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Abstract
We designed a high-sensitivity magnetic resonance imaging contrast agent that could be used to diagnose diseases. First, magnetic nanocrystals were synthesized by a thermal decomposition method on an organic solvent to obtain a high magnetism and methoxy poly(ethylene glycol)-poly(lactic acid) as an amphiphilic polymer using the ring-opening polymerization method to stably disperse the magnetic nanocrystals in an aqueous phase. Subsequently, the magnetic nanoclusters simultaneously self-assembled with methoxy poly(ethylene glycol)-poly(lactic acid) using the nano-emulsion method to form magnetic nanoclusters. Because their shape was similar to a raspberry, they were named PEGylated magnetic nano-assemblies. The PEGylated magnetic nano-assemblies were dispersed stably in the aqueous phase with a uniform size of approximately 65–70 nm for an extended period (0 days: 68.8 ± 5.1 nm, 33 days: 69.2 ± 2.0 nm, and 44 days: 63.2 ± 5.6). They exhibited both enough of a magnetic resonance (MR) contrast effect and biocompatibility. In an in vivo study, the PEGylated magnetic nano-assemblies provided a high contrast effect for magnetic resonance images for a long time after one treatment, thereby improving the diagnostic visibility of the disease site.
Highlights
Magnetic resonance (MR) imaging is the best investigative tool to obtain tomographic images with a high resolution and to offer excellent anatomical information in living organisms
Magnetic nanocrystals synthesized in an organic phase have well-defined crystallized structures and a high magnetic sensitivity, and they have been reported to be used as contrast agents [4,18,19]
Two main surface modification methods are used for PEG-based materials: (1) the exchange method, in which the hydrophobic ligand on the magnetic nanocrystal (MNC) surface is exchanged with PEG at a high temperature, and (2) the addition method, in which the surface of a hydrophobic MNC is wrapped with the emulsion method using a PEG-based amphiphilic polymer as a surfactant [23–25,27,31–38,40–42]
Summary
Magnetic resonance (MR) imaging is the best investigative tool to obtain tomographic images with a high resolution and to offer excellent anatomical information in living organisms. Magnetic nanocrystals synthesized in an organic phase have well-defined crystallized structures and a high magnetic sensitivity, and they have been reported to be used as contrast agents [4,18,19] Since they are dispersed in the organic phase, additional surface modification with a hydrophilic layer (e.g., polyethylene glycol (PEG)) is required to improve their colloidal stability in the aqueous phase [7,9,10,12,20–22]. Two main surface modification methods are used for PEG-based materials: (1) the exchange method, in which the hydrophobic ligand on the magnetic nanocrystal (MNC) surface is exchanged with PEG at a high temperature, and (2) the addition method, in which the surface of a hydrophobic MNC is wrapped (or coated or covered) with the emulsion method using a PEG-based amphiphilic polymer as a surfactant [23–25,27,31–38,40–42] This addition method enables the fabrication of a multifunctional nanocomposite by simultaneously loading drugs and fluorescent materials as well as MNCs. obtaining uniformly sized nanoparticles, especially nanoclusters, is not easy. The particles are formed by homogeneously aggregating MNCs that are dispersed stably in a water phase and are named PEGylate magnetic nano-assemblies (PEGylated MNs)
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