Electrospun Polymer Fibers Research Articles

Accessibility of adsorption sites for superfine powdered activated carbons incorporated into electrospun polystyrene fibers

Superfine powdered activated carbon (SPAC) is sub-micron sized activated carbon with superior adsorption kinetics compared to regular powdered activated carbon (PAC) due to the short intraparticle diffusion times. SPAC has recently been demonstrated as an excellent adsorbent; however, subsequent removal of spent SPAC in suspended reactors may be challenging due to its fine size. Thus, SPAC may benefit from immobilization into a macroscopic scaffolding if its adsorptive properties can be preserved. Composition of non-woven electrospun polystyrene (PS) fibers consisting of SPAC is a novel approach to immobilize SPAC; however, the potential losses of adsorption capacity due to polymer-SPAC interactions is still mostly unknown. In this study, SPAC-laden electrospun PS with intentionally tuned SPAC sizes were fabricated for the first time. The centrifugal separation of SPAC generated two different particle sizes with median diameters of 0.30 ± 0.15 µm (SPAC-Fine) and 0.62 ± 0.25 µm (SPAC-Coarse). Both SPAC-Fine and SPAC-Coarse were added to the spinning solution and compared against the PS-only control fibers. Phenanthrene was used as a probe molecule to investigate the accessibility of adsorption sites on PS/SPAC composite fibers. This study showed that most SPAC adsorption sites are still accessible when incorporated into electrospun polymer fibers, regardless of whether the carbon particle size is larger or smaller than the fiber diameter. It can be speculated that the disposition of fine particles on the external surface of PS fibers as well as partial incorporation of large SPAC particles in the fiber allow diffusion of probe molecules onto the ultimate sorption sites of SPAC particles.

Electrospinning Triboelectric Laminates: A Pathway for Scaling Energy Harvesters.

Herein, a new paradigm of triboelectric polymers-the triboelectric laminate-a volumetric material with electromechanical response comparable to the benchmark soft piezoelectric material polyvinylidene difluoride is reported. The electromechanical response in the triboelectric laminate arises from aligned dipoles, generated from the orientation of contact electrification in the laminates bulk volume. The dipoles form between sequential bilayers consisting of two different electrospun polymer fibers of different diameter. The loose interface between the fiber bilayers ensures friction and triboelectric charging between two polymers. The electric output from the electrospun triboelectric laminate increases with increasing density of the bilayers. This system design has clear benefits over other flexible devices for mechanical energy harvesting as it does not require any poling procedures, and the electromechanical response is stable over 24 h of continuous operation. Moreover, the electromechanically responsive electrospun laminate can be made from all types of polymers, thus providing ample room for further improvements or functionalities such as stretchability, biodegradability, or biocompatibility. The concept of a triboelectric laminate can be introduced into existing triboelectric nanogenerator form factors, to dramatically increase charge harvesting of a variety of devices.

Electrospun polymer fibers modified with FK506 for the long-term treatment of acute cardiac allograft rejection in a heart transplantation model.

FK506, a first-line immunosuppressant, is routinely administered orally and intravenously following heart transplantation. However, frequent administration can result in a substantial psychological burden to patients, resulting in non-adherence to medication. The purpose of our study is to overcome the disadvantages of systemic drug administration by developing a polymer-based delivery system that is tunable and biodegradable and that can release highly hydrophobic FK506 over extended periods to treat or prevent acute cardiac allograft rejection. Using an electrospinning method, long-acting microfibers were prepared, and FK506 appeared to be continuously released for up to 14 days based on the in vitro release profiles. After implanting the microfiber subcutaneously into the abdominals of transplanted rats, it was found that the infiltration of T cells and macrophages and the secretion of interleukin-2 (IL-2) and IL-1β were significantly reduced compared with those of the free FK506 groups. More importantly, the mean survival time (MST) of the PCL-FK506 group was significantly extended in comparison with that of untreated control recipients and free FK506 (MST of untreated control recipients, free FK506, and PCL-FK506 was 8, 26.1, and 37, respectively). In conclusion, we propose that this drug delivery approach would be suitable for developing long-lasting immunomodulatory agents that prolong cardiac graft survival safely and effectively.

Engineering dual-stimuli responsive poly(vinyl alcohol) nanofibrous membranes for cancer treatment by magnetic hyperthermia

The development of new cancer treatment options, such as multifunctional devices, allows for a more personalized treatment, avoiding the known severe side effects of conventional options. In this context, on-demand drug delivery systems can actively control the rate of drug release offering a precise control of treatment. Magnetically and thermally controlled drug delivery systems have been explored as on-demand devices to treat chronic diseases and cancer tumors. In the present work, dual-stimuli responsive systems were developed by incorporating Fe3O4 magnetic nanoparticles (NPs) and poly(N-isopropylacrylamide) (PNIPAAm) microgels into electrospun polymeric fibers for application in cancer treatment. First, Fe3O4 NPs with an average diameter of 8 nm were synthesized by chemical precipitation technique and stabilized with dimercaptosuccinic acid (DMSA) or oleic acid (OA). PNIPAAm microgels were synthesized by surfactant-free emulsion polymerization (SFEP). Poly(vinyl alcohol) (PVA) was used as a fiber template originating fibers with an average diameter of 179 ± 14 nm. Stress tests of the membranes showed that incorporating both microgels and Fe3O4 NPs in electrospun fibers increases their Young's modulus. Swelling assays indicate that PVA membranes have a swelling ratio of around 3.4 (g/g) and that the presence of microgels does not affect its swelling ability. However, with the incorporation of Fe3O4 NPs, the swelling ratio of the membranes decreases. Magnetic hyperthermia assays show that a higher concentration of NPs leads to a higher heating ability. The composite membrane with the most promising results is the one incorporated with DMSA-coated NPs, since it shows the highest temperature variation, 5.1 °C. To assess the membranes biocompatibility and ability to promote cell proliferation, indirect and direct contact cell viability assays were performed, as well as cell adhesion assays. Following an extract method viability assay, all membrane designs did not reveal cytotoxic effects on dermal fibroblasts and melanoma cancer cells, after 48 h exposure and support long-term viability. The present work demonstrates the potential of dual-stimuli composite membranes for magnetic hyperthermia and may in the future be used as an alternative cancer treatment particularly in anatomically reachable solid tumors.

Immobilized Bacterial Cells on Electrospun Nanofibers for Crude Oil Spills Treatment and Bioremediation

AbstractImmobilization of biological molecules and cells on nanofibers is widely used in many applications ranging from medical to environmental applications. Immobilization materials provide cells with protection and surface for adhesion which in turn increases their efficiency for a particular application and stability over a longer period. Bioremediation of oil spills has recently become popular since scientists have developed processes that rely on cost‐effectiveness and efficacy in crude oil treatments. For improved and sustainable performance of bioremediation, the system requires the development of cost‐effective carrier substrates which undergo slow biodegradability and present a limited negative impact on the environment. Immobilization of bacteria on electrospun polymeric fibers is a recent research development aided by advances in nanotechnology. This could revolutionize bioremediation, treating the problem of crude oil spill pollution. In this review, we discuss the use of electrospinning to manufacture nanofibers entrapping and encapsulating bacterial cells for effective crude oil spill bioremediation. We go further to explain the recent developments in nanofiber technology with special emphasis on the correlation between method of electrospinning and relevant morphology of the formed fibers.

(Invited) ALD-Based Infiltration and Growth of Inorganic Materials in Polymers

Sequential infiltration synthesis (SIS) has emerged in the past decade as a powerful technique for growth of inorganic materials within polymers through atomic layer deposition (ALD) chemistry. In SIS, ALD precursors diffuse into the polymer and interact with it, leading to inorganic materials growth within the polymer’s free volume. If desired, the polymer can later be removed, yielding polymer-templated inorganic structures. Combining SIS with self-assembled block copolymer (BCP) patterns results in selective growth of inorganic materials within the polar domains of the BCP, making it an attractive method for directed templating of inorganic nanostructures. Thus, SIS opens a pathway for exploiting ALD precision and rich materials library in new 3D morphologies, defined by the polymer.To build SIS design rules and expand SIS’ possibilities, we probed SIS growth and evolution at the atomic scale and explored the role of reversible polymer-precursor interactions in SIS growth through a plethora of methods: in-situ growth analysis (microgravimetry and FTIR), ex-situ high-resolution electron microscopy and extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT) calculations. This knowledge was then applied in fabrication by design of metal oxide fibers, porous particles, and membranes.We fabricated Al2O3 and ZnO nanofibers, nanobelts, and core-shell fibers using designed growth profiles within electrospun polymer fibers. By controlling the organometallic precursors’ diffusion time, simultaneous but spatially controlled growth of Al2O3 and ZnO within the fibers was achieved, leading to the formation of metal oxide core-shell fibers. Self-assembled BCP particles were used to template porous metal oxide particles by selective growth of Al2O3 in the major block of the self-assembled structure. The uniform BCP assembly led to uniporous pores in the metal oxide particles. Finally, we utilized SIS and ALD within and onto BCP membranes for exceptional pore size control and pores’ surface engineering, yielding highly selective filtration membranes.

Ambient Humidity-Induced Phase Separation for Electrospun Fiber Morphology Engineering Toward Piezoelectric Self-Powered Sensing

Electrospun polymeric piezoelectric fibers have a considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent-induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher β phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape-adaptive energy harvesting and self-powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self-powered motion sensing.

Accelerated wound closure rate by hyaluronic acid release from coated PHBV electrospun fiber scaffolds

The enormous potential of electrospun polymer fibers allows for their development in the field of biomaterials for tissue engineering and wound healing. Electrospun fibers based on biodegradable polymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) are an ideal material for the production of a biocompatible cell scaffold supporting wound closure and skin regeneration. The aim of this research was to create a fibrous PHBV scaffold supporting the 3D environment for anchoring and proliferation of keratinocytes. Moreover, hyaluronic acid (HA) has been used as a coating on PHBV fibers to improve the wound closure processes. ATR-FTIR results indicated the presence of HA in the PHBV scaffolds and UV–Vis analysis confirmed the release of HA from the fibers over 24h test. Importantly, this release of HA increase keratinocyte activity as well their proliferation leading to accelerated wound closure rate in the scratch tests. The designed HA-coated PHBV scaffolds demonstrate the great potential of surface-modified electrospun polymer fibers for wound healing.

Electrospun polyvinylidene fluoride mats as a novel platform for dye-doped random lasing

The development of novel polymer nanofiber-based photonic devices has led to improved optical materials, extremely appealing for random lasers (RLs). Recently, electrospun polymer fibers have been proposed as convenient materials for RLs, leading to a versatile, low-cost strategy for developing new scattering materials. Here we utilize electrospun Polyvinylidene fluoride (PVDF) polymer as the system with randomness (scatterers), varying in all directions, and rhodamine 6 g (R6G) as the gain medium. A transition from amplified spontaneous emission to lasing with coherent feedback in dye-doped electrospun polyvinylidene fluoride polymer mats is observed by increasing the gain concentration from 1 mM to 3 mM. Indeed, for 3 mM dye concentration, we can observe the emergence of sharp laser peaks (where peak width narrows down to ≈ 0.2 nm), which are superimposed on the broad emission band. These results made this simple and powerful disordered platform made of R6G doped electrospun PVDF materials as valuable active media for controllable light emission, which is of paramount importance in optical sensing and for versatile microlaser devices.

Electrocrystallization of Calcium Oxalate on Electrospun PCL Fibers Loaded with Phytic Acid as a Template.

Crystallization occurs widely in living organisms where different organs could associate with the calcification process, such as the formation of calcium oxalate (CaOx) calculi in the urinary tract. However, the pathogenesis and the role of an inhibitor in the pathological processes involved in urolithiasis is poorly understood. Therefore, the use of phytic acid (PA) as an inhibitor for the organic fibrillar matrix is a novel approach to inhibit the formation of pathological CaOx crystals. Herein, electrospun polymer fiber meshes of polycaprolactone (PCL) with random (R) and aligned (A) fiber orientations containing PA were prepared by electrospinning, and their role as a 3D organic template in in vitro CaOx crystallization was investigated. CaOx crystals were generated on conductive tin indium oxide (ITO)-modified glass with R-PCL and A-PCL fibers in the presence of PA through an electrocrystallization (EC) procedure. This study provides a simple electrochemical approach to evaluate the role of PA as an inhibitor in the nucleation of pathological CaOx crystals. The resulting CaOx crystals were analyzed by chrono-potentiometry, optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). We found that PA and the fiber orientations are key factors in the nucleation and crystal growth of CaOx, achieving the stabilization of healthy CaOx crystal and the inhibition of the pathological crystal form.

Metallized electrospun polymeric fibers for electrochemical sensors and actuators

Electrospun polymeric fibers present an emerging alternative for the development of flexible electronics, enabling applications in wearable sensors and biosensors for continuous monitoring, and actuators for tissue engineering. The possibility to prepare sub-micrometric polymeric scaffolds, their processing for increasing the conductivity, their modification with different materials, conductive polymers and biomolecules in order to obtain functional flexible electrodes, allows the development of innovative devices for healthcare, and biomedical applications. In this review, the impact of metallized electrospun polymeric fibers in electrochemical (bio)sensors and actuators is discussed. A relation between their structure and functionality is provided, alongside with an overview of the different methods to obtain functional conductive fibers.

Charge transport mechanisms in free-standing devices with electrospun electrodes

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq3/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq3) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 Ω/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10–6 cm2 V−1 s−1 at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole–Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

Tablet Formulations of Polymeric Electrospun Fibers for the Controlled Release of Drugs with pH-Dependent Solubility.

A challenge in the pharmaceutical sector is the development of controlled release dosage forms for oral administration of poorly soluble drugs, in particular, drugs characterized by pH-dependent solubility through the gastrointestinal tract, which itself shows wide variability in terms of environmental pHs. The best approach is to increase the dissolution rate of the drugs at the different pHs and only then modify its release behavior from the pharmaceutical form. This work aims to demonstrate the ability of properly designed polymeric nanofibers in enhancing the release rate of model drugs with different pH-dependent solubility in the different physiological pHs of the gastrointestinal tract. Polymeric nanofibers loaded with meloxicam and carvedilol were prepared using the electrospinning technique and were then included in properly designed tablet formulations to obtain fast or sustained release dosage forms. The nanofibers and the tablets were characterized for their morphological, physico-chemical and dissolution properties. The tablets are able to deliver the dose according to the expected release behavior, and zero-order, first-order, Higuchi, Korsmeyer–Peppas and Hixon–Crowell kinetics models were used to analyze the prevailing release mechanism of the tablets. This study shows that the electrospun fibers can be advantageously included in oral dosage forms to improve their release performances.

Disposable superoxide dismutase biosensors based on gold covered polycaprolactone fibers for the detection of superoxide in cell culture media.

A novel and disposable biosensor based on superoxide dismutase (SOD) immobilized on gold metallized polycaprolactone electrospun polymeric fibers (PCl/Au) has been developed for the determination of superoxide (O2•-) in cell culture media. SOD biosensors were constructed employing three immobilization methods: cross-linking with EDC/NHS at a cysteine self-assembled monolayer (PCl/Au/SODCYS), biopolymer encapsulation with chitosan (PCl/Au/SODCHI) and cross-linking with glutaraldehyde (PCl/Au/SODGA). Scanning electron microscopy was performed at the three different biosensors to evaluate their surface morphologies. Biosensors were employed for the electrochemical detection of superoxide by fixed potential amperometry at different applied potentials, with two distinct enzymatic mechanisms being proposed: i) the reduction of the enzymatically generated peroxide, at -0.3V, for which the PCl/Au/SODCHI biosensor presented the highest value of sensitivity of 40.1μAmM-1cm-2, and ii) the regeneration of the enzyme catalytic copper centre, at +0.3V, for which the PCl/Au/SODCYS biosensor had the highest sensitivity value of 16.1μAmM-1cm-2. The proposed recognition mechanisms were further confirmed by cyclic voltammetric measurements, which enabled also to determine the amount of immobilized electroactive SOD, with highest value corresponding to the PCl/Au/SODCYS biosensor. The biosensors with best analytical performance, PCl/Au/SODCYS and PCl/Au/SODCHI, were further investigated for stability and selectivity, with best results for the PCl/Au/SODCYS, chosen for superoxide monitoring in cell culture media. The study is promising for future application of PCl/Au/SODCYS for the on-line superoxide monitoring of superoxide in cell cultures, grown directly on the biosensor itself.

Ambient Humidity-Induced Phase Separation for Fiber Morphology Engineering toward Piezoelectric Self-Powered Sensing.

Electrospun polymeric piezoelectric fibers have a considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive β phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent-induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher β phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape-adaptive energy harvesting and self-powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self-powered motion sensing.

Shape-Memory Materials via Electrospinning: A Review

This review aims to point out the importance of the synergic effects of two relevant and appealing polymeric issues: electrospun fibers and shape-memory properties. The attention is focused specifically on the design and processing of electrospun polymeric fibers with shape-memory capabilities and their potential application fields. It is shown that this field needs to be explored more from both scientific and industrial points of view; however, very promising results have been obtained up to now in the biomedical field and also as sensors and actuators and in electronics.

Hybrid photonic-plasmonic mode-coupling induced enhancement of the spontaneous emission rate of CdS/CdSe quantum emitters

In this paper, a hybrid photonic-plasmonic resonator, which comprises an electrospun polymer fiber with a micrometer diameter and a core/shell nanostructure with a gold nanoparticle core, is constructed to investigate the dynamics of the coupled spontaneous emission of CdS/CdSe quantum dots (QDs). The gold nanoparticle core; covered with a silica shell, anchored with individual CdS/CdSe QDs, is placed inside a hollow cylindrical nanocavity formed on the surface of the microfiber to enable integration of the optical mode with the plasmonic effect, which is induced by the localized surface plasmons of the metal nanoparticle being present in the vicinity of the dipoles. The spontaneous emission rate of the QDs, coupled into the hybrid photonic-plasmonic mode, is measured to enhance by a factor of 23 via a time-resolved experimental technique. This result suggests that the regeneration of the optical mode-field inside the photonic-plasmonic resonator through the interaction of the dipoles with the localized surface plasmons of a metal nanoparticle strongly enhances the density of the electromagnetic states of the quantum emitters to facilitate an enhanced spontaneous emission within the host medium of the proposed polymer based-photonic structure.

Emerging polymeric electrospun fibers: From structural diversity to application in flexible bioelectronics and tissue engineering.

Electrospinning (e-spin) technique has emerged as a versatile and feasible pathway for constructing diverse polymeric fabric structures, which show potential applications in many biological and biomedical fields. Owing to the advantages of adjustable mechanics, designable structures, versatile surface multi-functionalization, and biomimetic capability to natural tissue, remarkable progress has been made in flexible bioelectronics and tissue engineering for the sensing and therapeutic purposes. In this perspective, we review recent works on design of the hierarchically structured e-spin fibers, as well as, the fabrication strategies from one-dimensional individual fiber (1D) to three-dimensional (3D) fiber arrangements adaptive to specific applications. Then, we focus on the most cutting-edge progress of their applications in flexible bioelectronics and tissue engineering. Finally, we propose future challenges and perspectives for promoting electrospun fiber-based products toward industrialized, intelligent, multifunctional, and safe applications.

Tuneable optical gain and broadband lasing driven in electrospun polymer fibers by high dye concentration

Electrospun polystyrene fibers doped with a blue emitting dye across a broad range of concentration show high and tunable optical gain, reaching broadband lasing action by disordered network configurations.

Highly Aligned Electrospun Polymer Fibers Produced Using a Corrugated Static Collector

Highly Aligned Electrospun Polymer Fibers Produced Using a Corrugated Static Collector