Ladislau Vekas

Application orientated researches on magnetic fluids

Abstract A synthesis is given on the results concerning the preparation methods and properties of several nonpolar and polar magnetic fluids, as well as on their applications in seals, journal bearings, magnetogravimetric separators, transducers and biological experiments.

Magnetic iron oxide nanoparticles: Recent trends in design and synthesis of magnetoresponsive nanosystems.

Recent developments in nanotechnology and application of magnetic nanoparticles, in particular in magnetic iron oxide nanosystems, offer exciting possibilities for nanomedicine. Facile and precise synthesis procedures, high magnetic response, tunable morphologies and multiple bio-functionalities of single- and multi-core magnetic particles designed for nanomedicine applications are thoroughly appraised. This review focuses on the structural and magnetic characterization of the cores, the synthesis of single- and multicore iron oxide NPs, especially the design of the latter, as well as their protection, stabilization and functionalization by desired coating in order to protect against the corrosion of core, to prevent non-specific protein adsorption and particle aggregation in biological media, and to provide binding sites for targeting and therapeutic agents.

Investigations of a magnetorheological fluid damper

This paper presents the results of a study of a magnetorheological fluid (MRF) damper. The principle could be used for such applications as seismic protectors for civil structure (where the dimensions are chosen to handle the greatest forces) or shock absorbers for the automotive industry (where the dimensions are chosen to accommodate heating effects). We describe the preparation method and some characteristics of the MRF, the experimental method (we used a hydraulic linear motor and pressure measurements), and the main experimental results. The external force required to move the damper increases several times when the magnetic field is applied.

Superparamagnetic Hybrid Micelles, Based on Iron Oxide Nanoparticles and Well-Defined Diblock Copolymers Possessing β-Ketoester Functionalities

The quality of surface coating of magnetic nanoparticles destined as nanoprobes in clinical applications is of utmost significance for their colloidal stability and biocompatibility. A novel approach for the fabrication of such a coating involves the synthesis of well-defined diblock copolymers based on 2-(acetoacetoxy)ethyl methacrylate (chelating) and poly(ethylene glycol)methyl ether methacrylate (water-soluble, thermoresponsive), prepared by reversible addition-fragmentation chain transfer polymerization. Fabrication of magneto-responsive micelles was accomplished via chemical coprecipitation of Fe(III)/Fe(II) in the presence of diblock copolymers. Further to the characterization of micellar morphologies, optical and thermal properties, assessment of magnetic characteristics disclosed superparamagnetic behavior. The hybrid micelles did not compromise cell viability in cultures, while in vitro uptake by macrophage cells was significantly lower in comparison to that of the clinically applicable contrast agent Resovist, suggesting that these systems can evade rapid uptake by the reticuloendothelial system and be useful agents for in vivo applications.

Multiresponsive polymer conetworks capable of responding to changes in pH, temperature, and magnetic field: synthesis, characterization, and evaluation of their ability for controlled uptake and release of solutes.

This study deals with the preparation of novel multiresponsive (magnetoresponsive, thermoresponsive and pH-responsive) nanocomposite conetworks consisting of oleic acid-coated magnetite nanoparticles (OA·Fe(3)O(4)), hydrophilic/thermoresponsive hexa(ethylene glycol) methyl ether methacrylate (HEGMA), hydrophobic/metal binding 2-(acetoacetoxy)ethyl methacrylate (AEMA), and pH-responsive/thermoresponsive N-diethylaminoethyl methacrylate (DEAEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) moieties. Conventional free radical copolymerization was employed for the synthesis of random conetworks in the absence and presence of preformed OA·Fe(3)O(4). Further, in characterization of these materials in regards to their swelling behavior in organic and aqueous solvents, thermal/thermoresponsive properties, and composition, assessment of their magnetic characteristics disclosed tunable superparamagnetic behavior. These systems were also evaluated toward their ability to adsorb and release a solute (benzoic acid) in a controlled manner upon varying the pH.

Ferrofluids and Magnetorheological Fluids

Composition, synthesis and structural properties of ferrofluids and magnetorheological fluids are reviewed and compared. The similarities and main differences between the two types of magnetically controllable fluids are outlined and exemplified in the paper. Chemical synthesis and structural characterization of magnetizable fluids for engineering and biomedical applications are thoroughly discussed.

Comparative structure analysis of non-polar organic ferrofluids stabilized by saturated mono-carboxylic acids

The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids.

The antitumor effect of locoregional magnetic cobalt ferrite in dog mammary adenocarcinoma

The endocytosis of nanosized magnetic particles by tumor cells led to numerous tests to establish the use of this phenomenon in antitumor therapy. The direct antitumor effect of a biocompatible cobalt-ferrite-based magnetic fluid directly inoculated in bitch mammary tumors was studied. A direct correlation between tumor cell lysis and cobalt ferrite was established in tumors. Massive endocytosis of magnetic particles was observed 1 h after the contact of magnetic fluid with tumor cells.

Magnetic fluid flow meter for gases

The paper presents the constructive details and functioning principle of an electronic volumetric flow meter for gases, which exploits the properties of magnetic fluids and has no moving mechanical components. It is a bidirectional flow meter, operating both in static and in moving conditions. The flow meter has a sensing unit, which consists of two sensors, one for differential pressure and an other for acceleration or inclination angle and of a tubular measuring element, as well as an electronic measuring system. Details are given an the hydrodynamic-electronic correction mechanism, which eliminates the influences of inclinations and accelerations on the volumic flow signal, followed by a description of the main features of the electronic system. The experiments performed showed the possibility of metering even very small gas volumes, such as 0.1 cm/sup 3/ at a flow rate of 50 cm/sup 3//min. The metering at higher flow rate values, up to 100 m/sup 3//h, needed only the insert of the measuring element corresponding to the requested flow rate domain. >

Magnetite Nanoparticles Stabilized Under Physiological Conditions for Biomedical Application

The biomedical application of water based magnetic fluids (MFs) is of great practical importance. Their colloidal stability under physiological conditions (blood pH ∼ 7.2–7.4 and salt concentration ∼0.15 M) and more in high magnetic field gradient is crucial. Magnetite or maghemite nanoparticles are used in general. In the present work, magnetite nanoparticles were stabilized with different compounds (citric acid (CA) and phosphate) and sodium oleate (NaO) as the most used surfactant in the stabilization of MFs. The adsorption and overcharging effect were quantified, and the enhancement in salt tolerance of stabilized systems was studied. Adsorption, electrophoretic mobility and dynamic light scattering (DLS) measurements were performed. The electrolyte tolerance was tested in coagulation kinetic measurements. Above the adsorption saturation, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The aim was to research these two important effects and demonstrate that none of them alone is enough. The phosphate was not able to stabilize the ferrofluid in spite of our expectation, but the other two additives proved to be effective stabilizing agents. The magnetite was well stabilized by the surface complexation of CA above pH ∼ 5, however, the salt tolerance of citrate stabilized MFs remained much below the concentration of physiological salt solution, and more the dissolution of magnetite nanocrystals was enhanced due to Fe-CA complexation in aqueous medium, which may cause problems in vivo. The oleate double layers were able to stabilize magnetite nanoparticles perfectly at pH ∼ 6 preventing particle aggregation effectively even in physiological salt solution.