In situ self-assembly of amphiphilic dextran micelles and superparamagnetic iron oxide nanoparticle-loading as magnetic resonance imaging contrast agents

Abstract

Polymeric micelles have long been considered as promising nanocarrier for hydrophobic drugs and imaging probes, due to their nanoscale particle size, biocompatibility and ability to loading reasonable amount of cargoes. Herein, a facile method for dextran micelles preparation was developed and their performance as carriers of superparamagnetic iron oxide (SPIO) nanocrystals was evaluated. Amphiphilic dextran (Dex-g-OA) was synthesized via the Schiff base reactions between oxidized dextran and oleylamine, and self-assembled in situ into nano-size micelles in the reaction systems. The self-assembling behaviors of the amphiphilic dextran were identified using fluorescence resonance energy transfer technique by detection the energy transfer signal between the fluorophore pairs, Cy5 and Cy5.5. Hydrophobic SPIO nanoparticles (Fe₃O₄ NPs) were successfully loaded into the dextran micelles via the in situ self-assembly process, leading to a series of Fe₃O₄ NPs-loaded micelle nanocomposites (Fe₃O₄@Dex-g-OA) with good biocompatibility, superparamagnetism and strongly enhanced T₂ relaxivity. At the magnetic field of 0.5 T, the Fe₃O₄@Dex-g-OA nanocomposite with particle size of 116.2 ± 53.7 nm presented a higher T₂ relaxivity of 327.9 ${\text{mM}}_{\text{Fe}}^{-1}$·s⁻¹. The prepared magnetic nanocomposites hold the promise to be used as contrast agents in magnetic resonance imaging.