Morphological and mechanical properties of drawn poly(l‐lactide) electrospun twisted yarns

In this study, the continuous twisted PLLA yarns were produced using an electrospinning device consists of two oppositely charged nozzles. The electrospinning process was performed at different twist rates. The electrospun twisted yarns were drawn at different extension ratios of 50% and 100% and their morphological and mechanical properties of post‐drawn yarns were investigated. The morphological studies at all twist rates shown that uniform and smooth fibers without any bead were formed. Increasing the twist rate up to 240 rpm resulted to a decrease in the average diameter of the fibers in the yarn structure. After uniaxially drawing of the yarns, the average diameter of fibers and thus the yarn diameter decreased. The post‐drawing process enhanced the crystallinity of the fibers in the yarn structure. Furthermore, by increasing the extension ratio, the tensile strength and modulus of yarns increased, while the elongation at break (%) decreased. POLYM. ENG. SCI., 58:1091–1096, 2018. © 2017 Society of Plastics Engineers     

Electrospun poly(L‐lactide)/poly(ε‐caprolactone) blend fibers and their cellular response to adipose‐derived stem cells

Polymer blending is one of the most effective methods for providing new, desirable biocomposites for tissue‐engineering applications. In this study, electrospun poly(L ‐lactide)/poly(ε‐caprolactone) (PLLA/PCL) blend fibrous membranes with defect‐free morphology and uniform diameter were optimally prepared by a 1 : 1 ratio of PLLA/PCL blend under a solution concentration of 10 wt %, an applied voltage of 20 kV, and a tip‐to‐collector distance of 15 cm. The fibrous membranes also showed a porous structure and high ductility. Because of the rapid solidification of polymer solution during electrospinning, the crystallinity of electrospun PLLA/PCL blend fibers was much lower than that of the PLLA/PCL blend cast film. To obtain an initial understanding of biocompatibility, adipose‐derived stem cells (ADSCs) were used as seed cells to assess the cellular response, including morphology, proliferation, viability, attachment, and multilineage differentiation on the PLLA/PCL blend fibrous scaffold. Because of the good biocompatibility and nontoxic effect on ADSCs, the PLLA/PCL blend electrospun fibrous membrane provided a high‐performance scaffold for feasible application in tissue engineering using ADSCs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An investigation into the influence of electrospinning parameters on the diameter and alignment of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibers

Electrospinning is an effective technology for the fabrication of ultrafine fibers, which can be the basic component of a tissue engineering scaffold. In tissue engineering, because cells seeded on fibrous scaffolds with varying fiber diameters and morphologies exhibit different responses, it is critical to control these characteristics of electrospun fibers. The diameter and morphology of electrospun fibers can be influenced by many processing parameters (e.g., electrospinning voltage, needle inner diameter, solution feeding rate, rotational speed of the fiber‐collecting cylinder, and working distance) and solution properties (polymer solution concentration and conductivity). In this study, a factorial design approach was used to systematically investigate the degree of influence of each of these parameters on fiber diameter, degree of fiber alignment, and their possible synergetic effects, using a natural biodegradable polymer, poly(hydroxybutyrate‐co‐hydroxyvalerate), for the electrospinning experiments. It was found that the solution concentration invoked the highest main effect on fiber diameter, whereas both rotational speed of the fiber‐collecting cylinder and addition of a conductivity‐enhancing salt could significantly affect the degree of fiber alignment. By carefully controlling the electrospinning parameters and solution properties, fibrous scaffolds of desired characteristics could be made to meet the requirements of different tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of zein and zein/poly‐L‐lactide nanofiber yarns

Zein and zein/poly‐L ‐lactide (PLLA) nanofiber yarns were prepared by conjugate electrospinning using coupled spinnerets applied with two high electrical voltages of opposite polarities in this article. Structure and morphology of zein yarns were investigated by SEM and X‐ray diffraction. The results showed that zein yarn consisted of large quantity of fibers with diameters ranging from several hundreds nanometers to a few microns, and zein concentration played a significant role on the diameter of nanofibers in yarns. To improve mechanical property of nanofiber yarns, PLLA was then incorporated with zein. Zein/PLLA composite nanofiber yarns conjugate electrospun from solution with concentration of 7.5% (zein, w/v)/7.5% (PLLA, w/v) exhibited tensile strength of 0.305 ± 0.014 cN/dtex. The composite yarns showed better nanofiber alignment along the longitudinal axis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters

In the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Conjugate electrospinning of continuous nanofiber yarn of poly(L‐lactide)/nanotricalcium phosphate nanocomposite

The continuous nanofiber yarns of poly(L ‐lactide) (PLLA)/nano‐β‐tricalcium phosphate (n‐TCP) composite are prepared from oppositely charged electrospun nanofibers by conjugate electrospinning with coupled spinnerets. The morphology and mechanical properties of PLLA/n‐TCP nanofiber yarns are characterized by scanning electron microscope, transmission electron microscope, and electronic fiber strength tester. The results show that PLLA/n‐TCP nanofibers are aligned well along the longitudinal axis of the yarn, and the concentration of PLLA plays a significant role on the diameter of the nanofibers. The thicker yarn of PLLA/n‐TCP composite with the weight ratio of 10/1 has been produced by multiple conjugate electrospinning using three pairs of spinnerets, and the yarn has tensile strength of 0.31cN/dtex. A preliminary study of cell biocompatibility suggests that PLLA/n‐TCP nanofiber yarns may be useable scaffold materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Systematic parameter study for ultra-fine fiber fabrication via electrospinning process

Processing parameters effects on the morphology such as fiber diameter and its uniformity of electrospun polymer nanofibers was investigated. A processing map summarized effects of solutions properties and processing conditions on the electrospun nanofiber morphology was obtained. Polymer concentration, its molecular weight, electrical conductivity of solvents were found as dominant parameters to control the morphology. Based on the systematic parameter study, electrospun PLLA fibers as small as 9 nm were successfully produced.     

Antibacterial antiadhesion membranes from silver‐nanoparticle‐doped electrospun poly(L‐lactide) nanofibers

Electrospun fibrous membranes have been used frequently in biomedical applications, but their simultaneous use as antibacterial agents and in the prevention of cell adhesion on repaired tendons after injury has not been investigated. In this study, silver‐nanoparticle (SN)‐loaded poly(L ‐lactide) (PLLA) fibrous membranes were prepared by the electrospinning of SNs into PLLA fibers. Micrograph results showed that these membranes were composed of electrospun fibers and that the fibers were incorporated with SNs. From the results of X‐ray diffraction and thermogravimetry, we concluded that the SNs were physically mixed into the fibers at the desired content. The mechanical properties were not significantly changed. The preliminary antibacterial effects on Staphylococcus epidermidis and Staphylococcus aureus and the synergistic antiproliferative effects of the SN‐loaded PLLA fibrous membranes were observed. Taken together, these results demonstrate that SNs can be directly loaded onto a biodegradable PLLA fibrous membrane via electrospinning to achieve proper material properties with preliminary potential as antibacterial antiadhesion barriers for tendon injury. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrospinning and crosslinking of zein nanofiber mats

Electrospinning processing can be applied to fabricate fibrous polymer mats composed of fibers whose diameters range from several microns down to 100 nm or less. In this article, we describe how electrospinning was used to produce zein nanofiber mats and combined with crosslinking to improve the mechanical properties of the as‐spun mats. Aqueous ethanol solutions of zein were electrospun, and nanoparticles, nanofiber mats, or ribbonlike nanofiber mats were obtained. The effects of the electrospinning solvent and zein concentration on the morphology of the as‐spun nanofiber mats were investigated by scanning electron microscopy. The results showed that the morphologies of the electrospun products exhibited a zein‐dependent concentration. Optimizing conditions for zein produced nanofibers with a diameter of about 500 nm with fewer beads or ribbonlike nanofibers with a diameter of approximately 1–6 μm. Zein nanofiber mats were crosslinked by hexamethylene diisocyanate (HDI). The tensile strength of the crosslinked electrospun zein nanofiber mats was increased significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:380–385, 2007     

Fabrication and properties of PLLA‐gelatin nanofibers by electrospinning

Poly(L ‐lactide acid)‐blend‐gelatin (PLLA‐gelatin) nanofibers were successfully fabricated by means of electrospinning. The different material components characterizing the properties of electrospun PLLA/G nanofibers were measured and the effect of PLLA weight ratios on such properties as morphologies, physical and chemical structure and mechanical profiles were analyzed. It was found that the fibers diameter increases and the ultimate tension‐stress enhances with increased PLLA weight ratio. The analysis of X‐ray diffractometry, differential scanning calorimetry, and Fourier‐transform infrared spectra demonstrated that the resultant nanofibers from electrospinning of PLLA‐gelatin solution are simple blends of these two components. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Point‐bonded electrospun polystyrene fibrous mats fabricated via the addition of poly(butylacrylate) adhesive

Because of poor mechanical strength, applications of electrospun polystyrene (PS) fibrous mats are quite limited. The introduction of various concentrations of poly (butylacrylate) adhesives (PBAs) into PS solutions led to the fabrication of point‐bonded electrospun PS fibrous mats with good mechanical strength. The morphologies of PS/PBA fibers with varying PBA content (0?50 wt%) were investigated using scanning electron microscopy (SEM), and the results were compared with pure PS and PBA fibers fabricated with various solvents. SEM images indicated that point‐bonded PS/PBA fibers were uniformly distributed with an average diameter of 1–2 μm. On increasing concentration of PBA up to 20 wt%, porous PS/PBA fibrous mats were obtained. However, solid films were formed at very high concentrations of PBA. The Young's modulus and tensile strength of PS/PBA fibrous mats increased up to 52.4 and 2.7 MPa, respectively. The resultant enhancement of the mechanical properties of PS fibrous mats on addition of PBA increases the number of potential applications of these materials. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of interface and confinement size on the crystallization behavior of PLLA confined in coaxial electrospun fibers

Poly(l ‐lactide)/polyacrylonitrile (PLLA/PAN) core‐sheath composite fibers were fabricated by coaxial electrospinning. The crystallization behavior of PLLA within the coaxial electrospun fibers was studied by differential scanning calorimetry (DSC). The PLLA/PAN coaxial electrospun fiber with a PLLA diameter of ～32 nm (C1) exhibits a crystallization temperature (T_c) of 22.5 °C higher but a cold‐crystallization temperature (T_cc) of 10 °C lower than bulk PLLA. The crystallinity of C1 fiber is also higher than bulk PLLA. In both isothermal melt‐ and cold‐crystallization, PLLA in C1 fiber crystallizes faster than the bulk PLLA, as revealed by the smaller half crystallization times (t_1/2). The enhanced crystallizability of PLLA in the C1 fiber may be attributed to the increased nuclei number and crystal growth rate induced by the PAN surface, i.e., surface‐induction effect. However, PLLA also suffers a nano‐confinement effect exerted by PAN sheath in the coaxial electrospun fiber, which can suppress PLLA crystallization. When the diameter of PLLA is too small (< 32 nm), the nano‐confinement effect may prevail over the surface‐induction effect, leading to a slower crystallization rate and smaller crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45980.     

Dielectric behavior characterization of a fibrous‐ZnO/PVDF nanocomposite

This study is focused on forming a fibrous‐zinc oxide/polyvinylidine fluoride (ZnO/PVDF) nanocomposite and characterizing its dielectric behavior. The nanocomposite is prepared in two steps. First, a network of nanoscale diameter ZnO fibers is produced by sintering electrospun PVA/Zinc Acetate fibers. Second, the ZnO fibrous nonwoven mat is sandwiched between two PVDF thermoplastic polymer films by hot‐press casting. Scanning electron microscope images of the nanocomposite show that hot‐press casting of the fibrous‐ZnO network breaks the network up into short fibers. The in‐plane distribution of the ZnO fillers (i.e., the short fibers) in the PVDF matrix appears to comply with that of the pristine ZnO fibers before hot‐pressing, indicating that the fillers remain well‐dispersed in the polymer matrix. To the authors' knowledge, the work reported herein is the first demonstration of the use of electrospinning to secure the dispersion and distribution of a network of inorganic fillers. Moreover, processing a fibrous‐ZnO/PVDF flexible composite as described in this report would facilitate material handling and enable dielectric property measurement, in contrast to that on a fibrous mat of pure ZnO. Because of the high surface area of the short ZnO fibers and their polycrystalline structure, interfacial polarization is pronounced in the nanocomposite film. The dielectric constant is enhanced significantly‐up to a factor of 10 at low frequencies compared to the dielectric constant of constituent materials (both bulk ZnO and PVDF), and up to a factor of two compared to a bulk‐ZnO/PVDF composite. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Electrospinning of polyacrylonitrile solutions containing diluted sodiumthiocyanate

The effect of NaSCN salt on the spinnability of polyacrylonitrile (PAN) solutions, its resulting morphology, mechanical property, and the flame resistance of the resulting electrospun nanofibers were studied. The intent was to develop a method to produce nanosized carbon fiber precursors with good properties. Electrospun PAN nanofibers from 9.7–9.9 wt% PAN/sodiumthiocyanate (NaSCN) (aq)/Dimethylformamide (DMF) solutions with 1.0–2.9 wt% NaSCN (aq), and 10–15 wt% PAN/DMF solutions without salt exhibited good spinnability and morphology with no beading in the range of applied voltage (18–20 kV) and take‐up velocity (9.8–12.3 m/s). The relatively high take‐up velocity produced good yarn alignment. The diameter distributions of the PAN nanofibers containing the NaSCN salt were narrower than those of the PAN/DMF nanofibers without the salt. It was determined that the maximum content of salt for production of electrospun PAN nanofibers with good morphology was below 3.8 wt% (40 wt% based on PAN). The salt concentration can positively influence on the narrow diameter distributions of the resulting electrospun fibers. Also, it could be confirmed that the salt effect on mechanical property and flame resistance of electrospun PAN nanofibers. In particular, the elongation of the PAN nanofiber with 2.9 wt% NaSCN (aq) was significantly increased as much as 186% compared with that of 10 wt% PAN nanofiber without the salt. The flame resistance and mechanical properties of the stabilized PAN nanofibers with NaSCN (aq) increased after oxidization process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

The electrospun polyhydroxybutyrate fibers reinforced with cellulose nanocrystals: Morphology and properties

Polyhydroxybutyrate (PHB) has been used in the biomedical field. However, the poor mechanical properties of PHB have limited its application. Here, electrospun fibrous nanocomposite mats reinforced with cellulose nanocrystals (CNCs) were fabricated by using PHB as polymeric matrix. The morphological, thermal, mechanical properties, as well as cytotoxicity were characterized. Increasing the concentration of CNCs caused a decrease in diameter of the electrospun fibers. Moreover, thermal analysis indicated that melting temperature of PHB/CNCs electrospun fibers were improved with the increased CNCs content. The addition of CNCs gradually enhanced the tensile strength till 8 wt % content followed by a gradual decrease at higher CNCs content (12–22 wt %) in tensile strength. The PHB/CNCs electrospun fibers were nontoxic to L‐929 and capable of supporting cell proliferation in all conditions. This study demonstrates that fibrous PHB/CNCs electrospun fibers are cytocompatible and potentially useful mechanical properties for biomedical application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43273.     

Structure and process relationship of electrospun bioabsorbable nanofiber membranes

An electrospinning method was used to fabricate bioabsorbable amorphous poly(d,l-lactic acid) (PDLA) and semi-crystalline poly(l-lactic acid) (PLLA) nanofiber non-woven membranes for biomedical applications. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and synchrotron wide-angle X-ray diffraction/small angle X-ray scattering. SEM images showed that the fiber diameter and the nanostructured morphology depended on processing parameters such as solution viscosity (e.g. concentration and polymer molecular weight), applied electric field strength, solution feeding rate and ionic salt addition. The combination of different materials and processing parameters could be used to fabricate bead-free nanofiber non-woven membranes. Concentration and salt addition were found to have relatively larger effects on the fiber diameter than the other parameters. DSC and X-ray results indicated that the electrospun PLLA nanofibers were completely non-crystalline but had highly oriented chains and a lower glass transition temperature than the cast film.     

Investigation of mechanical properties of unidirectional steel fiber/polyester composites: Experiments and micromechanical predictions

The article introduces steel fiber reinforced polymer composites, which is considered new for composite product developments. These composites consist of steel fibers or filaments of 0.21 mm diameter embedded in a polyester resin. The goal of this investigation is to characterize the mechanical performance of steel fiber reinforced polyester composites at room temperature. The mechanical properties of unidirectional steel fiber reinforced polyester composites (SFRP) are evaluated experimentally and compared with the predicted values by micro‐mechanical models. These predictions help to understand the role of material and process parameters on material properties. Two types of SFRP were studied: polyester resin reinforced by both steel fabric containing unidirectional fibers and steel fibers wound on a metal frame with 0° orientations. The effects of the fiber volume fraction and the role of polymer yarns (weft) on mechanical properties were analyzed through tensile, compressive, and shear tests. These tests were performed as per the standard test procedures. In particular, issues related to processing difficulties, polymer yarns effect on properties, standardized testing, and properties under various loading conditions were addressed. Microscopic observations were analyzed to assess the laminate quality and the macroscopic fracture surfaces of shear test specimens were studied by standard techniques. POLYM. COMPOS., 37:627–644, 2016. © 2014 Society of Plastics Engineers     

Electrospun fibers of poly(l‐lactic acid) containing lovastatin with potential applications in drug delivery

Lovastatin (Merck's Mevacor) is a statin drug designed to lower cholesterol, and reduce the risk of heart attack and stroke. We use electrospinning to combine the biomedical properties of lovastatin with the advantages of electrospun fibers to prepare a composite biomaterial for lovastatin delivery. Poly(l ‐lactic acid) (PLLA), a biodegradable and biocompatible polymer, was co‐spun with lovastatin. Incorporation of lovastatin at 5 or 10 wt % improved fiber alignment and surface smoothness, and increased fiber diameter. Influence of lovastatin on the phase structure (crystal, mobile amorphous, and rigid amorphous fractions) was investigated using scanning calorimetry and synchrotron X‐ray scattering. Addition of lovastatin resulted in increased crystallinity and reduced mobile amorphous fraction. PLLA fibers were characterized in terms of their drug release kinetics in comparison to PLLA film. High drug entrapment efficiency (ranging from 72% to 82%) and appropriate release profiles were achieved. In vitro drug release studies demonstrated that release occurred in two stages: an initial rapid release over the first day and a slower second stage of release which approached a plateau after 7 days. PLLA fibers have a higher release rate than comparable film. Electrospun biomaterial fibers of PLLA provide a promising new release strategy for delivery of lovastatin. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45287.     

Morphology of ultrafine polysulfone fibers prepared by electrospinning

Ultrafine fibers of bisphenol‐A polysulfone (PSF) were prepared by electrospinning of PSF solutions in mixtures of N,N‐dimethylacetamide (DMAC) and acetone at high voltages. The morphology of the electrospun PSF fibers was investigated by scanning electron microscopy. Results showed that the concentration of polymer solutions and the acetone amount in the mixed solvents influenced the morphology and the diameter of the electrospun fibers. The processing parameters, including the applied voltage, the flow rate, and the distance between capillary and collection screen, were also important for control of the morphology of electrospun PSF fibers. It was suggested that uniform ultrafine PSF fibers with diameter of 300–400 nm could be obtained by electrospinning of a 20 % (wt/v) PSF/DMAC/acetone (DMAC:acetone = 9:1) solution at 10–20 kV voltages when the flow rate was 0.66 ml h^?1 and capillary–screen distance was 10 cm. Copyright © 2004 Society of Chemical Industry