Showing papers by "Martina Koneracka published in 2006"

Acute toxicity of magnetic nanoparticles in mice.

Abstract: Objectives The acute toxicity of magnetic nanoparticles was effectively lowered by their encapsulation with poly(D,L lactide). In relation to the idea to use magnetic nanoparticles in development of new delivery systems suitable for targeted drug administration, the toxicological profile of five types of magnetic fluids was assessed in mice. Methods The nanoprecipitation method was used to prepare magnetic fluids containing nanoparticles of Fe(3)O(4) encapsulated with biodegradable substances. The acute toxicity testing was performed according to OECD Test Guideline 425. In the pilot distribution study a special staining method was examined for the detection of Fe ions in body tissues of mice after intravenous administration of magnetic fluids. Results The p.o. LD(50) values were greater than 2,000.0 mg/kg of body weight and i.v. LD(50) values were in the range of 231.7-558.9 mg/kg of body weight. Conclusions Of the magnetic nanoparticles tested, those encapsulated with poly(D,L lactide) were the most prospective for further in vivo testing.

Temperature dependence of the critical magnetic field of the structural transition in MBBA-based ferronematics

Abstract: We studied the structural transitions in ferronematics based on the thermotropic nematic liquid crystal MBBA (4′ -methoxybenzylidene-4-n-butylaniline) having a nematic-to-isotropic transition temperature T N–I = 48.0○C and in MBBA-based ferronematics doped with a magnetic suspension consisting of Fe3O4 particles (10 nm in diameter) coated with oleic acid as a surfactant. The ferronematic samples were prepared with different volume concentrations of magnetic particles φ =,1× 10−4, 2× 10−4 and 5×10−4. The temperature dependences of the critical magnetic fields in a bias electric field under strong applied magnetic fields are presented. We calculated the surface density of anchoring energy W at the nematic–magnetic particle boundary. Scaling of the structural transition in the MBBA and MBBA-based ferronematics with the temperature of the nematic-to-isotropic transition was observed.

The DC and AC insulating properties of magnetic fluids based on transformer oil

Abstract: The AC-dielectric breakdown was investigated in magnetic fluids based on transformer oil TECHNOL US 4000 for two orientations of external magnetic field (B ‖ E and B ⊥ E) and in B = 0. The found results were compared with those obtained formerly for the DC-dielectric breakdown. The observations of the time development of the AC-dielectric breakdown showed the presence of partial discharges long before the complete breakdown occurrence, while for DC-dielectric breakdown a complete breakdown of the gap next to the onset of a measurable ionization was characteristic. The comparison of the AC-dielectric breakdown strengths of pure transformer oil and transformer-oil-based magnetic fluid showed better dielectric properties of magnetic fluid in external magnetic field and comparable, but not worse, in B = 0. Regarding to the better heat transfer, provided by magnetic fluids, they could be used in power transformers as insulating fluids. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The study of structural transitions in liquid crystal droplets doped with magnetic particles

Abstract: The magnetically active ferronematic droplets were prepared in solutions of nematic liquid crystal 6CHBT with fme magnetic particles, dissolved in phenyl isocyanate. The phase diagram of the transitions between isotropic, droplet and nematic phases in prepared sample was found. The structural transitions in 6CHBT-based ferronematic and in 6CHBT ferronematic droplets, exposed to external fields, were investigated. The possibility to use the observations of structural transitions for the determination of the type of anchoring of nematic molecules on magnetic particles surfaces was demonstrated.

Some immobilization modes of biologically active substances to fine magnetic particles

Abstract: This paper describes the preparation, characterization and compare of three different modes for coupling biologically active substances to magnetic particles: (i) covalently bound proteins and enzymes to freshly prepared magnetite in the presence of carbodiimide (CDI), (ii) the encapsulation of magnetic nanoparticles and drugs in lipid mixture dipalmitoylphosphatidylcholine (DPPC) and (iii) the encapsulation of magnetic nanoparticles and drugs in biodegradable poly D,L-lactide polymer (PLA).