ABSTRACT
Core-shell nanoparticles consisting of La(0.75)Sr(0.25)MnO(3) cores covered by silica were synthesized by a procedure consisting of several steps, including the sol-gel method in the presence of citric acid and ethylene glycol, thermal and mechanical treatment, encapsulation employing tetraethoxysilane and final separation by centrifugation in order to get the required size fraction. Morphological studies revealed well-separated particles that form a stable water suspension. Magnetic studies include magnetization measurements and investigation of the ferromagnetic-superparamagnetic-paramagnetic transition. Magnetic heating experiments in 'calorimetric mode' were used to determine the heating efficiency of the particles in water suspension and further employed for biological studies of extracellular and intracellular effects analysed by tests of viability.
Subject(s)
Hyperthermia, Induced/methods , Metal Nanoparticles/therapeutic use , Animals , Colloids , Fluorescein , Fluorescent Dyes , Hyperthermia, Induced/instrumentation , In Vitro Techniques , Lanthanum , Magnetic Field Therapy/instrumentation , Magnetic Field Therapy/methods , Magnetics , Manganese Compounds , Mesenchymal Stem Cells/physiology , Mesenchymal Stem Cells/ultrastructure , Metal Nanoparticles/chemistry , Metal Nanoparticles/ultrastructure , Microscopy, Electron, Transmission , Oxides , Particle Size , Rats , StrontiumABSTRACT
Nanoparticles of manganese perovskite of the composition La(0.75)Sr(0.25)MnO(3) uniformly coated with silica were prepared by encapsulation of the magnetic cores (mean crystallite size 24 nm) using tetraethoxysilane followed by fractionation. The resulting hybrid particles form a stable suspension in an aqueous environment at physiological pH and possess a narrow hydrodynamic size distribution. Both calorimetric heating experiments and direct measurements of hysteresis loops in the alternating field revealed high specific power losses, further enhanced by the encapsulation procedure in the case of the coated particles. The corresponding results are discussed on the basis of complex characterization of the particles and especially detailed magnetic measurements. Moreover, the Curie temperature (335 K) of the selected magnetic cores resolves the risk of local overheating during hyperthermia treatment.
Subject(s)
Calcium Compounds/chemistry , Hyperthermia, Induced/methods , Manganese/chemistry , Nanoparticles/chemistry , Oxides/chemistry , Silicon Dioxide/chemistry , Titanium/chemistry , Calorimetry , Electromagnetic Fields , Hydrogen-Ion Concentration , Materials Testing/methods , Microscopy, Electron, Transmission , Nanoparticles/ultrastructure , Particle Size , Spectrophotometry, InfraredABSTRACT
Composite nanoparticles with variable ratios of M-type Sr-hexaferrite and maghemite phases were prepared via the sol-gel method employing polyvinylalcohol as the stabilizing agent, followed by thermal treatment at 600 °C for 32-190 min. The measurements in static magnetic field revealed considerable variation of the coercivity and remanence depending on the relative content of the highly magnetically anisotropic Sr-hexaferrite phase. Calorimetric heating experiments were carried out on aqueous gel suspensions under an alternating magnetic field of maximum amplitude H(max) = 15.1-68.4 kA m(-1) and frequency ν = 108 kHz. They showed a strong dependence of the heating efficiency on the coercivity and remanence of the composites, with a specific absorption rate (SAR) value ranging from units to tens of W/g(Fe(ferrimagnetic)).
