Hydrogels formed through regulated self-organization of gradually charging chitosan in solution of xanthan

Abstract

Hydrogels are prepared by means of progressive acidification of xanthan solution containing dispersed chitosan particles in noncharged state at pH a little larger than pK_a of this polysaccharide. The following pH shift causes gradual charging of chitosan macromolecules that are involved into electrostatic interactions with oppositely charged xanthan. This triggered self-regulating processes of polysaccharide self-organization into supramolecular structures. Fibrillation or capsulation was observed that depended on the charge mixing ratio between chitosan and xanthan. The jellification of solutions took place in a case of fibrillar morphology. The strongest hydrogels were found where a fine and dense network of aligning fibrils of mean diameter of around 30 nm were generated. Where oppositely charged polysaccharides self-organized into capsules, the hydrogel was not formed because of the absence of cross-links between particles that could reach few mm in diameter and had mechanically strong shell.