Magnetic colloidal superparticles of Co, Mn and Ni ferrite featured with comb-type and/or linear amphiphilic polyelectrolytes; NMR and MRI relaxometry

Abstract

The ability to encapsulate hydrophobic ferrites in colloidal superparticle structures of an a-telechelic hexadecyl-functionalized poly(methacrylic acid) (C16H33-PMAA) polymer with a linear architecture was investigated and compared with that of two amphiphilic comb-type water-soluble copolymers, namely, P(ANa-co-DAAm) and P(MANa-co-DMA), which are comprised of a poly(sodium acrylate) or poly(sodium methacrylate) backbone and pendent dodecyl acrylamide or dodecyl methacrylate chains, respectively. In the case of C16H33-PMAA, the pH-sensitive self-assembly behavior, which was studied through Nile Red probing and TEM, was related to its encapsulation properties. Hydrophobic MFe2O4 nanoparticles coated with oleylamine (MFe2O4@OAm MNPs, where M = Co, Mn, Ni) with a similar shape and size (∼9 nm) and magnetization values of 87.4, 63.1 and 55.0 emu g(-1) for CoFe2O4@OAm, MnFe2O4@OAm and NiFe2O4@OAm, respectively, were successfully encapsulated into the hydrophobic cores of spherical micellar structures formed by the copolymers in an aqueous solution through a solvent mixing procedure. The synthesized magnetic colloidal superparticles fell in the static dephasing regime (SDR). NMR relaxivity measurements of MFe2O4@P(ANa-co-DAAm), MFe2O4@P(MANa-co-DMA) and MFe2O4@C16H33-PMAA at pH = 4.5 and pH = 7 (where M = Co, Mn, Ni) at 11.7 T were recorded and the transverse relaxivity (r2) (mM(-1) s(-1)) was determined. Among all, the CoFe2O4@polymers demonstrated the highest r2 relaxivity values, ranging from 61.6 for CoFe2O4@C16H33-PMAA (pH = 7) to 316.0 mM(-1) s(-1) for CoFe2O4@P(ANa-co-DAAm). The relaxation efficiency (r1 and r2) of CoFe2O4@P(ANa-co-DAAm) was investigated further by magnetic resonance imaging (MRI) at 1.5 T and 3 T and the r2/r1 ratios were found to be 16.5 and 18.2, respectively, indicating its potential use as a T2 contrast agent.

Magnetic hyperthermia efficiency and MRI contrast sensitivity of colloidal soft/hard ferrite nanoclusters

“…Moreover, the difference between MnNCs and Mn@CoNCs stems from the different size of clusters (75 and 81 nm, respectively). Both clusters due to their size belong to the so-called motional average regime (MAR) where relaxivities increases in respect to the nanocluster diameter [46], as also indicated by us before [47].…”

Investigation of Specific Targeting of Triptorelin-Conjugated Dextran-Coated Magnetite Nanoparticles as a Targeted Probe in GnRH+ Cancer Cells in MRI

“…Such small size could be related to the size of single crystal while TEM images revealed the particle dimension. However, slightly higher sizes could be optimal for the enhancement of the r 2 relaxivity [ 35 , 36 ]. In addition, the small-sized SPIONs increased the surface-to-volume ratio, and thus the increased dead layer component decreased magnetization ( M S ) [ 37 ].…”

Superparamagnetic cobalt ferrite nanoparticles as T 2 contrast agent in MRI: in vitro study

“…Secondly, MNPs smaller than 7 nm could not positively affect the r 2 relaxivity. However, slightly higher sizes could be optimal for the enhancement of the r 2 relaxivity [15, 17].…”

“…r 2 / r 1 is an indicator of MRI efficiency that increases with the increment of field strength [13]. Some studies evaluated CoFe 2 O 4 MNPs as MR contrast agent in different sizes and various magnetic fields, confirming the above‐mentioned content [2, 14–17]. The studies indicated that high r 2 / r 1 was obtained in large sizes and high magnetic fields.…”