The effect of temperature and humidity on electrospinning

Electrospinning is a process that generates nanofibres. Temperature and humidity affect this process. In this article the influence of humidity and temperature on the formation and the properties of nanofibres are studied using cellulose acetate (CA) and poly(vinylpyrrolidone) (PVP) as target materials. The experiments indicate that two major parameters are dependent of temperature and have their influence on the average fibre diameter. A first parameter is the solvent evaporation rate that increases with increasing temperature. The second parameter is the viscosity of the polymer solution that decreases with increasing temperature. The trend in variation of the average nanofibre diameter as a function of humidity is different for CA and PVP, which can be explained by variations in chemical and molecular interaction and its influence on the solvent evaporation rate. As the humidity increases, the average fibre diameter of the CA nanofibres increases, whilst for PVP the average diameter decreases. The average diameter of nanofibres made by electrospinning change significantly through variation of temperature and humidity.     

Solvent control of cellulose acetate nanofibre felt structure produced by electrospinning

Non-woven structures of cellulose acetate (CA) fibres of 90 nm–5 μm in diameter (spinning parameters 90 nm beaded fibres: 12% CA in EtOH-DMSO 1/1, 22 kV, 30 cm, 0.5 mL/h; maximum 5 μm diameter fused fibres spun with 14% CA in Ac-BenzOH 2/1, 22 kV, 24 cm, 13 mL/h) were produced by electrospinning. On the basis of Hansen solubility theory, composition of binary solvent mixtures (ketones—acetone, methyl ethyl ketone (MEK), and alcohols—benzyl alcohol, propylene glycol and dimethylsulphoxide) was optimized with respect to control of fibre felt morphology. Fibre networks of high packing density were obtained with binary low-volatile alcohols/MEK solvent mixtures, a decreased spinning distance and an increased feed rate. Substituting MEK by acetone in the solvent mixture resulted in the formation of nanofibre felt with a low degree of fibre cross-links. Thus, solvent control is a key aspect for control of electrospun fibre felt structures, which may serve as scaffolds for tissue engineering.     

Processing and properties of poly(ε-caprolactone)/carbon nanofibre composite mats and films obtained by electrospinning and solvent casting

Composite materials based on poly(ε-caprolactone) (PCL) and carbon nanofibres (CNFs) were processed by solvent casting and electrospinning. The main objective was to investigate the effects of the CNFs on the microstructural, thermal and mechanical properties of the PCL matrix composites processed by two different routes. The hybrid materials obtained with different CNF content (1, 3 and 7 wt%) were analysed by electron microscopy (FESEM), differential scanning calorimeter (DSC), thermogravimetry (TGA) and mechanical testing. The composite films showed a good dispersion in the PCL matrix while electrospun samples were consisted of homogeneous and uniform fibres up to 3 wt% CNFs with average fibre diameter ranged between 0.5 and 1 μm. Composite films and mats revealed an increased crystallization temperature with respect to the neat PCL matrix. Mechanical properties of solvent cast films and electrospun mats were assessed by uniaxial tensile tests. A stiffness increase was achieved in PCL films depending on the CNF content, while mechanical properties of mats were only slightly affected by CNF introduction.     

Effect of the relative humidity on the fibre morphology of polyamide 4.6 and polyamide 6.9 nanofibres

To obtain uniform and reproducible nanofibres, it is important to understand the effect of the different electrospinning parameters on the nanofibre morphology. Even though a lot of literature is available on the electrospinning of nanofibres, only minor research has been performed on the effect of the relative humidity (RH). This paper investigates the influence of this parameter on the electrospinning process and fibre morphology of the hydrophilic polyamide 4.6 and the less hydrophilic polyamide 6.9. First, the electrospinning process and deposition area of the nanofibres is examined at 10, 50 and 70 % RH. Subsequently, the effect of the polyamide concentration and solvent ratio on the fibre morphology is investigated using scanning electron microscopy and differential scanning calorimetry. It was found that the nanofibre diameter decreased with increasing RH. This resulted in less stable crystals for polyamide 4.6 while electrospinning of polyamide 6.9 at higher RH led to slightly more stable crystals. In conclusion, the water affinity of a polymer is an important factor in predicting the nanofibre morphology at different humidities.     

Melt-electrospinning of polypropylene with conductive additives

In this paper, the feasibility of fabricating polypropylene (PP) nanofibres was investigated using conductive additives such as sodium oleate (SO) and sodium chloride (NaCl) during melt-electrospinning. PP of high melt flow index (MFI = 2000) was used with varying amounts of additives. The effects of amount of additives on the fibre diameter and morphology were investigated. The lowest fibre diameters of 0.371 ± 0.106 and 0.310 ± 0.102 μm were achieved with 7 % SO and 5 % NaCl, respectively. The fabrication of nanofibres was attributed to the increase in the electrical conductivity with the introduction of the additives. The increase in the electrical conductivity was greater in the case of NaCl, due to the smaller ionic size of NaCl. Differential scanning calorimetry results showed complex melting behaviour during the heating cycles for the fibres containing SO; and double melting peaks during the second heating cycle for the fibres containing NaCl. X-ray diffraction studies showed the fibres fabricated with the additives contained lower degrees of crystallinity compared to the as-spun fibre and the crystallinity was increased after annealing. The fibres fabricated with the additives contained α-form crystals only which did not change after annealing. The fibres fabricated from pure polymer and with the additives were hydrophobic in nature. The hydrophobicity was marginally decreased with the addition of SO and NaCl.     

Functional polyaniline nanofibre mats for human adipose-derived stem cell proliferation and adhesion

Conductive polymer poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) and polyaniline (PANI) were blended with a biodegradable, biocompatible polymer, poly(l-lactic acid) and were electrospun into nanofibres to investigate their potential application as a scaffold for human adipose-derived stem cells (hASCs). These polymers, in both conductive and non-conductive form, were electrospun with average fibre diameters of less than 400 nm. Novel nanoindentation results obtained on the individual nanofibres revealed that the elastic moduli of the nanofibres are much higher at the surface (4–10 GPa, h_max <75 nm) than in the inner fibre core (2–4 GPa, h_max >75 nm). The composite nanofibres showed great promise as a scaffold for hASCs as they supported the cell adhesion and proliferation. After 1 week of cell culture hASCs were well spread on the substrates with abundant focal adhesions. The electrospun mats provide the cells with comparably stiff, sub-micron sized fibres as anchoring points on a substrate of high porosity. The conductive nature of these composite nanofibres offers exciting opportunities for electrical stimulation of the cells.     

The effects of cellulose nanowhiskers on electrospun poly (lactic acid) nanofibres

The effects of cellulose nanowhiskers on the microstructure and thermal behaviour of electrospun poly (lactic acid) (PLA) nanofibres have been investigated in this study. The PLA/cellulose nanowhiskers composite nanofibres are successfully produced by electrospinning the mixtures of cellulose whiskers with PLA solution. The diameters of PLA and its composites are around 300 nm. The scanning electron micrographs show that the cellulose nanowhiskers do not protrude out of the outer surfaces of PLA nanofibres. The existence of cellulose nanowhiskers in the electrospun PLA matrix nanofibres, and the microstructural evolution are investigated by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) analysis shows the formation trend of PLA α crystal with the addition of cellulose nanowhiskers. The electrospun PLA and PLA/cellulose nanowhiskers composites reveal very low crystallinity due to the rapid solvent evaporation and relatively slow crystallisation kinetics character of PLA. The electrospun nanofibres show particularly different thermal behaviour from that of the solution cast films. The nanofibres of pure PLA and PLA/cellulose nanowhiskers experience two consecutively overlapping crystallisation processes. The cellulose nanowhiskers act as heterogeneous sites for nucleation of PLA by decreasing the cold crystallisation onset temperature. The incorporation of cellulose nanowhiskers into PLA nanofibres is expected to improve mechanical properties and bring new functionalities to the electrospun matrix nanofibres.     

Polyurethane foam containing microencapsulated phase-change materials with styrene–divinybenzene co-polymer shells

Polyurethane (PU) foam containing phase change materials is a kind of new heat-insulating material which can store and release heat energy. The microencapsulated n-octadecane (MicroPCMs) with a styrene (St)–divinybenzene (DVB) co-polymer shell was synthesized by means of suspension-like polymerization. The surface morphology, diameter, enthalpy, and thermal stability were investigated by using scanning electronic microscope (SEM), differential scanning calorimeter (DSC), and TGA. The average diameter of the microcapsules is about 80 μm. The enthalpy of the microcapsule is about 126 J/g. PU foams containing MicroPCMs were fabricated by adding the MicroPCMs in reactants. MicroPCMs are evenly inserted inside the foam and the enthalpy of the foam rises with the increase of the content of microcapsules. The enthalpy is about 24 J/g for the foam containing 26.8 wt% MicroPCMs.     

Statistical optimization of the electrospinning process for chitosan/polylactide nanofabrication using response surface methodology

In this study, chitosan/polylactide (CP) blend solutions in trifluoroacetic acid as a co-solvent with different blend ratio were electrospun. Effects of different CP ratio and process parameters on the diameter of electrospun nanofibers were experimentally investigated. The fiber morphology and the distribution of fiber diameter were investigated by scanning electron microscopy. Response surface methodology (RSM) was used to define and evaluate a quantitative relationship between electrospinning parameters, average fiber diameters and its distribution for each chitosan–polylactide ratio. Applied voltage and polymer solution extrusion rate are the process variables which control the fiber diameter at similar spinning distances (15 cm). Fiber diameter was correlated to these variables by using a second-order polynomial function. The fibers were of diameter ranging from 94 to 389 nm. The predicted fiber diameters were in good agreement with the experimental results. Contour plots were obtained to identify the processing variables suitable for producing nanofibers. It was concluded that ratio of polylactide and chitosan in the blend polymer played an important role to the diameter of fibers and standard deviation of fiber diameter. The processing factors were found statistically significant in the production of nanofibers.     

Investigation of fibroblast and keratinocyte cell-scaffold interactions using a novel 3D cell culture system

In this study we investigated the influence of fibre diameter and interfibre space in 3D scaffolds on cellular behaviour of human dermal fibroblasts and a human keratinocyte cell line (HaCaT cell). Electrospun aligned poly L-lactic acid fibres (2–10 μ m) were bound to form fibres with a broad range of diameters (2–120 μ m) and then constructed in a specifically designed 3D cell culture system. Human dermal fibroblasts were introduced to one end of the free-standing fibres using a fibrin clot and encouraged to ‘walk the plank’. Under these conditions it was observed that a minimum fibre diameter of 10 μ m for fibroblast adhesion and migration arose. A thin layer of electrospun viscose rayon scaffold fibres (diameter 30–50 μ m, pore size 50–300 μ m) was also constructed in the 3D cell culture system. After introduction to the scaffold using cells contained within a fibrin clot, fibroblasts were observed to stratify and also elongate between fibres in order to occupy voids. An interfibre span of up to 200 μ m was possible by a single fibroblast, but more commonly void distances were spanned by cellular multilayering. In contrast, HaCaT keratinocytes cultured under identical conditions using viscose rayon scaffolds occupied very much smaller void distances of 50–80 μ m predominantly by stratification.     

Structure and properties of electrospun PLLA single nanofibres

An electrospinning method was used to spin semi-crystalline poly(L-lactide) (PLLA) nanofibres. Processing parameter effects on the internal molecular structure of electrospun PLLA fibres were investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Take-up velocity was found as a dominant parameter to induce a highly ordered molecular structure in the electrospun PLLA fibres compared to solution conductivity and polymer concentration, although these two parameters played an important role in controlling the fibre diameter. A collecting method of a single nanofibre by an electrospinning process was developed for the tensile tests to investigate structure-property relationships of the polymer nanofibres. The tensile test results indicated that higher take-up velocity caused higher tensile modulus and strength due to the ordered structure developed through the process.     

Emulsion electrospun vascular endothelial growth factor encapsulated poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid-<Emphasis Type="Italic">co</Emphasis>-ε-caprolactone) nanofibers for sustained release in cardiac tissue engineering

Emulsion electrospinning is a novel approach to fabricate core–shell nanofibers, and it is associated with several advantages such as the alleviation of initial burst release of drugs and it protects the bioactivity of incorporated drugs or proteins. Aiming to develop a sustained release scaffold which could be a promising substrate for cardiovascular tissue regeneration, we encapsulated vascular endothelial growth factor (VEGF) with either of the protective agents, dextran or bovine serum albumin (BSA) into the core of poly(l-lactic acid-co-ε-caprolactone) (PLCL) nanofibers by emulsion electrospinning. The morphologies and fiber diameters of the emulsion electrospun scaffolds were determined by scanning electron microscope, and the core–shell structure was evaluated by laser scanning confocal microscope. Uniform nanofibers of PLCL, PLCL–VEGF–BSA, and PLCL–VEGF–DEX with fiber diameters in the range of 572 ± 92, 460 ± 63, and 412 ± 61 nm, respectively were obtained by emulsion spinning. The release profile of VEGF in phosphate-buffered saline for up to 672 h (28 days) was evaluated, and the scaffold functionality was established by performing cell proliferations using human bone marrow derived mesenchymal stem cells. Results of our study demonstrated that the emulsion electrospun VEGF containing core–shell structured PLCL nanofibers offered controlled release of VEGF through the emulsion electrospun core–shell structured nanofibers and could be potential substrates for cardiac tissue regeneration.     

Electrospun polyurethane and soy protein nanofibres for wound dressing applications

In this report, a novel wound dressing material has been woven by electrospinning technique and tested for its various properties. For the nanofibre mat, a mixture of polyurethane (PU) and soy protein isolate (SPI) was electrospun in conjugation with zinc oxide nanoparticles (ZnO Nps) and ciprofloxacin hydrochloride (CipHCl) to produce fibrous mats viz. PU/SPI/ZnO and PU/SPI/CipHCl. An optimum ratio (1 : 1) of PU/SPI was used as suitable polymeric ratio in order to produce homogenous nanofibres without beads having an average diameter in the range of 300–350 nm. The electrospun nanofibre‐based mats were characterised using X‐ray diffraction, Fourier transform infrared spectroscopy, ultraviolet‐visible spectroscopy, thermogravimetric analysis and scanning electron microscope. The mechanical properties of the nanofibrous mats were tested using universal testing machine. The wettability analysis was done using the contact angle measurement based on the sessile drop test. This study revealed that the electrospun PU/SPI‐based nanofibres are non‐sensitizing, non‐allergic and non‐toxic and that it can be used as a peculiar wound healing material.Inspec keywords: polymer fibres, nanofibres, nanomedicine, biomedical materials, wounds, electrospinning, zinc compounds, II‐VI semiconductors, wide band gap semiconductors, nanoparticles, nanofabrication, X‐ray diffraction, Fourier transform spectra, infrared spectra, ultraviolet spectra, visible spectra, thermal analysis, scanning electron microscopy, wetting, contact angle, toxicologyOther keywords: electrospun polyurethane nanofibres, soy protein nanofibres, wound dressing applications, electrospinning, nanofibre mat, soy protein isolate, zinc oxide nanoparticles, ciprofloxacin hydrochloride, X‐ray diffraction, Fourier transform infrared spectroscopy, ultraviolet‐visible spectroscopy, thermogravimetric analysis, scanning electron microscope, mechanical properties, universal testing machine, wettability, contact angle measurement, sessile drop test, nonsensitizing nanofibres, nonallergic nanofibres, nontoxic nanofibres, wound healing material, wavelength 300 nm to 350 nm, ZnO     

Polyamide 6.9 nanofibres electrospun under steady state conditions from a solvent/non-solvent solution

Nanofibres can be processed into several high-end applications due to their unique characteristics, especially when based on a diversity of polymers with specific properties. This, however, requires that the nanofibrous structures are produced in a highly reproducible way. The article gives focus to polyamide (PA) 6.9, a less exploited PA though with interesting properties such as a very low moisture absorption. To trace and understand the dominant parameters that allow for the aimed reproducible characteristics, the influence of the solution parameters on the steady state behaviour during electrospinning as well as the resultant fibre morphology is followed by scanning electron microscopy and differential scanning calorimetry. Results show a significant effect of the amount of non-solvent acetic acid, added to the solvent formic acid, on the steady state behaviour and the fibre morphology. The non-solvent acetic acid broadens the steady state window by making the electrospin solutions more suitable to obtain uniform and reproducible nanofibrous structures with a narrow nanofibre diameter distribution. The mixture of the solvent formic acid and the non-solvent acetic acid strongly contributes to the future potentials of PA 6.9 nanofibres, with its leading to a smaller fibre distribution and moreover highly reproducible in time.     

Ferulic acid‐loaded collagen hydrolysate and polycaprolactone nanofibres for tissue engineering applications

There is a great need for the progress of composite biomaterials, which are effective for tissue engineering applications. In this work, the development of composite electrospun nanofibres based on polycaprolactone (PCL) and collagen hydrolysate (CH) loaded with ferulic acid (FA) for the treatment of chronic wounds. Response Surface Methodology (RSM) has been applied to nanofibres factor manufacturing assisted by electrospinning. For wound healing applications, the authors have created the efficacy of CH, and PCL membranes can act as a stable, protective cover for wound, enabling continuous FA release. The findings of the RSM showed a reasonably good fit with a polynomial equation of the second order which was statistically acceptable at P  < 0.05. The optimised parameters include the quantity of hydrolysate collagen, the voltage applied and the distance from tip‐to‐collector. Based on the Box–Behnken design, the RSM was used to create a mathematical model and optimise nanofibres with minimum diameter production conditions. Using FTIR, TGA and SEM, optimised nanofibres were defined. In vitro, cytocompatibility trials showed that there was an important cytocompatibility of the optimised nanofibres, which was proved by cell proliferation and cell morphology. In this research, the mixed nanofibres of PCL and CH with ferulic could be a potential biomaterial for wound healing.Inspec keywords: tissue engineering, polymer fibres, wounds, electrospinning, nanofibres, response surface methodology, cellular biophysics, proteins, molecular biophysics, scanning electron microscopy, biomedical materials, nanomedicine, nanocomposites, nanofabrication, Fourier transform infrared spectraOther keywords: wound healing applications, PCL membranes, stable cover, protective cover, continuous FA release, RSM, optimised parameters, hydrolysate collagen, mathematical model, optimised nanofibres, polycaprolactone nanofibres, tissue engineering applications, composite biomaterials, composite electrospun nanofibres, collagen hydrolysate, ferulic acid, chronic wounds, Response Surface Methodology, nanofibres factor     

Functionalization of electrospun magnetically separable TiO<Subscript>2</Subscript>-coated SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanofibers: strongly effective photocatalyst and magnetic separation

Magnetically separable TiO₂-coated SrFe₁₂O₁₉ electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO₂-coated SrFe₁₂O₁₉ fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant dye solution, MB in a photochemical reactor. In contrast to pure TiO₂ fibers, the TiO₂-coated SrFe₁₂O₁₉ fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe₁₂O₁₉ not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore, these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution of treated water.     

Preparation and characterisation of zein/polyphenol nanofibres for nerve tissue regeneration

Bridging strategies are required to repair peripheral nerve injuries that result in gaps >5–8 mm. Limitations such as donor‐site morbidity and size mismatches with receptor sites for autografts, together with immunological problems associated with allografts and xenografts, have created an increased interest in the field of manufactured nerve guide conduits. In this study, zein, a plant protein‐based polymer, was electrospun to prepare nanofibrous mats. An important challenge with zein mats is the rapid change from fibre to film under aqueous conditions. Tannic acid (TA), which is a polyphenol, was selected to prepare a blend of zein/TA with different weight ratios to investigate its effect on the wetting resistance of nanofibres. The electrospun mats were characterised and evaluated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Also, degradation and mechanical properties of the mats were studied. Results showed that TA had a significant effect on the resistance to film formation in nanofibres. Moreover, the degradation and elongation at break of mats were increased with increase in TA concentration. For the investigation of the peripheral nerve regeneration potential, Schwann cells were selected for cytotoxicity evaluation by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5 diphenyltetrazolium bromide assay and cell morphology by SEM. Schwann cells had good biocompatibility with zein/TA blends (%) of 90/10 and 80/20.Inspec keywords: polymer fibres, biomedical materials, electrospinning, cellular biophysics, tissue engineering, proteins, molecular biophysics, neurophysiology, nanofibres, injuries, nanomedicine, toxicology, scanning electron microscopy, nanofabrication, polymer blends, polymer films, wetting, Fourier transform infrared spectra, elongationOther keywords: SEM, Schwann cells, nerve tissue regeneration, peripheral nerve injuries, donor‐site morbidity, size mismatches, receptor sites, immunological problems, allografts, xenografts, manufactured nerve guide conduits, plant protein‐based polymer, nanofibrous mats, zein mats, aqueous conditions, tannic acid, wetting resistance, electrospun mats, scanning electron microscopy, film formation, TA concentration, peripheral nerve regeneration potential, cell morphology, weight ratios, zein‐polyphenol nanofibres, electrospinning, zein‐TA blends, Fourier transform infrared spectroscopy, mechanical properties, elongation‐at‐break, cytotoxicity evaluation, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5 diphenyltetrazolium bromide assay, biocompatibility     

Silica nanofibers based impedance type humidity detector prepared on glass substrate

Impedance type relative humidity detector is fabricated by depositing electrospun silica nanofibers on glass substrate. The silica nanofibers with an average diameter ∼150 nm and length ∼100 μm were used. Thermogravimetric and differential scanning calorimetric analysis confirm that the accurate annealing temperature is 500 °C for complete removal of PVP. Humidity detecting devices were fabricated by defining titanium electrodes on top of the silica nanofibers. The performance of silica nanofibers humidity detectors was tested by AC electrical measurements at 40–90% relative humidity. The response and the recovery times were 5 s and 3 s, respectively, between 40% and 90% relative humidity. Contribution of dipoles, space charge polarization, relaxation of these dipoles and low frequency dispersion phenomenon were observed during impedance measurements.     

Investigation of microhardness and thermo-electrical properties in the Sn–Cu hypereutectic alloy

Sn–3 wt% Cu hypereutectic alloy was directionally solidified upward with different growth rates (2.24–133.33 μm/s) at a constant temperature gradient (4.24 K/mm) and with different temperature gradients (4.24–8.09 K/mm) at a constant growth rate (7.64 μm/s) in the Bridgman-type growth apparatus. The measurements of microhardness of directionally solidified samples were obtained by using a microhardness test device. The dependence of microhardness HV on the growth rate (V) and temperature gradient (G) were analyzed. According to these results, it has been found that with the increasing the values of V and G the value of HV increases. Variations of electrical resistivity (ρ) and electrical conductivity (σ) for casting samples with the temperature in the range of 300–500 K were also measured by using a standard dc four-point probe technique. The variation of Lorenz coefficient with the temperature for Sn–3 wt% Cu hypereutectic alloy was determined by using the measured values of electrical and thermal conductivities. The enthalpy of fusion for same alloy was determined by means of differential scanning calorimeter from heating trace during the transformation from eutectic liquid to eutectic solid.