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.     

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.     

Producing continuous twisted yarn from well‐aligned nanofibers by water vortex

A new technology based on the liquid support system is introduced for fabricating continuous twisted nanofibrous yarn. In this novel technique, the electrospun yarn was collected from the top of the water vortex such that it can be twisted simultaneously during yarn production. Our study demonstrated the feasibility of the technique for producing continuous twisted yarn from well aligned nanofibers. It is shown that the system can be modified to have different yarn counts with various twists. Further, significant improvement can be seen in the strength and strain when nanofibrous yarn is twisted compared to non‐twisted yarn. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effect of twisting on mechanical properties of GF/PP commingled hybrid yarns and UD‐composites

This study was conducted due to the necessity for improving the processability of commingled yarns during textile processing, in particular dense 3D preform weaving. Open structure of the commingled yarns caused higher production stops. As a possible solution, GF/PP commingled yarns with different twisting levels were produced. Effect of twisting on the mechanical properties of commingled yarns and on their compression molded UD composites are determined. Further tests were executed about yarn/yarn and yarn/metal friction of twisted commingled yarns, which are important properties during textile processing. Theoretical approaches such as a yarn model with linear bar elements and lamina equation with an equivalent angle distortion of over‐delivery proved useful to relate the structural parameters and mechanical properties. As a result, twisting did not significantly affect the modulus of elasticity of UD‐composites, however, the tensile strength of UD‐composites were reduced by further processing even without twisting. Therefore, small twisting levels can be applied on commingled yarns to improve processability of dense preforms without significantly affecting the mechanical performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Production,structure and properties of twistless carbon nanotube yarns with a high density sheath

Carbon nanotube web drawn from a vertically aligned carbon nanotube forest is converted into a twistless yarn by a rubbing roller system. The yarn consists of a high packing density sheath with carbon nanotubes lying straight and parallel to the yarn axis and a low density core with many microscopic voids. The rubbing motion causes carbon nanotubes in the surface layers of the yarn to move in opposite directions and consequently large shear strains in the intermediate region tear the partially densified carbon nanotube assembly apart, resulting in the formation of large voids in the yarn core. The specific tensile modulus and sonic velocity of the core-sheath structured, twistless carbon nanotube yarns are significantly higher than that of their corresponding twist-densified yarns. These improvements have been attributed to increased nanotube-to-nanotube contact length in the high packing density sheath and very few carbon nanotubes lying at an angle to the yarn axis.     

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.     

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     

Strain dependence of electrical resistance in carbon nanotube yarns

Carbon nanotube forests or arrays can be drawn into a web and further twisted into threads. These carbon nanotube threads contain thousands of carbon nanotubes in their cross-sections and can be further composed into yarns that consist of one or more threads. The superior mechanical, thermal and electrical properties of carbon nanotubes are not translated into the carbon nanotube yarns. However, carbon nanotube yarns still exhibit relatively high mechanical stiffness and strength, and low electrical resistivity. More importantly, carbon nanotube yarns exhibit piezoimpedance that could be used for sensing purposes. In order to use carbon nanotube yarns as piezoimpedance-based sensors for structural health monitoring, it is necessary to determine the change in impedance of the yarn as a function of its mechanical strain or stress. This paper presents the results of an experimental study on the coupled mechanical response and electrical response in the direct current mode of the carbon nanotube yarn. A behavior consisting of a negative piezoresistive response was encountered during most of the deformation range of the yarn. This response was shown to exhibit a parabolic response and it was followed by a linear positive piezoresistive response that preceded the failure of the yarn.     

Controlled release of doxycycline within core/shell poly(ε-caprolactone)/poly(ethylene oxide) fibers via coaxial electrospinning

The development of fibers with desired drug release properties has gained a high research interest for water-soluble drugs with controlled drug delivery systems obtained by coaxial electrospinning technique. The objective of this study is to achieve the controlled-release of doxycycline hyclate (DOXH) from the fabricated electrospun fibers. In this case, three different electrospun core/shell fibers have been successfully fabricated using this technique and the model drug, DOXH, has been entrapped in the core layers. The results of the structural properties and in vitro release studies have been compared with electrospun monostructural fibers fabricated by conventional electrospinning technique. Scanning electron microscopy and transmission electron microscopy images have proved that the fabricated electrospun fibers have core/shell structures. Fourier transform infrared spectroscopy has shown convenient interaction and compatibility between polymers and the model drug. X-ray diffraction analysis has revealed that all the encapsulated DOXH are transferred into amorphous physical state and lost its crystalline state in the fibers. Moreover, drug release studies have demonstrated that the electrospun core/shell fibers show a better-controlled release than the monostructural fibers. It can be concluded that the fibers obtained by blending hydrophilic and hydrophobic polymers such as poly(ε-caprolactone) and poly(ethylene oxide) in both shell and core sides are promising candidate for controlled drug release.     

Achievement of high surface charge in poly(vinylidene fluoride) fiber yarns through dipole orientation during fabrication

Electrospun fiber materials are of scientific interest for use in multiple application areas. Charged fiber structures show enhanced properties as desired for some of these applications. One factor influencing the charge on the fiber structure that has not been explored is fiber alignment. Electrospun fiber structures, such as membranes, typically consist of randomly oriented fibers. Structural properties of the membranes such as mechanical strength are known to be affected by the random orientation of the fibers. It is suspected that fiber orientation may also affect the charge capacity of charged fiber structures. A few approaches to form electrospun yarns have been reported. Some of these approaches can also cause fibers to preferentially align along the yarn axis instead of assembling into a random structure. In this work, a rotating metal cone was used to collect Poly(vinylidene fluoride) electrospun fibers from which stretched yarns were drawn and twisted into yarns. The alignment of the fibers in the yarns was controllable to a degree that allowed exploration of the effect of alignment on charge. Long continuous oriented or random yarns of relatively uniform thickness were produced at a rate of about 10 m/h. The yarns were polarized by methods of heating, stretching, and poling. The results show that the fiber yarn formation process endows more charges to the fibers compared to the normal fiber membrane electrospinning and post polarization. This provides a facile route for the preparation of enhanced charge-functionalized fiber structures for a wide range of applications.     

Improving the bonding strength of laminated composites by optimizing fabric composition

Delamination is the most common failure mode in laminated composites due to the weaker strength in the through‐the‐thickness direction. Air‐jet texturing is used to produce bulk and loops in the yarn which provides more contact surface between fibers and resin. The development and characterization of core‐and‐effect textured glass yarns and the effect of texturing on the mechanical properties of laminated composites were presented in previous papers. This article describes the optimization of textured composites by varying the type and combination of constituent yarns for improving the mechanical properties. Composites with combinations of various textured yarns and non‐textured yarns were made. It was observed that the composites made from fabrics having non‐textured yarn in the warp and core‐and‐effect textured yarn in the weft had the best combination of mechanical properties. They maintained the tensile and flexure properties of composites with non‐textured yarns but had significantly higher interlaminar shear strength. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Fast Disintegrating Quercetin-Loaded Drug Delivery Systems Fabricated Using Coaxial Electrospinning

The objective of this study is to develop a structural nanocomposite of multiple components in the form of core-sheath nanofibres using coaxial electrospinning for the fast dissolving of a poorly water-soluble drug quercetin. Under the selected conditions, core-sheath nanofibres with quercetin and sodium dodecyl sulphate (SDS) distributed in the core and sheath part of nanofibres, respectively, were successfully generated, and the drug content in the nanofibres was able to be controlled simply through manipulating the core fluid flow rates. Field emission scanning electron microscope (FESEM) images demonstrated that the nanofibres prepared from the single sheath fluid and double core/sheath fluids (with core-to-sheath flow rate ratios of 0.4 and 0.7) have linear morphology with a uniform structure and smooth surface. The TEM images clearly demonstrated the core-sheath structures of the produced nanocomposites. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results verified that quercetin and SDS were well distributed in the polyvinylpyrrolidone (PVP) matrix in an amorphous state, due to the favourite second-order interactions. In vitro dissolution studies showed that the core-sheath composite nanofibre mats could disintegrate rapidly to release quercetin within 1 min. The study reported here provides an example of the systematic design, preparation, characterization and application of a new type of structural nanocomposite as a fast-disintegrating drug delivery system.     

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.     

The influence of solvent type and polymer concentration on the physical properties of solid state polymerized PA66 nanofiber yarn

We investigated the effects of two different solvent types and three solution concentrations on the electrospinning of solid state polymerized polyamide 66 (SSP PA66) nanofiber yarns. Nanofiber yarns were electrospun from SSP PA66 solutions in formic acid and formic acid/chloroform (3/1), using two oppositely metallic spinnerets system. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) were employed to characterize the morphology and properties of the nanofibrous yarns. Experimental results show that adding chloroform to formic acid as a binary solvent increases viscosity of polymer solution and the nanofibers diameter significantly. XRD patterns reveal that the presence of chloroform affects the crystallinity and the mechanical properties of the produced nanofibrous yarns. PA66 nanofiber yarn from 10 wt % formic acid/chloroform (3/1) solution was successfully electrospun with strength and modulus of 120.16 MPa and 1216.27 MPa respectively. It is also shown that the solution concentration has a significant effect on the modulus of the nanofibers yarns. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Technological principles in texturizing polycaproamide yarns

Conclusions Texturization of yarns by the press-chamber method leads to the formation of twists of the flat zig-zag type on smooth yarns. Because of the receipt of crimp, a yarn is obtained with an increased bulk and improved heat-insulating, and hygienic properties.After texturizing, appreciable changes take place in the structure and morphology of elementary filaments. The latter causes a change in the complex of physicomechanical yarn properties.By the use of basic technological texturizing parameters, it is possible to vary the characteristics of the basic specific properties of crimped yarns.Translated from Khimicheskie Volokna, No. 2, pp. 27–34, March–April, 1985.     

Preparation and properties of antibacterial,biocompatible core–shell fibers produced by coaxial electrospinning

Coaxial electrospinning is a method for producing fibrous mats with optional features, such as antibacterial properties, controllable release, and hydrophobicity based on shell materials. Because these features are important in biomedical applications, in this study, biocompatible hydrophobic polymer (polycaprolactone) and hydrophilic polymer [poly(vinyl alcohol)] with silver nanoparticles loaded in the core solution were coaxially electrospun. The effect of silver addition on the conductivity and viscosity of the solutions, chemical structure of the fiber mats, mechanical properties, porosity, hydrophobicity, water vapor transmission rate (WVTR), silver release, and antibacterial properties were investigated. Fibers with silver exhibited less porosity and a lower WVTR and a greater contact angle than the fibers without silver. Furthermore, the core–shell fibers reduced the burst release of silver and successfully prevented the growth of Escherichia coli and Staphylococcus aureus bacteria. Therefore, it seems that these fibers are suitable for providing electrospun mats with long‐term antibacterial properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44979.     

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.     

Effects of Carbon Yarn Size on the Mechanical Properties of Plain Woven C/SiC Composites

The effects of yarn size on the mechanical properties of silicon carbide composites reinforced with a plain woven carbon cloth with two sizes of yarns (1 and 3 k) were investigated. The experimental results show that the composite fabricated with 1 k yarns exhibits greater stiffness and strength than the composite fabricated with 3 k yarns. Microstructural observations revealed the existence of matrix microcracks in both the composites under the as-processed condition due to the large difference of thermal expansion between the fibers and the matrix, which are more severe for the composite with 3 k yarns. The fractured surfaces of the composite with 1 k yarns showed extensive fiber pull-out in contrast to the yarn pull-out in the composite with 3 k yarns. The larger interyarn and intrayarn voids due to difficulties of matrix infiltration in the composite with 3 k yarns represent the primary contribution to the diminished mechanical properties. Unequal yarn sizes give rise to different yarn waviness, which may be another source of difference in the mechanical properties of composites.