Improved survival of cardiac cells on surface modified electrospun nanofibers

Polycaprolactone (PCL) is a popular synthetic polymer used in the field of cardiac tissue engineering (CTE) due to its non-toxic degraded by products and low cost manufacturing method. However, hydrophobic nature of this material limits its wide spread application in different cell interaction processes. Therefore, current study aims to chemically modify PCL made random and aligned nanofibers with collagen coating mimicking the oriented matrix of the cardiac cells. Morphological and chemical properties of the electrospun PCL nanofibers were evaluated by SEM, FTIR, XRD and water contact angle measurement. Results indicated that the anisotropic characteristics of aligned nanofibers promoted cell attachment and alignment, which closely match the requirements of native cardiac cells. Thus, aligned nanofibers could be preferred for cardiac tissue regeneration and defects over random nanofibers.     

Electrospun nanofibrous polycaprolactone scaffolds for tissue engineering of annulus fibrosus

The annulus fibrosus comprises concentric lamellae that can be damaged due to intervertebral disc degeneration; to provide permanent repair of these acquired structural defects, one solution is to fabricate scaffolds that are designed to support the growth of annulus fibrosus cells. In this study, electrospun nanofibrous scaffolds of polycaprolactone are fabricated in random, aligned, and round-end configurations. Primary porcine annulus fibrosus cells are grown on the scaffolds and evaluated for attachment, proliferation, and production of extracellular matrix. The scaffold consisting of round-end nanofibers substantially outperforms the random and aligned scaffolds on cell adhesion; additionally, the scaffold with aligned nanofibers strongly affects the orientation of cells.     

Investigation of the Effect of Thermal Annealing on Poly(3‐hexylthiophene) Nanofibers by Scanning Probe Microscopy: From Single‐Chain Conformation and Assembly Behavior to the Interfacial Interactions with Graphene Oxide

Poly(3‐hexylthiophene) (P3HT) has been widely used in devices owing to its excellent properties and structural features. However, devices based on pure P3HT have not exhibited high performance. Strategies, such as thermal annealing and surface doping, have been used to improve the electrical properties of P3HT. In this work, different from previous studies, the effect of thermal annealing on P3HT nanofibers are examined, ranging from the single polymer chain conformation to chain packing, and the interfacial interactions with graphene oxide (GO) at nanoscale dimensions, by using scanning tunneling microscopy (STM), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). High‐resolution STM images directly show the conformational changes of single polymer chains after thermal annealing. The morphology of P3HT nanofibers and the surface potential changes of the P3HT nanofibers and GO is further investigated by AFM and KPFM at the nanoscale, which demonstrate that the surface potentials of P3HT decrease, whereas that of GO increases after thermal annealing. All of the results demonstrate the stronger interfacial interactions between P3HT and GO occur after thermal treatments due to the changes in P3HT chain conformation and packing order.     

Vascular endothelial and smooth muscle cell culture on NaOH-treated poly(epsilon-caprolactone) films: a preliminary study for vascular graft development

Tissue engineering offers the potential of providing vessels that can be used to replace diseased and damaged native blood vessels. The endothelization of a synthetic vascular graft minimizes the failures associated with blood clotting and platelet activation. The aim of this study was to culture vascular-derived endothelial and smooth muscle cells on both untreated and NaOH-treated poly(epsilon-caprolactone) (PCL) films, a biocompatible and bio-resorbable polymer, and to evaluate the behavior of both cell types as a preliminary study for vascular graft development. PCL films were prepared by hot pressing; characterized by DSC, IR, SEM, and scanning force microscopy; and treated with NaOH to increase the surface hydrophilicity before cell culture. Endothelial and smooth muscle cells, isolated from pig cava vein, were characterized by immunofluorescence and confocal microscopy studies of endothelial nitric oxide synthase and alpha-smooth muscle actin. Good adhesion, growth, viability and morphology of both the endothelial and smooth muscle cells on PCL films were obtained, but a light stimulation of mitochondrial activity was observed during short culture times. NaOH treatment improved the adhesion and enhanced the proliferation in both cell types. This verified the possible use of this modified polymer as a support in the preparation of a synthetic vascular graft. [Diagram: see text] SEM micrograph of smooth muscle cells cultured on NaOH-treated PCL film. (Original magnification: 1000x).     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

Double‐layered composite nanofibers and their mechanical performance

Continuous polymer nanofibers are available through electrospinning, but most have the same structure in their cross section. This article focuses on the fabrication and the structural and mechanical characterization of pencil‐like double‐layered composite nanofibers coaxially electrospun from solutions of two different biodegradable materials, i.e., gelatin and poly(ε‐caprolactone) (PCL). Transmission electron microscopy and water contact angle measurements confirmed that a gelatin inner fiber was wrapped with a PCL outer layer. Possible applications of such nanofibers include a controlled degradation rate when used as a medical device in human body. It has been found that the tensile performance of the composite nanofibers was better than those of both the pure constituent, i.e. gelatin and PCL, nanofibers alone. The ultimate strength and ultimate strain of the composite nanofibers with 7.5% w/v gelatin in the core and 10% w/v PCL as shell were at least 68% and 244% higher, respectively, than those of the same concentration pure gelatin and PCL nanofibers. Thus, a coaxial electrospinning technique as used in this article can be applicable, not only in developing functionalized nanofibers but also in elevating their mechanical property. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2852–2861, 2005     

Core-sheath functional polymer nanofibers prepared by co-electrospinning

Core-sheath polymer nanofibers with optoelectronic materials as the sheath and easily spinnable polymer as the core were prepared by co-electrospinning. Three prototypical systems of polystyrene/poly(p-phenylene vinylene) (PS/PPV), poly(vinyl alcohol)/poly(p-phenylene vinylene) (PVA/PPV) and polystyrene/tris(8-quinolinolato) aluminum (PS/Alq₃) were investigated. The fluorescence microscopy images showed that the resulting nanofibers with uniform morphologies exhibited outstanding emission properties. The core-sheath structures of these nanofibers were observed by TEM investigation. The photoluminescence spectra indicated that the fluorescent properties of these functional core-sheath nanofibers could be influenced by the interaction between core and sheath materials.     

Promotion of Neurite Outgrowth and Extension Using Injectable Welded Nanofibers

We report a general strategy to develop injectable welded nanofibers to facilitate the outgrowth and extension of neurites. In this case, nonwoven mats of uniaxially aligned poly(caprolactone)(PCL) nanofibers were firstly cut into several small pieces with fixed fiber lengths of 25, 50 and 100 μm, respectively, using a cryotome. A tissuelyser was employed to homogenize and disperse the short nanofibers to a homogeneous suspension. By tuning treatment duration from 100 s to 400 s, the temperature of the suspension was brought close to the melting point of PCL. As such, the short nanofibers were welded at their cross points while the fibers far away from the cross points remain the original structures. We showed that the viability of neuroblastoma SH-SY5Y cells and their neurite outgrowth and extension were enhanced with the use of such welded short nanofibers. Taken together, this study provides a simple way to generate injectable welded nanofibers, holding potential in affecting neurite outgrowth and extension for nerve repair, in particular, in the central nervous system.     

Immobilization of anti-CD31 antibody on electrospun poly(ɛ-caprolactone) scaffolds through hydrophobins for specific adhesion of endothelial cells

Hydrophilicity improvement and bioactive surface design of poly(?-caprolactone) (PCL) grafts are of key importance for their application in tissue engineering. Herein, we develop a convenient approach for achieving stable hydrophilic surfaces by modifying electrospun PCL grafts with a class II hydrophobin (HFBI) coating. Static water contact angles (WCA) demonstrated the conversion of the PCL grafts from hydrophobic to hydrophilic after the introduction of amphiphilic HFBI. ATR-FTIR and XPS confirmed the presence of self-assembled HFBI films on the surface of the PCL nanofibers. The biocompatibility of the HFBI-modified PCL grafts was evaluated by cell proliferation in vitro, and by arteriovenous shunt (AV shunt) experiments ex vivo. Anti-CD31 antibody, which is specific for endothelial cells (ECs), was subsequently immobilized on the HFBI-coated PCL scaffolds through protein-protein interactions. This bioactive PCL graft was found to promote the attachment and retention of endothelial cells. These results suggest that this stepwise strategy for introducing cell-specific binding molecules into PCL scaffolds may have potential for development of vascular grafts that can endothelialize rapidly in vivo.     

Nanosegregated polymeric domains on the surface of Fe3O4@SiO2 particles

Multifunctional, biocompatible, and brush‐grafted poly(ethylene glycol)/poly(ε‐caprolactone) (PEG/PCL) nanoparticles have been synthesized, characterized, and used as vehicles for transporting hydrophobic substances in water. For anchoring the polymer mixed brushes, we used magnetic‐silica particles of 40 nm diameter produced by the reverse microemulsion method. The surface of the silica particle was functionalized with biocompatible polymer brushes, which were synthesized by the combination of “grafting to” and “grafting from” techniques. PEG was immobilized on the particles surface, by “grafting to,” whereas PCL was growth by ROP using the “grafting from” approach. By varying the synthetic conditions, it was possible to control the amount of PCL anchored on the surface of the nanoparticles and consequently the PEG/PCL ratio, which is a vital parameter connected with the arrangement of the polymer brushes as well as the hydrophobic/hydrophilic balance of the particles. Thus, adjusting the PEG/PCL ratio, it was possible to obtain a system formed by PEG and PCL chains grafted on the particle's surface that collapsed in segregated domains depending on the solvent used. For instance, the nanoparticles are colloidally stable in water due to the PEG domains and at the same time are able to transport, entrapped within the PCL portion, highly water‐insoluble drugs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2966–2975     

Production of aligned helical polymer nanofibers by electrospinning

A new and simple electrospinning method has been developed for producing aligned helical polymer nanofibers. Aligned helical polycaprolactone (PCL) nanofibers were prepared by this method. The helical fibers were collected by a tilted glass slide. The morphology and loop diameters of the helical structures are dependant on the PCL solution concentration and the loop diameters are in the range of 6.9-14.9 μm for the concentration range of 4.7%-10%. The three-dimensional helical structures were obtained at the high solution concentration of 10%. These helical structures were formed by jet buckling due to mechanical instability when hitting collector surface. Formation of the helical structures is dependent on the obliquity of the tilted glass slide and distance away from the syringe needle. The converging electrical field generated by a tip collector plays an important role in the alignment of the helical structures.     

Electrospinning of polyvinylidene difluoride with carbon nanotubes: synergistic effects of extensional force and interfacial interaction on crystalline structures

Polyvinylidene difluoride (PVDF) solutions containing a very low concentration of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) of similar surface chemistry, respectively, were electrospun, and the nanofibers formed were collected using a modified rotating disk collector. The polymorphic behavior and crystal orientation of the nanofibers were studied using wide-angle X-ray diffraction and infrared spectroscopy, while the nanotube alignment and interfacial interactions in the nanofibers were probed by transmission electron microscopy and Raman spectroscopy. It is shown that the interfacial interaction between the SWCNTs and PVDF and the extensional force experienced by the nanofibers in the electrospinning and collection processes can work synergistically to induce highly oriented beta-form crystallites extensively. In contrast, the MWCNTs could not be well aligned along the nanofiber axis, which leads to a lower degree of crystal orientation.     

Selective localization of graphene oxide in electrospun polylactic acid/poly(ε-caprolactone) blended nanofibers

Despite their immiscibility, blending polylactic acid (PLA) with poly(ε-caprolactone) (PCL) provides an efficient strategy for obtaining a biopolymer blend with tailored properties due to their complementary physical properties. In this study, graphene oxide (GO) was employed as a 2-D nanofiller and nucleating agent to improve the properties of the immiscible PLA/PCL blends at 70/30, 50/50, and 30/70 wt ratios. Nanofibers of PLA/PCL blends and PLA/PCL/GO composites were investigated. It was interesting to find that the GO selectively localized in the minor phase resulting from the phase separation. The selective localization of the GO as the nucleating agent had an influence on the degree of crystallinity and crystalline morphology in the blended composites. This study also demonstrated that the molecular chains in the PLA phase oriented along the fiber axes, while in the PCL phase, the partial crystallites changed their orientation direction to be perpendicular to the fiber axes with the addition of GO.     

Electrospinning of Hyperbranched Poly-L-Lysine/Polyaniline Nanofibers for Application in Cardiac Tissue Engineering

Electrospun polyaniline nanofibers are one of the most promising materials for cardiac tissue engineering due to their tunable electroactive properties. Moreover, the biocompatibility of polyaniline nanofibes can be improved by grafting of adhesive peptides during the synthesis. In this paper, we describe the biocompatible properties and cardiomyocytes proliferation on polyaniline electrospun nanofibers modified by hyperbranched poly-L-lysine dendrimers (HPLys). The microstructure characterization of the HPLys/polyaniline nanofibers was carried out by scanning electron microscopy (SEM). It was observed that the application of electrical current stimulates the differentiation of cardiac cells cultured on the nanofiber scaffolds. Both electroactivity and biocompatibility of the HPLys based nanofibers suggest the use this material for culture of cardiac cells and opens the possibility of using this material as a biocompatible electroactive 3-D matrix in cardiac tissue engineering.     

Single-walled carbon nanotubes embedded in oriented polymeric nanofibers by electrospinning

The electrospinning process was used successfully to embed single-walled carbon nanotubes (SWCNTs) in a poly(ethylene oxide) (PEO) matrix, forming composite nanofibers. Initial dispersion of SWCNTs in water was achieved by the use of an amphiphilic alternating copolymer of styrene and sodium maleate. The resulting dispersions were stable, having a dark, smooth, ink-like appearance. For electrospinning, the dispersions were mixed with PEO solution in an ethanol/water mixture. The distribution and conformation of the nanotubes in the nanofibers were studied by transmission electron microscopy (TEM). Oxygen plasma etching was used to expose the nanotubes within the nanofibers to facilitate direct observation. Nanotube alignment within the nanofibers was shown to depend strongly on the quality of the initial dispersions. Well-dispersed and separated nanotubes were embedded in a straight and aligned form, while entangled nonseparated nanotubes were incorporated as dense aggregates. X-ray diffraction demonstrated a high degree of orientation of the PEO crystals in the electrospun nanofibers with embedded SWCNTs. This result is in pronounced distinction to the detrimental effect of incorporation of multiwalled carbon nanotubes on polymer orientation in electrospun nanofibers, as reported previously.     

Effect of different solvents on poly(caprolactone) (PCL) electrospun nonwoven membranes

Poly(caprolactone) (PCL) is one of biodegradable and biocompatible polymers, which have received significant attention because they are environmentally friendly and are extensively used in biomedical applications. Electrospinning was a straightforward method to produce nanofibers from polymer solutions in a wide submicron range around 100 nm. However, no clear standard had been established for judging whether a solvent of high solubility for a polymer would produce a solution good for electrospinning. Considering the above-mentioned cause, we explored the effect of solvent on fibrous morphology, FT–IR spectra and ¹H NMR spectra, viscosity and shearing strength, differential scanning calorimetry (DSC) of PCL electrospun nonwoven membranes in this article. When NMP and AC were used as the solvent for PCL electrospinning, all of them were composed of smooth and nanosized fibers with similar fiber surface morphologies. Meanwhile, when DCM and CF were used as solvent, there were lots of holes in fibers due to high evaporation. The electrospinnability was good when CA was chosen as solvent due to its lowest viscosity.     

Electrospun poly(3‐hexylthiophene)/poly(ethylene oxide)/graphene oxide composite nanofibers: effects of graphene oxide reduction

In this article, we report on the production by electrospinning of P3HT/PEO, P3HT/PEO/GO, and P3HT/PEO/rGO nanofibers in which the filler is homogeneously dispersed and parallel oriented along the fibers axis. The effect of nanofillers' presence inside nanofibers and GO reduction was studied, in order to reveal the influence of the new hierarchical structure on the electrical conductivity and mechanical properties. An in‐depth characterization of the purity and regioregularity of the starting P3HT as well as the morphology and chemical structure of GO and rGO was carried out. The morphology of the electrospun nanofibers was examined by both scanning and transmission electron microscopy. The fibrous nanocomposites are also characterized by differential scanning calorimetry to investigate their chemical structure and polymer chains arrangements. Finally, the electrical conductivity of the electrospun fibers and the elastic modulus of the single fibers are evaluated using a four‐point probe method and atomic force microscopy nanoindentation, respectively. The electrospun materials crystallinity as well as the elastic modulus increase with the addition of the nanofillers while the electrical conductivity is positively influenced by the GO reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

The effect of collector gap width on the extent of molecular orientation in polymer nanofibers

Electrospun poly(vinylidene fluoride) (PVDF) nanofibers were collected on aluminum foil across a gap with widths that varied in size from 2 to 10 mm. Scanning electron microscopy (SEM) images on fiber bundles showed that in all cases, fibers in the gap were macroscopically aligned across the gap. However, single fiber selected area electron diffraction (SAED) patterns and polarized Fourier Transform Infrared (FTIR) spectra demonstrated that fibers deposited across the gap were also highly aligned at the molecular level with the polymer backbones oriented along the fiber axis and that the extent of molecular orientation increased with the gap width. A possible explanation for this observation is based on the repulsion of similarly charged nanofibers and the simultaneous attraction of these fibers to the oppositely charged gap edges. This provides a plausible model for understanding the deposition kinetics and subsequent molecular orientation as a function of gap size when electrospinning using this method of fiber collection. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 617–623     

Novel mechanism for spinning continuous twisted composite nanofiber yarns

Highly aligned and twisted composite Nylon 6 nanofibers incorporating multiwall carbon nanotubes (MWCNTs) were successfully electrospun, using a novel mechanism. It has been found that; ultrasound combined with high speed shearing is the simplest and most convenient method to improve the dispersion of MWCNTs into a polymer matrix with a certain loading. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to characterize the morphology of nanofibers, the dispersion of MWCNTs and their alignment inside the fiber body. By manipulating the electrical forces during electrospinning and applying mechanical stretching to the electrospun nanofibers, high polymer chain orientation and better alignment of the MWCNTs particles along the fiber axis was achieved. Twist was applied to the nanofibers for providing the required inter fiber lateral cohesion interaction and friction thus, spinning a continuous twisted composite yarn. SEM images show twisted yarns with diameters ranging between 5 and 10 μm. The twist effect of the parallel bundle was investigated by controlling the twist per unit length using a motor speed controller at values of 100, 250, 500, 750 and 1000 rpm. The paper also provides a comprehensive review of various yarn spinning mechanisms of electrospun nanofibers.     

Microstructural evolution and mechanical investigation of hot stretched graphene oxide reinforced polyacrylonitrile nanofiber yarns

To reveal the enhancement effect of graphene oxide (GO) in polymer nanofiber yarns, polyacrylonitrile (PAN)/GO nanofibers with different GO content (0.1‐0.5 wt%) were electrospun. The alignment of PAN chains and GO in nanofibers was enhanced by hot stretching of the yarn in dry conditions. The microstructure of the composite nanofiber yarns was investigated through X‐ray diffraction, polarized Fourier transform infrared spectroscopy and transmission electron microscopy. The results demonstrated that the hot stretching above T_g of PAN precursor lead to the increased orientation‐induced crystallization and alignment of PAN chain and GO. The yarn with 0.1 wt% GO and stretched by 4 times its length obtained the highest strength and modules (310.88 ± 24.68 MPa and 7.24 ± 0.55 GPa), which were 600% and 500% higher than those of the as‐electrospun pure PAN yarn. The most promising tensile properties found in hot stretched yarns with low GO content was because the strong interaction occurred between PAN molecules and oxygen‐containing functional groups. Indirect evidence of GO aggregation was also presented, which adversely affected the mechanical properties at higher GO content. Composite nanofiber yarns were sewable and weavable, and could be used as a new generation of composite reinforcement after pyrolysis.