Polyelectrolytic nature of chitosan: Influence on physicochemical properties and synthesis of nanoparticles

Abstract Chitosan is an excellent polymer that has been exploited for biomedical applications ranging from antimicrobial action to targeted drug delivery and tissue engineering. Chitosan has been chiefly used to develop formulations in the form of conjugates, nanoparticles, hydrogels and scaffolds. However, being a polyelectrolyte, the charge density and various physicochemical properties, such as solubility, viscosity, mucoadhesion, and swelling of chitosan, are extremely sensitive to variation in external conditions (e.g., pH and ionic strength of the medium). This review discusses chitosan's physicochemical properties in the solution like solubility, viscosity, mucoadhesion, and swelling, which are a function of its polyelectrolytic nature. Furthermore, the effect of specific parameters like pH and ionic strength of the medium on the polymer and nanoparticle synthesis is also discussed. During formulation development process the charge density on chitosan plays a crucial role in determining the final product's efficiency. Finally, we conclude that the effectiveness of cellular adherence of chitosan hydrogels or scaffolds, the biodistribution of nanoparticles, and the antimicrobial action of chitosan are all functions of its surface charge density.