Physicochemical and structural characterization of a polyionic matrix of interest in biotechnology, in the pharmaceutical and biomedical fields

This paper reports on the swelling degree and the rheological and structural characteristics of a hydrogel composed by chitosan and xanthan. The latter is a polyionic hydrogel obtained by complexation between the both polysaccharides. The swelling degree has been found to be influenced by the time of coacervation, the pH of the solution of chitosan used to form the hydrogel and the pH of the swelling solution. The molecular weight and the degree of acetylation of the chitosan also influence the swelling degree of this matrix. The connectivity between chitosan and xanthan affects the swelling degree of this matrix. A rheological study has been carried out in order to understand the formation of the coacervate and of the subsequent hydrogel. The evolution of the storage modulus with time during the coacervation has allowed to optimize the time of coacervation required for a subsequently hydrogel, with desirable swelling degree. The kinetics has shown that (a) the coacervate is formed in two distinct steps and (b) the storage modulus of the hydrogel reaches a stable plateau. The values of the storage modulus have been correlated with the swelling degree. The microscopic characterization has shown the presence of a porous network with a fibrillar structure. To complete the characterization studies fine powder of this hydrogel has been used to determine the surface, perimeter, Feret diameter and sphericity factor distribution of dry and hydrated (swollen) particles.