Polysaccharide-based hydrogels: structure and function

Biopolymer-based hydrogels with a tuneable structure have drawn significant attention due to their wide range of applications in the food, pharmaceutical, and biomedical fields. This can be attributed to their remarkable features such as desirable mechanical properties, high water content, biodegradability and biocompatibility. At first order, hydrogels can be described as a network containing a crosslinked polymer and open spaces (meshes) between polymers chains enabling the diffusion of liquids and entrapped molecules such as proteins, peptides, and vitamins.In this work, we prepared polygalacturonate-based hydrogels by diffusing divalent cations X2+ (eg., Ca2+, Zn2+, Fe2+) from an external reservoir, through a dialysis membrane, to the polygalacturonate (polyGalA) solution. These hydrogels exhibited various degrees of inhomogeneity and showed a significant gradient of both polyGalA and divalent cation concentrations, ranging from the part of the gel formed near the dialysis membrane (i.e., the initial stage of the gelation process) to the furthest part of the gel. We demonstrated that Fe2+ cations keep their +II oxidation sate in the entire gel, making them suitable for iron fortification purposes.1 Furthermore, we observed that the mesh size () in the regions of the gel closer the dialysis membrane remained close to 7.5 nm, regarless of the divalent cation used (Ca2+, Zn2+, Fe2+).2 However, in the farthest parts of the gel, the mesoscopic structure depended on the nature of the cation, particularly on the different modes of interaction known to occur between the cation and the GalA unit, such as bidentate versus “egg-box” geometry.AcknowledgementsLaboratoire Léon Brillouin, Synchrotron SOLEIL and Région Bourgogne Franche-Comté are acknowledged for their financial support.References1.Maire du Poset A, Lerbret A, Zitolo A, Cousin F, Assifaoui A, Design of polygalacturonate hydrogels using iron(II) as crosslinkers: A promising route to protect bioavailable iron againstoxidation. Carbohydr. Polym. 2018, 188, 276−283.2.Maire du Poset A, Lerbret A, Boué F, Zitolo A, Assifaoui A, Cousin F, Tuning the Structure of Galacturonate Hydrogels: External Gelation by Ca, Zn, or Fe Cationic Cross-Linkers. Biomacromolecules 2019, 20 (7), 2864−2872