Elaboration of PLLA-based superparamagnetic nanoparticles:: Characterization, magnetic behaviour study and in vitro relaxivity evaluation

Oleic acid-coated magnetite has been encapsulated in biocompatible magnetic nanoparticles (MNP) by a simple emulsion evaporation method. The different parameters influencing the particles size were studied. Between these parameters, the stirring speed and the polymer concentration were found to influence positively or negatively, respectively, the MNP size which varied between 320 and 1500 nm. The magnetite encapsulation efficacy was about than 90% yielding a high magnetite loading of up to 30% (w/w). X-ray diffraction showed that magnetite crystalline pattern was not modified after emulsification and solvent evaporation. The X-ray photoelectron spectroscopy (XPS) results indicated the presence of less than 0.1% of iron atoms at the nanoparticles surface. Vibration simple magnetometer (VSM) showed a superparamagnetic behaviour of the MNP and a saturation magnetization increasing with the increased magnetite amount used in formulation. Moreover, T-1 and T-2 relaxivities of MNP (4.7 T, 20 degrees C) were 1.7 +/- 0.1 and 228.3 +/- 13.1 s(-1) mM(-1), respectively, rendering them in the same category of known negative contrast agents which shorten the T-2 relaxation time. Therefore, by using an appropriate anticancer drug in their formulation, these magnetic nanoparticles can present a promising mean for simultaneous tumor imaging, drug delivery and real time monitoring of therapeutic effect. (c) 2007 Elsevier B.V. All rights reserved.