Stiffness xanthan hydrogels: synthesis, swelling characteristics and controlled release properties

New xanthan hydrogels were synthesized at 90 C in water acid media using adipic acid dihydrazide (ADH) as crosslinking agent, in the presence of 1-ethyl-3[3-dimethyl amino] propyl carbodiimide hydrochloride (EDCI) as reagent. In these conditions, xanthan chains are in a predominantly helical conformation and through rheological measurements the influence of the temperature over the helix-coil transition was assessed. Xanthan hydrogels with different concentration in polysaccharide and ADH were obtained and characterised by elemental analysis and swelling properties. High concentration of xanthan (i.e. 25gL(-1)) is needed to obtain gel due to the low available carboxylic functions in the helical conformation. During the swelling analysis, it was noted that high temperature (i.e. 90 C) favoured the conformational transitions within the network. The drug loading and releasing properties were estimated using methylene blue as model molecule and different experimental pH and ionic strength conditions.