聚乳酸-羟基乙酸共聚物(PLGA)为材料,采用静电纺丝方法制备纤维支架,考察制备参数对纤维支架结构及纤维直径的影响规律。方法以四氢呋喃(THF)和N,N-二甲基甲酰胺(DMF)的混合液为溶剂,调节PLGA溶液浓度、流量及电场强度分别制备了具有不同表面形貌的纤维支架。通过扫描电镜(SEM)观察了纺丝溶液的浓度、流量及电场强度对纤维形貌和直径的影响。同时在制备的PLGA纤维支架上接种了人的真皮成纤维细胞,并对细胞在PLGA支架上的黏附和增殖情况进行了研究,从而来评价支架材料的细胞相容性。结论结果表明,随着纺丝溶液浓度的增加,纤维直径逐渐增大,纤维直径的分布也随之增大。随着流量的增加,纤维直径略有增大。随着电场强度的增大,纤维直径没有明显的变化。但是电压和浓度的增大有助于减少珠丝的产生。体外细胞培养实验证明,制备的PLGA纤维支架能支持细胞正常的黏附和增殖活动。     

Preparation of electrospun polycaprolactone nanofiber mats loaded with microalgal extracts

Sustainable, ecological, and biocompatible materials are emerging for the development of novel components for tissue engineering. Microalgae being one of the unique organisms on Earth to provide various novel compounds with certain bioactivities are also a good source for the development of novel tissue scaffold materials. In this study, electrospinning technique was utilized to fabricate nanofibers from polycaprolactone loaded with microalgal extracts obtained from Haematococcus pluvialis (vegetative and carotenoid producing form) and Chlorella vulgaris. The FTIR results showed that, blending microalgae with polycaprolactone give unique bands rooted from microalgae and polycaprolactone structure. The samples were not diversified from each other, however stable bands were observed. SEM analysis revealed a uniform fiber fabrication with an average diameter of 810 ± 55 nm independent from microalgal extracts. MTT assay was done on HUVEC cell lines and results showed that nanofiber mats helped cell proliferation with extended time. Biodegradation resulted with mineral accumulation on the surface of same samples however the fiber degradation was uniform. With slow but stable biodegradation characteristics, microalgal extract loaded nanofiber mats holds great potential to be novel tissue scaffold material.     

Electrospun nano-fibre mats with antibacterial properties from quaternised chitosan and poly(vinyl alcohol)

Nano-fibres containing quaternised chitosan (QCh) have been successfully prepared by electrospinning of QCh solutions mixed with poly(vinyl alcohol) (PVA). The average fibre diameter is in the range of 60-200 nm. UV irradiation of the composite electrospun nano-fibrous mats containing triethylene glycol diacrylate as cross-linking agent has resulted in stabilising of the nano-fibres against disintegration in water or water vapours. Microbiological screening has demonstrated the antibacterial activity of the photo-cross-linked electrospun mats against Staphylococcus aureus and Escherichia coli. The obtained nano-fibrous electrospun mats are promising for wound-healing applications.     

Study on cast membranes and electrospun nanofibers made from keratin/fibroin blends

Keratin regenerated from wool and fibroin regenerated from silk were mixed in different proportions using formic acid as the common solvent. Both solutions were cast to obtain films and electrospun to produce nanofibers. Scanning electron microscopy investigation showed that, for all electrospun blends (except for 100% keratin where bead defects are present), the fiber diameter of the mats ranged from 900 (pure fibroin) to 160 nm (pure keratin). FTIR and DSC analysis showed that the secondary structure of the proteins was influenced by the blend ratios and the process used (casting or electrospinning). Prevalence of beta-sheet supramolecular structures was observed in the films, while proteins assembled in alpha-helix/random coil structures were observed in nanofibers. Higher solution viscosity, thinner filaments, and differences in the thermal and structural properties were observed for the 50/50 blend because of the enhanced interactions between the proteins.