In-situ cryo-SEM investigation of porous structure formation of chitosan sponges

Aiming at better understanding of porous structure formation unique in-situ experiments on freeze-drying the chitosan-based solvents were carried out by cryo-SEM method. It allowed us to visualize the lyophilization process and to follow the formation of the porous structure in the chitosan sponge. It was clearly shown that the chitosan solutions just after freezing possess an evident microstructure consisting of the walls of the future pores and of the frozen solvent filling the space between them. The diameter of the pores and their wall thickness are controlled be pre-freezing temperature. An incorporation of nanofillers (chitin nanofibrils and montmorillonite) into the chitosan solution did not affect the pore size and wall thickness. However, they can promote the formation of the layered structure of the pore walls.