Rheological Characterization of Hydrogels of Alginate-Based Nanodispersion

The interest in alginate-based systems is due to the wide potential of application of this macromolecule in several fields ranging from pharmaceutical, medical to coating and food industries. Here, we present alginate-based hydrogels prepared through the in situ gelation method [1] driven by calcium cross-linking. The gelation process was applied on oil-in-water nanodispersions of lemongrass essential oil in alginate, stabilized by a non-ionic surfactant (Tween 80). Hydrogels prepared at different concentrations of alginate (0.5-1%), essential oil (0, 0.1 and 0.5%) and calcium (4, 6, 8 and 10 mM) were characterized for their rheological behavior. First, flow curves demonstrated that all the hydrogels shared pseudoplastic behavior. Then, oscillatory tests showed that the strength of the hydrogel network increased with the crosslinker increase and decreased at low polymer concentrations [2, 3]. Hydrogels were also characterized for their time-dependent behavior and resulted as thixotropic materials with a long time of structural restoration after breakage. Finally, creep-recovery experiments that were all fitted to the Burger model, showed that hydrogels with low alginate concentration were more deformable and that the deformation was reduced by the increase of oil content. On the other hand, the deformability decreased both with the alginate and the crosslinker concentration increase. The outcomes of this study showed that the mechanical characteristics of the proposed hydrogels were mainly influenced by the concentration of alginate and the crosslinking agent.