Ioanna Savva

Fabrication, characterization, and evaluation in drug release properties of magnetoactive poly(ethylene oxide)-poly(L-lactide) electrospun membranes.

The fabrication of electrospun magnetoactive fibrous nanocomposite membranes based on the water-soluble and biocompatible poly(ethylene oxide) (PEO), the biocompatible and biodegradable poly(L-lactide) (PLLA) and preformed oleic acid-coated magnetite nanoparticles (OA.Fe3O4) is reported. Visualization of the membranes by electron microscopy techniques reveals the presence of continuous fibers of approximately 2 μm in diameter, with the magnetic nanoparticles being evenly distributed within the fibers, retaining at the same time their nanosized diameters (≈ 5 nm). Thermal gravimetric analysis measurements suggest that the magnetic nanoparticles embedded within the polymer fibers affect favorably the thermal stability of the membranes. Moreover, assessment of their magnetic characteristics by vibrating sample magnetometry discloses tunable superparamagnetic behavior at ambient temperature. For the first time, the biocompatibility and biodegradability of PEO/PLLA and the tunable magnetic activity of the OA.Fe3O4 are combined in the same drug delivery system, with N-acetyl-p-aminophenol (acetaminophen) as a proof-of-concept pharmaceutical. Furthermore, their heating ability under alternating current (AC) magnetic field conditions is evaluated using frequency of 110 kHz and corresponding magnetic field strength of 25 mT (19.9 kA/m). Consequently, these magnetoactive fibrous nanocomposites exhibit promising characteristics for future exploitation in magnetothermally triggered drug delivery.

Evaluation of electrospun polymer–Fe3O4 nanocomposite mats in malachite green adsorption

Magnetoactive nanocomposite fibers, based on poly(ethylene oxide) (PEO), poly(L-lactide) (PLLA) and pre-formed oleic acid-coated magnetite nanoparticles (OA·Fe3O4), were fabricated by electrospinning and evaluated for the first time as substrates for the adsorption of N-methylated diaminotriphenylmethane dye (malachite green oxalate, MG) from aqueous media. The adsorption of MG onto the fibers was investigated under ambient conditions by means of UV-Vis spectrophotometry as a function of initial dye concentration and solution pH. Equilibrium data for MG adsorption were well-fitted with the Langmuir isotherm model indicating a monolayer adsorption process. The effect of magnetite nanoparticles on the adsorption efficacy has been also demonstrated by performing the aforementioned studies on fibers that did not contain OA·Fe3O4. The obtained results suggested that the presence of embedded magnetite nanoparticles reduces the fiber adsorption efficiency to some extent. Moreover, the thermodynamic parameters determined from adsorption experiments carried out at three different temperatures indicated that the adsorption of MG onto the Fe3O4-free and the Fe3O4-containing fibers is spontaneous and endothermic. Although the presence of Fe3O4 within the fibers disfavored somewhat the adsorption process, nevertheless, the incorporation of the magnetic nanoparticles within these materials assisted their recovery from aqueous solutions by means of an externally applied magnetic field. Desorption of MG from the fibers could be realized upon fiber immersion in alcohol solution, thus allowing the regeneration and re-use of the adsorbents that retained the same adsorption efficiency after multiple regeneration cycles. MG adsorption studies performed in urban wastewater samples by using the PEO/PLLA and the PEO/PLLA/OA·Fe3O4 fibers as adsorbents, demonstrated the potential use of these materials in real wastewater treatment applications.

PVP-crosslinked electrospun membranes with embedded Pd and Cu2O nanoparticles as effective heterogeneous catalytic supports

Palladium(0) (Pd) and copper(I) oxide (Cu2O) nanoparticles (NPs) were successfully embedded in electrospun polyvinylpyrrolidone (PVP) fibrous membranes. The fabrication process involved the synthesis of stable, PVP-capped Pd and Cu2O colloidal hybrid solutions in methanol that on subsequent electrospinning afforded PVP–Pd and PVP–Cu2O fibrous mats. The morphology of the as-prepared nanocomposite fibers was characterised using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM revealed the presence of bead-free, cylindrical fibers with diameters in the submicrometer range while TEM revealed the presence of spherical Pd and Cu2O NPs with diameters below 10 nm that were evenly distributed within the fibers. Thermal treatment of the PVP–Pd and the PVP–Cu2O membranes afforded crosslinked fibrous mats as supported by SEM. Furthermore, the presence of homogeneously distributed Pd and Cu2O NPs within the crosslinked polymer fibers was confirmed by HRTEM/EDX analyses. The above-mentioned nanocomposite fibers demonstrated high catalytic efficacy as heterogeneous catalytic supports in Heck, Suzuki (PVP–Pd) and click (PVP–Cu2O) reactions. Finally, the reusability of the membranes was briefly investigated with up to three consecutive runs being effective.

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

Abstract We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMAx-b-AEMAy/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.

Alignment of electrospun polymer fibers using a concave collector

During recent years, electrospinning has become a powerful technique for the cost-effective production of fibrous materials with diameters ranging from a few nanometers up to a few micrometers. In a conventional electrospinning system the produced fibers are collected on a flat grounded collector in a random manner, resulting in isotropic non-woven fibrous mats. Many researchers have been focusing on the modification of the electrospinning collectors for inducing fiber orientation since aligned fibrous mats exhibit unique mechanical, electrical and optical properties rendering them highly attractive in many fields. Unlike other reported collector modification approaches developed for inducing fiber alignment via electrospinning, a very simple concept for producing aligned polymer fibers is presented herein, based on the modification of the electric field profile by replacing the flat metallic collector employed in a typical electrospinning set-up, with a concave one. The electric field profile developed in the case of the flat and the concave collectors was simulated performing a finite elements analysis. Most importantly electrospun meshes were produced and quantification of fiber alignment with a Fourier transform method on different deposition sites of the concave collector showed an up to 70% fiber alignment in the center area. This work creates new prospects towards the design of static collectors employed in electrospinning that could enable the fabrication of highly aligned electrospun fibers.

Well-defined fluoro- and carbazole-containing diblock copolymers: synthesis, characterization and immobilization onto Au-coated silicon surfaces

A series of well-defined diblock copolymers consisting of 2-(N-carbazolyl)ethyl methacrylate (CbzEMA) and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (HFBMA) (CbzEMAx-b-HFBMAy) was synthesized by Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization. All polymers were characterized in terms of molecular weights, molecular weight distributions and chemical compositions using Size Exclusion Chromatography (SEC), Fourier Transform Infrared (FTIR) spectroscopy and Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy, respectively. The thermal properties (glass transition and decomposition temperatures) of the CbzEMAx and HFBMAx homopolymers and the CbzEMAx-b-HFBMAy diblock copolymers were determined by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). As demonstrated by photoluminescence measurements, immobilization of the dithioester-ended functionalized CbzEMAx-b-HFBMAy chains onto Au-coated silicon surfaces has been accomplished via anchoring of the sulfur-containing end-groups onto the Au surfaces. The presence of the low-surface energy fluorinated block, combined with the electro-active carbazole-containing segment within CbzEMAx-b-HFBMAy diblock copolymers imparts to these immobilized thin layers useful properties towards their potential applicability in gas sensing technologies.

Evaluation of PVP/Au Nanocomposite Fibers as Heterogeneous Catalysts in Indole Synthesis.

Electrospun nanocomposite fibers consisting of crosslinked polyvinylpyrrolidone (PVP) chains and gold nanoparticles (Au NPs) were fabricated, starting from highly stable PVP/Au NP colloidal solutions with different NP loadings, followed by thermal treatment. Information on the morphological characteristics of the fibers and of the embedded Au NPs was obtained by electron microscopy. Cylindrical, bead-free fibers were visualized by Scanning Electron Microscopy (SEM) while Transmission Electron Microscopy (TEM) and Energy Diffraction X-ray (EDX) analysis supported the presence of Au NPs within the fibers and gave information on their morphologies and average diameters. These materials were briefly evaluated as heterogeneous catalytic supports for the gold-catalyzed intramolecular cyclisation of 2‑(phenylethynyl)aniline to form 2-phenyl-1H-indole. The performance of the gold catalyst was strongly dependent on the Au NP size, with the system containing the smallest Au NPs being the more effective. Moreover, a slight drop of their catalytic efficiency was observed after three consecutive reaction runs, which was attributed to morphological changes as a consequence of fiber merging.

Uranium(VI) binding by pine needles prior and after chemical modification

Adsorption of U(VI) by pine needles prior and after carbonization and following oxidation has been investigated by batch-type experiments and characterized by FTIR and SEM measurements. The experimental data have been fitted by the Langmuir adsorption isotherm and the highest adsorption efficiency was observed for the carbonized and surface oxidized material, followed by the non-treated pine needles and the carbonized material. The highest U(VI) adsorption observed after surface oxidation of the carbonized material is attributed to the presence of carboxylic moieties, which possess increased affinity for the U(VI) cations and form inner-sphere surface complexes.

Fabrication and Bioapplications of Magnetically Modified Chitosan-based Electrospun Nanofibers

Abstract The fabrication of magnetically modified electrospun nanocomposite fibers based on a naturally-derived biocompatible and biodegradable polysaccharide chitosan (CS) and the hydrophilic and biocompatible poly(vinylpyrrolidone) (PVP) is reported herein. The anchoring of magnetic nanoparticles (MNPs) onto the surfaces of the electrospun PVP/CS fibers was carried out by a post-magnetization process based on chemical coprecipitation, via immersing the produced fibrous mats in an aqueous solution containing Fe(II) and Fe(III) salts at appropriate molar ratios, followed by the addition of a weak base to yield MNPs. Electron microscopy revealed the presence of continuous micron and submicron fibers surface-decorated with MNPs. The magnetically modified PVP/CS fibers exhibited superparamagnetic behavior at ambient temperature. The magnetic fibrous nanocomposite carrier was employed for the immobilization of Saccharomyces cerevisiae cells and their use for sucrose hydrolysis, and Candida rugosa lipase and its use for artificial substrate hydrolysis.