Characterization of Gd loaded chitosan-TPP nanohydrogels by a multi-technique approach combining dynamic light scattering (DLS), asymetrical flow-field-flow-fractionation (AF4) and atomic force microscopy (AFM) and design of positive contrast agents for molecular resonance imaging (MRI)

Abstract

Chitosan CS-tripolyphosphate TPP/hyaluronic acid HA nanohydrogels loaded with gadolinium chelates (GdDOTA ⊂ CS-TPP/HA NGs) synthesized by ionic gelation were designed for lymph node (LN) MRI. In order to be efficiently drained to LNs, nanogels (NGs) needed to exhibit a diameter ϕ < 100 nm. For that, formulation parameters were tuned, using (i) CS of two different molecular weights (51 and 37 kDa) and (ii) variable CS/TPP ratio (2 < CS/TPP < 8). Characterization of NG size distribution by dynamic light scattering (DLS) and asymetrical flow-field-flow-fractionation (AF4) showed discrepancies since DLS diameters were consistently above 200 nm while AF4 showed individual nano-objects with ϕ < 100 nm. Such a difference could be correlated to the presence of aggregates inherent to ionic gelation. This point was clarified by atomic force microscopy (AFM) in liquid mode which highlighted the main presence of individual nano-objects in nanosuspensions. Thus, combination of DLS, AF4 and AFM provided a more precise characterization of GdDOTA ⊂ CS-TPP/HA nanohydrogels which, in turn, allowed to select formulations leading to NGs of suitable mean sizes showing good MRI efficiency and negligible toxicity.

Biocompatibility of Gd-Loaded Chitosan-Hyaluronic Acid Nanogels as Contrast Agents for Magnetic Resonance Cancer Imaging

“…No topological differences could be noticed according to CS concentration, the acid or the gadolinium contrast agent. In any case, nanogels (NGs) diameters calculated from the AFM images were highly inferior to 100 nm ( Table 2 ) as already demonstrated before [ 67 ].…”

“…Since these nanogels are designed for lymphatic system imaging it is important to evaluate their in vitro effects towards dedicated cell lines, such as SVEC4-10 murine lymph node cells. A preliminary study conducted with this cell line [ 67 ] seemed to indicate that under certain conditions, results similar to those demonstrated for A20 lymphocytes were obtained. To have a better insight of the biological effects induced by Gd nanogels on SVEC4-10 murine lymph node cells, the impact towards these cells of CS-HA nanogels synthesized with two CS concentrations (1.5 and 2.5 mg·mL −1 ) and two paramagnetic Gd chelates (GdDOTA and GdDOTP) was evaluated.…”

“…We have recently shown that in order to have a better insight in nanogel mean sizes, DLS data should be systematically consolidated by AFM observations in tapping mode [ 67 ]. Moreover, when AFM is performed in liquid mode, that is, in conditions close to the ones used in DLS, this technique is particularly well suited to image fragile samples such as hydrogels because friction and shear forces are negligible.…”

“…Therefore, AFM is more reliable to distinguish between individual nanoparticles and particle aggregates. By DLS, this is trickier and results in an overestimation of nanoparticle size [ 67 ]. AFM images were acquired in liquid mode for all the nanosuspensions ( Figure 1 ).…”

“…We have recently shown that in order to have a better insight in nanogel mean sizes, DLS data should be systematically consolidated by AFM observations in liquid mode [ 67 ]. Indeed, AFM is particularly well suited since this technique requires not only experimental conditions that are not invasive for nanogels but also no application of mathematical models to obtain size information.…”