Chitosan Hydrogels Prepared on the Basis of Polyelectrolyte Complexes (A Review)

The review is devoted to a unique approach that enables the formation of homogeneous chitosan hydrogels and films with oppositely charged biopolymers and inorganic nanoparticles in a self-organizing regime, controlled by regulated charging of the polysaccharide through the slow acidification by gluconic acid of the initial neutral solution, in which chitosan is added in an uncharged state. The acid is generated during the hydrolysis of non-toxic D-glucono-δ-lactone, widely used in the food industry. The prepared hydrogels and films are fundamentally differed from coacervates in their structure and properties, which also consist of polyelectrolyte complexes but in the form heterogeneous precipitate without any pronounced structural organization due to a rapid, uncontrollable cooperative processes. The review compares both methods, their experimental features, and differences in their mechanisms. Finally, examples of the functional materials that have been fabricated to date using controlled charging of chitosan are presented. The advantages of this approach are highlighted, including the process being carried out solely in aqueous solutions, without the addition of organic solvents, and at room temperature. Gelling is achieved only through physical interactions, eliminating the use of toxic cross-linking agents and reagents.