Carboxymethylpullulan hydrogels with a ionic and/or amphiphilic behavior: Swelling properties and entrapment of cationic and/or hydrophobic molecules

New ionic and amphiphilic polysaccharide-based hydrogels were synthesized and evaluated for controlled release entrapment applications. The starting polysaccharide (pullulan) was first carboxymethylated to provide ionic derivatives. The hydrogels were then obtained by cross-linking carboxymethylpullulan with adipic acid dihydrazide in water in the presence of 1-ethyl-3-[3-(dimethylamino)-propyl]carbodiimide hydrochloride (EDCI) as reagent. A set of hydrogels differing by their cross-linking densities was prepared and their degree of swelling were measured in water and in the presence of sodium chloride (0.1 mol L−1). The entrapment capacity of hydrogels was estimated using two probe molecules: methylene blue, a cationic dye with a high affinity with negatively charged compounds and coomassy brilliant blue, a molecule having a marked amphiphilic character. The ionic and/or amphiphilic properties of the hydrogels were then demonstrated by their capacity or not to entrap these molecules.