Preparation and characterization of extruded magnetoliposomes

Phospholipid vesicles encapsulating magnetic nanoparticles (here after called magnetoliposomes) have been prepared for targeting a drug to a specific organ using a magnetic force, as well as for local hyperthermia therapy. Magnetoliposomes are also an ideal platform for use as contrast agents. We describe the preparation and characterization of liposomes containing magnetite, a ferrimagnetic material. These liposomes were obtained by extrusion. To prevent the aggregation of particles, the magnetite was treated--prior to encapsulation--with a surfactant, resulting in a stable ferrofluid suspension. Once the ferrofluid had been obtained, it was used to hydrate the phospholipid layers. Magnetoliposomes had a diameter of around 200 nm, the same pore size as the membranes used for the extrusion. The encapsulation efficiency was dependent on the initial amount of ferrofluid present at the encapsulation stage, and in the worst case was 19%. This value corresponded to 82.06 mmol of magnetite per mole of phospholipid. Although we have used a determined membrane pore to obtain the magnetoliposomes, the method described here allows to prepare magnetoliposomes of different sizes as well as of different magnetite content.