Synthesis and characterization of PVP-functionalized superparamagnetic Fe3O4 nanoparticles as an MRI contrast agent

Abstract

Abstract. The magnetite (Fe3O4) nanoparticles (MNPs) coated with poly(N-vinyl pyrrolidone) (PVP) via covalent bonds were prepared as T2 contrast agent for magnetic resonance imaging (MRI). The surface of MNPs was first coated with 3-(trimethoxysilyl) propyl methacrylate (silan A) by a silanization reaction to introduce reactive vinyl groups onto the surface, then poly(N-vinyl pyrrolidone) was grafted onto the surface of modified-MNPs via surface-initiated radical polymerization. The obtained nanoparticles were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), TEM (transmission electron microscopy), VSM (vibrating sample magnetometer), and TGA (thermogravimetric analysis). The MNPs had an average size of 14 nm and exhibited superparamagnetism and high saturation magnetization at room temperature. T2-weighted MRI images of PVP-grafted MNPs showed that the magnetic resonance signal is enhanced significantly with increasing nanoparticle concentration in water. The r1 and r2 values per millimole Fe, and r2/r1 value of the PVP-grafted MNPs were calculated to be 2.6 , 72.1, and 28.1(mmol/l) -1 ·s -1 , respectively. These results indicate that the PVP-grafted MNPs have great potential for application in MRI as a T2 contrast agent. Vol.4, No.6 (2010) 329-338 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2010.42 region that they are accumulated, and hence cause negative contrast and provide a dark state in the image where the compounds are accumulated [15]. However, the direct use of magnetic nanoparticles as in vivo MRI contrast agent results in biofouling of the particles in blood plasma and formation of aggregates that are quickly sequestered by cells of the reticular endothelial system (RES) such as macrophages [16,17]. Furthermore, aggregated nanoparticles change their superparamagnetic response [7]. Therefore, in order to minimize biofouling and aggregation of particles and escape from the RES for longer circulation times, the nanoparticles are usually coated with a layer of hydrophilic and biocompatible polymer such as dextran [18], dendrimers [19], poly(ethylene glycol) (PEG) [20], and poly(vinyl pyrrolidone) (PVP) [21][22][23]. Of synthetic polymers, PVP is water-soluble, non-charged, non-toxic, and is used in various medical applications [24]. While there is a potential concern about covalent interaction between hydrophilic polymers and magnetic nanoparticles in order to increase their stability in physiological medium [25][26][27][28][29], PVP coating on Fe 3 O 4 nanoparticles in all previous works has been achieved through noncovalent interaction. Now, polymers grafting of magnetic nanoparticles is one of the most attractive methods of surface modification [30,31]. In the present study, we carried out chemical synthesis and characterization of PVP-functionalized magnetite (Fe 3 O 4 ) nanoparticles. Since the PVP was bonded to the surface of magnetite nanoparticles through covalent bonds, the prepared magnetic fluid (ferrofluid) was ve...

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