Preparation and characterization of lipid vesicles entrapping iron oxide nanoparticles

Nanometric assemblies, activated and controlled through external stimuli, represent an innovative stage in the development of multifunctional therapeutics. In particular, magnetite nanoparticles embedded in liposomes represent submicrometric carriers that can be activated by external magnetic fields, showing high efficacy in reaching tumor cells offering new exciting opportunities towards the development of active targeting systems. Actually, synthesis and characterization of such nanoscale carriers, as well as the assessment of their entrapment capacity, is of great interest for the scientific community. We report here the formation and the characterization of magnetoliposomes (MLs): phospholipid vesicles encapsulating magnetite nanoparticles. MLs were prepared by embedding hydrophilic nanoparticles of commercially available carboxymethyl-dextran coated superparamagnetic iron oxide particles inside the vesicles at different lipid/nanoparticles ratios. Liposomes were prepared by the thin lipid film hydration method: a fixed amount of lipids was dissolved in organic solvent and the obtained solution was evaporated until dryness. Then the dry lipid film was hydrated with a buffered aqueous solution of different concentrations of carboxymethyl-dextran coated magnetite. The resulting MLs, heterogeneous in their size, were extruded through polycarbonate membranes to obtain homogeneous size of unilamellar vesicles. Size exclusion chromatography was used to remove non-entrapped nanoparticles. Magnetite content was determined by 1,10-phenanthroline (Kiwada assay) and Belikov methods and also by flame absorption spectrometry. Physical characterization was performed by dynamic light scattering to determine the mean particles diameter, the size distribution, and the ζ-potential. Physical stability of MLs stored at 4 °C was investigated up to 4 weeks to assess the effect on time of the entrapment of the nanoparticles within the liposomes. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.