Étude des propriétés de transport dans les hydrogels de curdlan

Polysaccharide hydrogels are biomaterials used as controlled drug delivery matrices and serve as model scaffolds for the study of many biological systems like bacterial biofilms and mucus.  In every case, the transport of drugs or nutriments across a hydrogel matrix is of prime importance.  Therefore, the study of transport properties in hydrogels is an important issue for many fields of application. In this work, curdlan, a neutral bacterial polysaccharide made of  β-D-(1→3) glucose repeating units, is used as a model hydrogel.  Aqueous suspensions of curdlan can form thermogels of different conformations depending on the incubation temperature.  In situ characterization of the preparation of thermo-reversible (low-set) and thermo-irreversible (high-set) curdlan hydrogels was first carried out using variable temperature attenuated total reflection (ATR) Fourier transform infrared spectroscopy (FT-IR).  The results allowed optimization of the gelling conditions leading to reproducible gel samples. Structural characterization of fully hydrated hydrogels, carried out by FT-IR imaging, environmental scanning electron microscopy (eSEM) and atomic force microscopy (AFM), allowed visualization of the different gel morphologies susceptible of influencing the diffusion of analytes in hydrogels.  Our results show that both types of curdlan hydrogels have distinct microscopic architectures. The combination of pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and NMR profiling allowed the study of self-diffusion and mutual diffusion on the same hydrogel system in similar experimental conditions.  We showed that the diffusion of analytes in the gels is slower than in the aqueous solution.  The diffusion experiments, carried out on a series of analytes of various sizes in both types of curdlan gels, show a decrease of the relative self-diffusion coefficient as a function of the analyte size.  In addition, our results suggest that the equivalence between the self-diffusion and mutual-diffusion coefficients measured in the high-set curdlan gels is mainly due to the fact that the environment probed by the analytes during a self-diffusion experiment is representative of the one probed during a mutual-diffusion experiment.  In such conditions, our results show that PFG NMR may present a valuable approach for the characterization of controlled drug release systems.  Additional experiments show that the mutual-diffusion coefficient of dextran macromolecules is smaller than its self-diffusion coefficient in the same curdlan hydrogel.  The difference between both transport rates is attributed to the different environment volumes probed by the analytes during the measurements. The similarities observed between the self-diffusion and mutual-diffusion coefficients, measured in both types of curdlan gels for all investigated analytes, suggest a limited influence of the microscopic gel architecture on its transport properties.  It is therefore concluded that the interactions affecting the diffusion of the investigated analytes in the curdlan hydrogels lie at the molecular scale.

Keyphrases: Curdlan, Hydrogel, Profilage RMN, Curdlan, Hydrogels, Self-diffusion, Mutual diffusion, Pulsed field gradient (PFG) NMR, NMR profiling, Fourier transformed infrared spectroscopy (FT-IR), Attenuated total reflection (ATR), FT-IR imaging