Controlled Clustering of Superparamagnetic Nanoparticles Using Block Copolymers: Design of New Contrast Agents for Magnetic Resonance Imaging

Abstract

When polyelectrolyte-neutral block copolymers are mixed in aqueous solutions with oppositely charged species, stable complexes are found to form spontaneously. The mechanism is based on electrostatics and on the compensation between the opposite charges. Electrostatic complexes exhibit a core-shell microstructure. In the core, the polyelectrolyte blocks and the oppositely charged species are tightly bound and form a dense coacervate microphase. The shell is made of the neutral chains and surrounds the core. In this paper, we report on the structural and magnetic properties of such complexes made from 6.3 nm diameter superparamagnetic nanoparticles (maghemite gamma-Fe(2)O(3)) and cationic-neutral copolymers. The copolymers investigated are poly(trimethylammonium ethylacrylate methyl sulfate)-b-poly(acrylamide), with molecular weights 5000-b-30000 g mol(-)(1) and 110000-b-30000 g mol(-)(1). The mixed copolymer-nanoparticle aggregates were characterized by a combination of light scattering and cryo-transmission electron microscopy. Their hydrodynamic diameters were found in the range 70-150 nm, and their aggregation numbers (number of nanoparticles per aggregate) from tens to hundreds. In addition, Magnetic Resonance Spin-Echo measurements show that the complexes have a better contrast in Magnetic Resonance Imaging than single nanoparticles and that these complexes could be used for biomedical applications.

Tumor pH-responsive flower-like micelles of poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(l-histidine)

“…In tumor treatment the micelles system has proven effective in regression of tumor size while minimizing damage to the healthy tissues [4] and is being actively investigated in conjunction with hyperthermia [5], ultrasound [6], specific enzyme-induced cleavable bonds [7][8][9], and specific ligands or antibodies [10][11][12][13] for active targeting purposes.…”

Influence of Explicit Ions on Titration Curves and Conformations of Flexible Polyelectrolytes: A Monte Carlo Study

“…[1][2][3][4][5][6] The range of parameters influencing polyelectrolyte conformation, chemical reactivity, and complexation processes is not completely understood and continues to stimulate intensive research in this field because they control directly many industrial [7][8][9][10] and biological processes. [11][12][13][14] The particular physicochemical properties of polyelectrolyte chains arise from the long-range nature of the Coulomb interactions.…”

Preparation and control of the formation of single core and clustered nanoparticles for biomedical applications using a versatile amphiphilic diblock copolymer

“…It is important to stress that both single core and clustered IONPs were prepared with the same coating polymer, which has not been previously reported, to the best of our knowledge. Some recent reports have shown that the MRI contrast, e.g., the signal drop with T 2 weighted imaging, can be significantly enhanced by clustered IONPs [12,[27][28][29][30]. However, the samples of single or clustered IONPs employed were coated with different materials which may have affected their magnetic properties [12,28,31].…”

“…Some recent reports have shown that the MRI contrast, e.g., the signal drop with T 2 weighted imaging, can be significantly enhanced by clustered IONPs [12,[27][28][29][30]. However, the samples of single or clustered IONPs employed were coated with different materials which may have affected their magnetic properties [12,28,31]. Our measurements of transverse T 2 relaxation times showed that the clustered IONPs exhibit an approximate 3.7-fold increase in the transverse relaxation rate R 2 (1/T 2 , s -1 ) when compared to that of single core IONPs coated with the same copolymer, providing higher MRI contrast at the same Fe concentration (Fig.…”