Anionic Polysaccharide Hydrogels with Charges Provided by the Polysaccharide or the Crosslinking Agent

Polysaccharides have attractive advantages for using in the field of pharmaceutics. In most cases, they are non toxic, biocompatible and plentiful. The presence of hydroxyl groups (always) and carboxylic acid groups (sometimes) permits crosslinking of the chains and obtaining hydrogels. These hydrogels present interesting swelling and mechanical properties. They have the capacity to entrap active compounds such as drugs and release them through modifications of the solvation conditions vias pH or ionic strength changes. This review deals with polysaccharide hydrogels obtained by the formation of covalent bounds between polymeric chains. We have focused our attention on systems with an anionic character. These charges are due to the presence of acidic functions on the polysaccharide backbone or are brought by the crosslinking agent. The anionic character dependents on the ionic strength and pH. We discuss the synthesis of these hydrogels. After a short presentation of a few polysaccharides, we describe the different crosslinking agents and their action mode. Applications in drug delivery are discussed along.