Optimized synthesis of 100 nm diameter magnetoliposomes with high content of maghemite particles and high MRI effect.

Magnetoliposomes are liposomes surrounding an iron oxide core, which are used as contrast enhancing agents in magnetic resonance imaging (MRI). One method for producing magnetoliposomes consists of hydration of a lipid film with citrate-coated iron oxide particles followed by extrusion. Two parameters are of major importance for in vivo applications of magnetoliposomes, namely their size, which must be small, optimally around 100 nm diameter, in order to ensure their prolonged circulation in the bloodstream, and their iron content, which must be maximal for generating high MRI effect. We studied the formation of magnetoliposomes by passive encapsulation of maghemite (γ-Fe2O3) particle suspensions of varying concentrations, with the objective of producing magnetoliposomes of small size and high iron content. The iron to lipid ratio was used to determine the iron content of the magnetoliposomes after the successive purification steps and cryo-TEM was used to characterize their size, their homogeneity and the efficiency of purification. The size of citrate-coated maghemite clusters was found to be of critical importance for obtaining magnetoliposomes smaller than 200 nm. We were able to reproducibly synthesize magnetoliposomes of 100 nm diameter with high iron content –up to 77 particles per liposome (5.6 moles iron per mole lipid) – and high r2 MRI relaxivity – up to 320 m m−1 . s−1. The magnetoliposomes present improved characteristics compared with previous reports. Future research will focus on using these magnetoliposomes as drug delivery systems for in vivo diagnostics or therapeutics applications. Copyright © 2011 John Wiley & Sons, Ltd.