Oana Marinica

Structure and in vitro biological testing of water-based ferrofluids stabilized by monocarboxylic acids.

Water-based ferrofluids (magnetic fluids) with double-layer steric stabilization by short monocarboxylic acids (lauric and myristic acids) are considered to be a potential source of magnetic nanoparticles in brain cancer (glioblastoma) treatment. Structure characterization in the absence of an external magnetic field is performed, including transmission electron microscopy, magnetization analysis, and small-angle neutron scattering with contrast variation. It is shown that despite the good stability of the systems a significant part of the magnetite nanoparticles are in aggregates, whose inner structure depends on the stabilizer used. In particular, an incomplete coating of magnetite particles is concluded in the case of myristic acid stabilization. The ferrofluids keep their structure unchanged when added to the cancer cell medium. The intracellular accumulations of magnetite from the ferrofluids added to cancer cell cultures as well as its cytotoxicity with respect to human brain cells are investigated.

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.

An innovative synthesis approach toward the preparation of structurally defined multiresponsive polymer (co)networks

A new and facile synthesis approach employed for the fabrication of multiresponsive polymer conetworks characterized by predefined architecture and composition is described for the first time. The presented methodology involves the crosslinking of well-defined 2-(dimethylamino)ethyl methacrylate (DMAEMA) homopolymers and polyDMAEMA-containing diblock and triblock copolymers prepared by Reversible Addition Fragmentation chain Transfer (RAFT) polymerization, using 1,2-bis-(2-iodoethoxy)ethane (BIEE) as a crosslinker. Unlike other controlled polymerization methods used for the synthesis of well-defined polymer structures, herein the crosslinking step is undemanding since no special synthesis requirements are necessary such as heat and inert conditions. Most importantly it enables the encapsulation of inorganic nanoparticulate systems within the 3-dimensional polymer structures, resulting in the generation of polymer-based nanocomposite (co)networks with structurally defined characteristics. More precisely, the BIEE-crosslinking step is carried out in the presence of pre-formed oleic acid coated magnetite (Fe3O4) nanoparticles. The swelling behavior of the resulting (co)networks is investigated in organic and aqueous media at different pHs. Moreover, the magnetic response of the Fe3O4-containing (co)networks is studied by means of vibrational sample magnetometry, demonstrating their superparamagnetic behavior at room temperature. This new approach may be easily expanded to generate structurally defined multiblock (and hence multifunctional) copolymer conetworks and organic–inorganic nanocomposites.

Clustering in Water Based Magnetic Nanofluids: Investigations by Light Scattering Methods

Nanosized magnetite particles, with mean physical diameter of about 7 nm, obtained by chemical coprecipitation procedure were dispersed in water carrier by applying sterical stabilization of particles in order to prevent their aggregation and to ensure colloidal stability of the systems. Different chain length (C12, C14, C18) carboxylic acids (lauric (LA), myristic (MA) and oleic (OA)) were used for double layer coating of magnetite nanoparticles. Structural and magnetic properties were investigated by electron microscopy (TEM), dynamical and static light scattering (DLS, SLS) and magnetometry (VSM) to evaluate the role of chain length and of the saturated/unsaturated nature of surfactant layers. Also investigated were two water based magnetic nanocomposites obtained by encapsulating the magnetic nanoparticles in polymers with different functional properties.

Magnetic nanocomposites obtained using high evaporation rate magnetic nanofluids

In this paper, we study the influence of the addition of small amounts of nanomagnetic fluids in resins, some specific properties of these fluids and the possibility to produce a new category of magnetisable nanocomposite materials. The research was focused on the compatibility between the various types of nanomagnetic fluids and resins. Samples were prepared varying the resins, carrier liquids and volume fraction of magnetic nanoparticles. The polymerisation process of nanocomposites was investigated under the influence of applied magnetic field. Results of investigations presented in this paper refer to the microstructure of the samples (optical and/or electronic microscopy), and to the mechanical properties corresponding to different preparation methods (three points bending test, elastic properties, gel time determination).

Characteristic properties of a magnetic nanofluid used as cooling and insulating medium in a power transformer

Magnetic nanofluids (widely known as ferrofluids or magnetic liquids) have a unique property - they are responsive to the application of a magnetic field, which allows for the possibility of controlling the flow and the convective heat transfer. This paper presents the characteristic thermo-physical, magnetic and dielectric properties of a transformer oil based magnetic nanofluid, specially prepared for use as a cooling and insulating medium in a power transformer.

Synthesis and Characterization of Magnetically Controllable Nanostructures Using Different Polymers

We report a comparative study of hybrid nanostructures prepared by using water based magnetic nanofluids and polymers such as poly(N‐isopropylacrylamide) and pyrrole copolymer functionalized with glycyl‐leucine. Design of magnetic nanostructures could be achieved using different synthesis procedures that allow either coating or clustering the magnetic nanoparticles from magnetic fluid by the addition of polymer. Physical‐chemical characteristics of hybrid magnetic nanostructures were investigated by FTIR, TEM, DLS, rotational viscosimetry and magnetization measurements. Functionalized pyrrole copolymer coated magnetite nanoparticles with mean size around 9 nm have superparamagnetic behavior and saturation magnetization value of 65 emu/g_Fe3O4. Clusters of magnetite nanoparticles from the water based magnetic nanofluid were encapsulated into polymeric PNIPA spheres having diameters in the range 50–100 nm. The procedure applied allowed to achieve high magnetic loading of polymeric microspheres, having satur...

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.

Study of Static Magnetic Properties of Transformer Oil Based Magnetic Fluids for Various Technical Applications Using Demagnetizing Field Correction

Static magnetization data of eight transformer oil based magnetic fluid samples, with saturation magnetization ranging in a large interval from 9 kA/m to 90 kA/m, have been subjected to the demagnetizing field correction. Using the tabulated demagnetization factors and the differential magnetic susceptibility of the samples, the values of the radial magnetometric demagnetization factor were obtained in the particular case of VSM880 magnetometer. It was found that the demagnetizing field correction keeps the saturation magnetization values unchanged, but instead the initial magnetic susceptibility of the magnetic fluid samples varies widely. The mean magnetic diameter, obtained through magnetogranulometry from the measured data, is higher than that obtained from the corrected ones and the variation rate increases with the magnetic particle volume fraction growth.