NMR Relaxometric Properties of SPION-Loaded Solid Lipid Nanoparticles

Abstract

Longitudinal and transverse relaxivities of solid lipid nanoparticles loaded with superparamagnetic iron oxide nanoparticles (SPION-SLNs) were thoroughly investigated with the aim of understanding the main parameters regulating the potential negative contrast properties of these systems. In particular, the longitudinal relaxivity (r 1) of water protons in the 10 kHz to 35 MHz frequency range was determined by 1H fast field-cycling NMR, while transverse relaxivity (r 2) was measured at 21 MHz. The reproducibility and stability of SPION-SLNs was also tested on samples arising from independent preparations and at different times after preparation. Water diffusion in proximity of superparamagnetic nanoparticles was found to be the mechanism of proton nuclear relaxation enhancement and characteristic parameters were quantitatively determined by fitting the experimental data acquired on different samples as a function of concentration and temperature. Although a variation ascribable to the formation of clusters with a different number of SPIONs inhomogeneously embedded in the lipid matrix was observed among different preparations, the relaxivity properties of the investigated SPION-SLNs were found to be better than those of SPION-based contrast agents commonly considered as standard in the literature, and remained stable for at least 2 months.

Feasibility of USPIOs for T1-weighted MR molecular imaging of tumor receptors

“…22,45 Clustering of USPIOs would dramatically enhance the T 2 contrast effect (r 2 ), while weakening the T 1 -shortening effect (r 1 ), resulting in high r 2 /r 1 ratio and limiting USPIOs to be a T 1 contrast agent. 46 Our results were actually in accordance with previous observations that intracellular connement of magnetite nanoparticles within micrometric endosomes led to a significant decrease of the r 1 relaxivity compared to that of the dispersed isolated nanoparticles. Consequently, for T 1 -weighted sequences, the signal intensity fell essentially, so the positive enhancement no longer existed.…”

Facile synthesis of superparamagnetic iron oxide nanoparticles with tunable size: from individual nanoparticles to nanoclusters

“…The nanoparticles exhibited an r 1 value of 12.15 mM −1 s −1 , whereas that for 20 and 32 nm nanoclusters were only 3.9 and 1.0 mM −1 s −1 , respectively. These results were consistent with previous observations that clustering would dramatically enhance the T 2 effect, while diminish the T 1 effect of SPIONs [33,34]. Nanoclusters of 32 nm had an r 2 value of 410 mM −1 s −1 , which was among the highest reported for IO nanomaterials [15,18].…”

From Single-Core Nanoparticles in Ferrofluids to Multi-Core Magnetic Nanocomposites: Assembly Strategies, Structure, and Magnetic Behavior

“…Allowing for encapsulation, retention, the membrane sealing off the interior of a hydrophilic volume from the environment, and the magnetic field-triggered release of the drug are the main attractive features of membranes-protected hollow nanocarriers for nanomedicine [152]. The loading of liposomes with iron oxide nanoparticles [153][154][155], mostly clusters preformed from aqueous [64,156,157] and organic [158,159] ferrofluids gives rise to magnetoliposomes with high magnetophoretic mobility and MRI contrast [160]. LipoMag composites [158] are assembled as oleic acid-coated magnetite nanocrystal cores with cationic lipid shells from a chloroform-based magnetic fluid through hydrophobic interactions [161,162] (Figure 5A).…”