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Diblock‐Copolymer‐Mediated Self‐Assembly of Protein‐Stabilized Iron Oxide Nanoparticle Clusters for Magnetic Resonance Imaging
Authors:Sari Tähkä  Dr Ari Laiho  Prof Mauri A Kostiainen
Institution:1. Molecular Materials, Department of Applied Physics, Aalto University, 00076 Aalto (Finland);2. AMI Centre, Aalto NeuroImaging, School of Science, Aalto University, 00076 Aalto (Finland);3. Biohybrid Materials, Department of Biotechnology and Chemical Technology, Aalto University, 00076 Aalto (Finland)
Abstract:Superparamagnetic iron oxide nanoparticles (SPIONs) can be used as efficient transverse relaxivity (T2) contrast agents in magnetic resonance imaging (MRI). Organizing small (D<10 nm) SPIONs into large assemblies can considerably enhance their relaxivity. However, this assembly process is difficult to control and can easily result in unwanted aggregation and precipitation, which might further lead to lower contrast agent performance. Herein, we present highly stable protein–polymer double‐stabilized SPIONs for improving contrast in MRI. We used a cationic–neutral double hydrophilic poly(N‐methyl‐2‐vinyl pyridinium iodide‐block‐poly(ethylene oxide) diblock copolymer (P2QVP‐b‐PEO) to mediate the self‐assembly of protein‐cage‐encapsulated iron oxide (γ‐Fe2O3) nanoparticles (magnetoferritin) into stable PEO‐coated clusters. This approach relies on electrostatic interactions between the cationic N‐methyl‐2‐vinylpyridinium iodide block and magnetoferritin protein cage surface (pI≈4.5) to form a dense core, whereas the neutral ethylene oxide block provides a stabilizing biocompatible shell. Formation of the complexes was studied in aqueous solvent medium with dynamic light scattering (DLS) and cryogenic transmission electron microcopy (cryo‐TEM). DLS results indicated that the hydrodynamic diameter (Dh) of the clusters is approximately 200 nm, and cryo‐TEM showed that the clusters have an anisotropic stringlike morphology. MRI studies showed that in the clusters the longitudinal relaxivity (r1) is decreased and the transverse relaxivity (r2) is increased relative to free magnetoferritin (MF), thus indicating that clusters can provide considerable contrast enhancement.
Keywords:block copolymers  iron  magnetic resonance imaging  nanoparticles  self‐assembly
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