Polymeric Supramolecular Hydrogels as Materials for Medicine - In-Situ Gelling Polymers: For Biomedical Applications - page 164

Fig. 11 Schematic representation of the formation of xanthan and chitosan polyelectrolyte
hydrogels through mutual ionic interaction. When chitosan and xanthan are mixed, a common
pH is established, and the polymer chains associate to each other. These first two steps are rapid
processes, followed by slow phase separation that is referred to as coacervation. In the coacer-
vation step, water molecules orient in between the polymer chains and form hydrogen bonds.
When all surrounding water molecules are oriented in this fashion, a polyelectrolyte hydrogel is
obtained. Reprinted from Dumitriu et al. [ 141 ]. Copyright 2004 Elsevier
At first, Dumitriu and collaborators investigated the swelling of hydrogels
composed of a high and a low molecular-weight chitosan with different coacer-
vation times before the preparation of the gels, spanning from no time of coac-
ervation over 4-24 h. The lower molecular-weight sample with no coacervation
time showed a high mass-swelling degree of 4,000 %, indicating weak association
between the polymer chains. After 4 h of coacervation, the mass-swelling degree
was smaller, 1,250 %, whereas the mass-swelling degree of the sample with high