Continuous yarns from electrospun fibers

A technique for making continuous uniaxial fiber bundle yarns from electrospun fibers is described. The technique consists of spinning onto a water reservoir collector and drawing the resulting non-woven web of fibers across the water before collecting the resulting yarn. Yarns from electrospun fibers of poly(vinyl acetate), poly(vinylidene difluoride) and polyacrylonitrile are used to illustrate the process of yarn formation and fiber alignment within the yarn. A theoretical production rate of 180 m of yarn per hour for a single needle electrospinning setup makes the process suitable for lab-scale production of electrospun yarns.     

PEG-PLA-PCL based electrospun yarns with curcumin control release property as suture

This work presents an interesting method using an electrospinning process to fabricate suture yarns loaded with curcumin to achieve reasonable mechanical properties as well as tunable drug release behavior. Different structures including different yarn counts and twists as well as core-sheath structures were used to adjust drug release properties along with improving the yarn's mechanical properties. The core parts were made of polycaprolactone and the sheath parts were made of polyethylene glycol, polylactic acid, and polycaprolactone. Drugs can be incorporated in both parts based on the required condition and application. Electrospun yarns were compared using both structural properties and their drug release profiles as metrics. The results of comparing drug release profiles of six electrospun yarns with different yarn counts and twists showed that yarns with finer fiber diameters in the core part have more drug release as well as more initial release. Overall evaluations showed that core-sheath drugloaded yarn with appropriate physical and mechanical properties can be a useful material as a drug delivery system to the site of damaged tissue. It can also be concluded that the amount and duration of drug release can be controlled using the structural parameters of electrospun yarns as an engineering tool for designing suture yarns with required properties.     

Development of Electrospun Composite Fibers in Multiscale Structure and Investigating the Performance on Proliferation and Osteogenic Differentiation of ADSCs

Electrospun composite membranes in multiscale structures are developed for bone tissue engineering. Aligned polycaprolactone (PCL) fibers entrapping CA‐HAp microparticles (containing CaCO₃, hydroxyapatite, and casein in a hierarchical organization) are electrospun to find whether synergistic effects of fiber alignment and CA‐HAp microparticles on improving osteogenic differentiation can be obtained. CA‐HAp microparticles are in a spherical morphology of 1.42 ± 0.26 µm. Their presence increases fiber diameter and does not significantly affect fiber alignment. On all membranes, adipose derived stem cells (ADSCs) from humans spread very well. On a random group, cells distribute randomly and the presence of CA‐HAp microparticles facilitates cell proliferation, especially for the one at CA‐HAp/PCL 50 wt%; the one at CA‐HAp/PCL 20 wt% shows significantly much higher alkaline phosphatase (ALP) activity (112.0% higher) than the pure PCL membrane. On aligned samples, cells align along fibers and expression of ALP is enhanced. However, at the same composition (CA‐HAp/PCL 20 wt%), the random sample has much higher ALP activity than the aligned sample. The expressions of osteogenic marker genes are also evaluated. Combining the results and the applicability of membranes together, the random membrane at CA‐HAp/PCL 20 wt% is the best candidate for bone tissue engineering.     

Shape memory polyurethane-based electrospun yarns for thermo-responsive actuation

Electrospun nanofibrous yarns of shape memory polyurethane (SMPU)-based nanofibers were successfully prepared. The electrospun yarns were analyzed to assess the dependence of mechanical and shape memory properties on the yarn twist angle. The yarn with a 60° twist angle has high compactness and density, leading to increased tensile strength, elastic modulus, and strain energy. In addition, this yarn shows a significant improvement in the shape memory recovery stress compared with the non-twisted SMPU nanofibers. Moreover, thermal stimuli allowed for the 60° twisted yarn to lift a load that is 103 times heavier than itself. This yarn had a shape recovery stress of 0.61 MPa and generated a 7.95 mJ recovery energy. The results suggest the electrospun yarns could be used as actuators and sensing devices in the medical and biological fields.     

Effect of fiber structure on the properties of the electrospun hybrid membranes composed of poly(ε‐caprolactone) and gelatin

To elucidate the effect of fiber structure on the properties of the electrospun gelatin/PCL hybrid membranes, three types of fibers with different structures, i.e., core‐shell, blend, and mixed fibers were fabricated. The crystallinity, wettability, swelling degree, and mechanical properties of the hybrid membranes were compared. It was found that the crystalline characteristics of PCL in the core‐shell fibers were different from the fibers fabricated by the other two methods. That is, the orientation degree of the PCL chains in the core‐shell fibers was higher than that in both blend and mixed fibers. The wettability of the hybrid membrane was dependent on both the composition and structure of the electrospun fibers. Blended fibers exhibited the highest hydrophobicity because of the enrichment of PCL at the fiber surface. Contrarily, the mixed fibers possessed the highest mechanical strength of 3–5.18 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Controllable Aligned Nanofiber Hybrid Yarns with Enhanced Bioproperties for Tissue Engineering

Electrospun nanofibers have large surface area, high porosity, and controllable orientation while conventional microfibers have appropriate mechanical properties such as stiffness, strength, and elasticity. Therefore, the combination of nanofibers and microfibers can provide building elements to engineer biomimetic scaffolds for tissue engineering. In this study, a core–shell structured fibrous structure with controllable surface topography is created by electrospinning polycaprolactone (PCL) nanofibers onto polyglycolic acid (PGA) microfibers. The surface morphology, surface wettability, and mechanical properties of the resultant core–shell structure are characterized. FE‐SEM images reveal that the orientation of PCL nanofibers on the yarn surface can be tuned by a fiber collector and rotating disks. Benefiting from the introduction of a shell of aligned PCL nanofibers on the core of PGA yarn, the uniaxially aligned PCL nanofiber–covered yarns (A‐PCLs) exhibit higher hydrophilicity, porosity, and mechanical properties than the core PGA yarns. Moreover, A‐PCLs promote the adhesion and proliferation of BALB/3T3 (mouse embryonic fibroblast cell line), and guide cell growth along the biotopographic cues of the PCL nanofibers with controllable alignment. The developed core–shell yarn having both the desired surface topography of PCL nanofibers and mechanical properties of PGA microfibers demonstrates great potential in constructing various tissue scaffolds.     

Understanding the relation between structural and mechanical properties of electrospun fiber mesh through uniaxial tensile testing

Polymeric electrospun fibers have the potential to be utilized for a variety of applications such as tissue engineering, filtration, and textiles, owing to their high surface area per unit mass. However, these applications have some form of dependency on the mechanical properties of fiber meshes. Therefore, the current study is aimed at understanding the mechanical behavior of electrospun fiber systems at different length scales in order to establish a correlation between their structure and mechanical properties. Micro‐/nano‐fiber meshes of polystyrene were fabricated by the process of electrospinning and were subjected to uniaxial tensile testing. High‐resolution imaging during tensile testing revealed the macroscopic and microscopic structural evolution of these fibers. Further, the dependence of tensile strength, % elongation, and toughness of fiber meshes on the orientation of the fibers were also experimentally observed. The continuum mechanics simulation studies of fiber meshes with different orientations corroborated well with these experimental studies. Comprehensively, these studies demonstrated the changes in mechanical behavior of electrospun fiber meshes owing to the reorientation and alignment of fibers in meshes at microscopic and macroscopic length scale during tensile testing. Such study can be extrapolate for the design and fabrication of load‐bearing tissues scaffolds, and filtration devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45012.     

Control of electrospun mat width through the use of parallel auxiliary electrodes

Electrospinning offers a versatile way to produce one-dimensional micrometer or nanometer materials; however, electrospun fibers are typically collected in a random orientation limiting their applications. In the present study, we have expanded upon a technique used to align fibers for control of the fiber distribution during the spinning process through the use of auxiliary counter electrodes. The electrostatic force imposed by the auxiliary electrodes provides a converged electric field, which affords control over the distribution of the fibers on the rotating collector surface. Experimental results demonstrate that the width of electrospun mats can be decreased dramatically when parallel auxiliary electrodes are employed at the collector. There was no apparent difference in the average diameters of the electrospun fibers as a result of the additional auxiliary electrodes, but the fiber distribution density in terms of mat width was greatly improved. Thus, the use of auxiliary counter electrodes at the rotating collectors provides a viable method of converging and controlling the deposition of electrospun fibers.     

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     

Implication of stable jet length in electrospinning for collecting well-aligned ultrafine PLLA fibers

Stable jet based electrospinning (SJES) has recently emerged as a straight-forward approach for the continuous fabrication of well-aligned ultrafine fibers and fiber assemblies. This article reports on the influences of some pivotal solution parameters including solvent, polymer molecular weight, and concentration on the formation of a stable jet length (SJL) in electrospinning of a biodegradable polymer, poly(l-lactide acid) (PLLA). Our results reveal that enhanced critical SJL can be achieved at lower solvent dielectric constant and higher viscoelasticity of solutions contributed by the molecular weight and concentration, beneficial for achieving higher degree of fiber alignment. Moreover, hierarchical orderliness including the macroscopic fiber alignment, the elongation along the fiber direction of microscopic pores on the fiber surface and the molecular orientation within the electrospun PLLA fibers, can be modulated by the SJL. The molecular orientation and crystallinity of the aligned PLLA fibers from SJES increased with increasing the SJLs. Also, the measured tensile properties data suggest a positive trend associated with the SJL. This study thus allows establishing a solid correlation of SJL with respect to the macroscopic alignment, internal molecular structural development, and mechanical performance of the electrospun ultrafine PLLA fibers pertaining to the SJES.     

碳纤维直径对结构和性能的影响

借助于光学显微镜、扫描电镜和单丝的机械、电性能测试,探讨了PAN原丝直径对预氧丝和碳纤维模截面结构、碳纤维抗张强度、电阻率的影响。结果表明:预氧丝的芯直径随丝的直径增大而增大;粗碳纤维的结构不均匀性比细纤维严重,且在较粗的碳纤维横截面上会出现中空。在一束碳纤维中,随着纤维直径增大,单丝抗张强度下降,电阻率上升。     

Electrospinning of Tough and Elastic Liquid Crystalline Polymer–Polyurethane Composite Fibers: Mechanical Properties and Fiber Alignment

Tough and elastic microfiber composites composed of an elastic polyurethane (Hydrothane) and a liquid crystalline polymer (Vectran) are fabricated via electrospinning. The composite fibers (HVC) are examined as a function of the mixing ratio of the polymers and evaluated on the bases of fiber formation, morphology, thermal properties, mechanical performance, and fiber alignment. The fiber diameters of the HVCs decrease as the content of Vectran increases. When the fibers are aligned via a rotating target, they have even smaller diameters and increased uniformity than when a static target is employed. Surprisingly, the aligned fibers’ mechanical properties are different than those of random orientation; the HVC fibers of random orientation display increases in strength, toughness, and elastic modulii when increasing amounts of Vectran are incorporated in the fibers. The aforementioned mechanical properties of the aligned fibers decrease somewhat as the content of Vectran is increased. Further, the durability of the aligned fibers is examined by extensional durability tests over ten cycles. The tests indicate that the HVC fibers are very durable and can function as tunable, tough, and elastic fibrous polymer scaffolds and have potential applications in high‐performance composites, polymeric filtration devices, and fibrous bioengineering materials.     

Impact of substrate geometry on electrospun fiber deposition and alignment

Aligned, uniform fiber matrixes are highly desirable in numerous engineering and physical science applications. Here, modified electrospinning (ES) deposition substrates (paired and in parallel) are explored to achieve rapid preparation of multiple topographies. Three ES substrates with well‐defined geometries (rectangular, concave, and E‐shaped) were investigated (arranged in parallel) for their impact on fiber size, morphology, orientation, and cell behavior. The results indicate fiber alignment and orientation can be improved and modulated based on the substrate geometry. In addition, altering the interdistance space between various parallel substrates has a clear impact on fiber diameter size and alignment (random, aligned, and perpendicular orientation). Electric field simulations based on substrate geometries show greater probable regions of aligned electric field vectors and distribution, which indicates the most likely deposition attributes of electrospun PCL fibers. Fibrous PCL membranes were biocompatible, and cell growth and guidance were along the fiber path, with evidence of branching at intersecting fibers for multiaxial fibrous topographies. These findings show that the substrate geometry can be optimized to effectively assemble multiaxial layered and well‐aligned fibers in a controlled fashion, which is ideal to support several application developments dependent on fiber topography, integrity, and morphology. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44823.     

The influence of process parameters on the properties of electrospun PLLA yarns studied by the response surface methodology

Poly (l ‐lactide) (PLLA) fibrous yarns were prepared by electrospinning of polymer solutions in 2,2,2‐trifluoroethanol. Applying spinning from two oppositely charged needles the spontaneous formed triangle of fibers at a grounded substrate could be assembled into fibrous yarns using a device consisting of a take‐up roller and twister. The effect of processing parameters on the morphology, diameter and mechanical properties of PLLA yarns was investigated by the response surface methodology (RSM). This method allowed evaluating a quantitative relationship between polymer concentration, voltage, take‐up rate and distance between the needles' center and the take‐up unit on the properties of the electrospun fibers and yarns. It was found that at increasing concentrations up to 9 wt % uniform fibers were obtained with increasing mean diameters. Conversely, the fiber diameter decreased slightly when the applied voltage was increased. The take‐up rate had a significant influence on the yarn diameter, which increased as the take‐up rate decreased. The tensile strength and modulus of the yarns were correlated with these variables and it was found that the polymer concentration had the largest influence on the mechanical properties of the yarns. By applying the RSM, it was possible to obtain a relationship between processing parameters which are important in the fabrication of electrospun yarns. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41388.     

Structure and properties of electrospun poly(vinylidene fluoride)/polycarbonate membranes after hot‐press

Poly(vinylidene fluoride) (PVDF)/polycarbonate (PC) dispersed solutions were electrospun into ultrafine core/shell fibers and modified by hot‐press. Morphology, tensile properties, porosity, and liquid absorption of the electrospun membranes as well as the crystallinity of PVDF were examined before and after hot‐press. Results showed that the tensile strength and tensile modulus of the electrospun membranes increased after hot‐press, especially when poly(methyl methacrylate) (PMMA) or benzyl triethylammonium chloride (BTEAC) was introduced for the formation of distinct core/shell fiber structure. The elongation of the hot‐pressed electrospun PVDF/PC membrane with addition of BTEAC was also significantly enhanced by reason of the clearest core/shell structure. The crystallinity of PVDF did not change too much before and after hot‐press, however the porosity and liquid absorption of the hot‐pressed electrospun membranes decreased to about 58% and around 75–90%, respectively, with no significant differences between PVDF/PC, PVDF/PC/PMMA, and PVDF/PC with BTEAC membranes. This study could be an example of electrospun membranes in multi‐polymer components and it could be extended to other systems of electrospinning for applications in filtration and so on. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhanced mechanical properties of multilayer nano‐coated electrospun nylon 6 fibers via a layer‐by‐layer self‐assembly

We reported the mechanical properties of the polyelectrolyte multilayer nano‐coated electrospun fiber mats with different number of layers. Multilayer nano‐coatings composed of layers of PSS and PAH were successfully deposited onto electrospun nylon 6 fibers via layer‐by‐layer self‐assembly. Compared with pure nylon 6 fibers, the morphology of polyelectrolyte multilayer coated nylon 6 fibers was uniform and smooth. The mechanical properties of polyelectrolyte multilayer coated random and aligned nylon 6 fibers were remarkably enhanced. Moreover, it was found that the higher degree of alignment resulted in higher tensile strength, suggesting the combined effects of the alignment, the surface nanocoating and the formation of internal networks of polyelectrolytes on nylone 6 fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Direct measurement of aerosol glass fiber alignment in a DC electric field

We report non-conducting aerosol fiber (i.e., glass fiber) alignment in a DC electric field. Direct observation of fiber orientation state is demonstrated and quantitative analysis of fiber alignment is made using phase contrast microscopy in four different conditions: (i) dry air and naturally charged fibers, (ii) humid and naturally charged, (iii) humid and neutralized (Boltzmann charge distribution), and (iv) humid and neutralized with an electrostatic precipitator upstream electrodes (i.e., non-charged). The glass fiber aerosols generated by a vortex shaking method were conditioned using a Po-210 neutralizer or humidifier and were provided into a test unit where cylindrical or parallel plate electrodes are used and high voltage is applied to them. Fibers were collected on a filter immediately downstream from the electrodes and their images were taken through an optical microscope to visualize the fiber orientation and measure the alignment angles and lengths of the fibers. The results showed that under all four conditions tested, airborne glass fibers could be aligned to the electric field with different alignment quality, indicating that the glass fibers can be polarized in a steady electric field. In humid air, the fiber alignment along the field direction was observed to be much better and the number of uniform background particles (i.e., randomly oriented fibers) in angular distributions is smaller than that in dry air. Also, it was found that charged fibers in humid air could be better aligned with negligible uniform background than neutralized and non-charged fibers. Possible mechanisms about humidity and charge effects on enhanced fiber alignment are discussed to support the observations. The results indicate that the enhancement of alignment in an electric field would be possible in humid air for other non-conducting fibrous particles having surface chemistry similar to glass fibers.     

Effect of Geometrical Parameters on Piezoresponse of Nanofibrous Wearable Piezoelectric Nanofabrics Under Low Impact Pressure

Piezoelectric polymers are potential energizers for wearable electronics due to the possibility of developing their yarns for various textile products. The present study is aimed at understanding the effect of geometrical parameters, viz., yarn linear density (measured as Tex), twist per meter (TPM), plying, as well as weft and warp density on the piezoelectric voltage of electrospun yarns of polyvinylidene fluoride (PVDF) polymer and poly[(vinylidene fluoride)-co-trifluoroethylene] [P(VDF-TrFE)] copolymer. Yarns are developed by twisting and plying electrospun nanofibers and their mechanical and piezoelectric properties are systematically investigated. Relative advantages of the yarns of the copolymer with respect to PVDF in both aligned and random fiber geometries are evaluated. The studies show that piezoresponse of the woven nanogenerators can be enhanced by decreasing Tex and increasing the TPM, the plying number, and the fabric density. A record piezovoltage of ≈2.5 V is achieved through this work. The results of the present work can be used for the fabrication of flexible and breathable nanogenerators or sensors.     

捆绑纱对预定向经编织物性能的影响

通过用玻璃纤维／涤纶捆绑纱及不同经编组织结构,研究捆绑纱对预定向经编织物性能的影响。结果表明,玻纤可用于捆绑纱组织中,其编织后强度比涤纶纱高33．3％。玻纤捆绑纱可改善树脂对织物的浸渍性,降低最终复合材料的孔隙率,提高复合材料的拉伸和剪切等力学性能。不同的捆绑纱组织结构对复合材料的力学性能影响显著,玻纤做捆绑纱时,经平组织比编链组织复合材料的经向拉伸强度高7．97％,弯曲强度高约5％。