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Clustering of Iron Oxide Nanoparticles into Poly(ethylene oxide)-block-poly(ε-caprolactone) Nanoassemblies as Ultrasensitive MRI Probes
* 1 , 1 , 1, 2 , 3 , 1, 2 , 1, 2
1  NMR and Molecular Imaging Laboratory, General, Organic and Biomedical Chemistry Department; University of Mons; Belgium
2  Center for Microscopy and Molecular Imaging, Charleroi, Belgium
3  Laboratory of Polymeric and Composite Materials, University of Mons, Belgium


Recently, polymer vesicles called polymersomes have emerged as promising nanocarriers. Several studies have reported the formation of poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) based vesicles due to their high potential for biomedical applications. However, to our knowledge, the incorporation of ultrasmall superparamagnetic iron oxide nanoparticles (USPIO) into these PEO-b-PCL vesicles has not yet been described.

This work reports the self-assemby of PEO2000-b-PCL12650 copolymers with USPIO. PEO2000-b-PCL12650 was chosen as amphiphilic copolymer because PEO block is biocompatible and prolong the circulation time of nanoparticles in vivo whereas PCL block is biodegradable. Moreover, PEO2000-b-PCL12000 copolymers have been reported to form vesicles.

USPIO were synthesized by the thermal decomposition method (magnetic core size of 4.2 nm and 7.5 nm) and self-assembly of PEO2000-b-PCL12650 with USPIO was performed by nanoprecipitation. Polymeric nanoparticles with diameters close to 100 nm and a high USPIO content were formed as shown by dynamic light scattering (DLS), transmission electron microscopy (TEM) and cryo-TEM. These nanoassemblies are characterized by very high r2/r1 ratios (at 20 and 60 MHz) which makes them highly promising canditates as T2-contrast agents for magnetic resonance imaging (MRI). The size of USPIO entrapped in PEO-b-PCL nanoassemblies has a strong impact on their magnetic properties. Indeed it affects both their longitudinal and their transverse relaxivities and thus their magnetic resonance imaging (MRI) sensitivity.

The next steps in further studies will be the incorporation of an anti-cancer drug into these nanocarriers and the attachment of an active targeting group such as an RGD-containing peptide to their surfaces.

Keywords: Superparamagnetic iron oxide nanoparticles, PEO-b-PCL polymers, MRI contrast agents