Atypical polysaccharide physical gels: Structure/property relationships

Chitin and chitosan are polysaccharides produced by the biomass. They have the same general chemical structure and constitute the series of linear copolymers of linked beta, (1-->4) glucosamine and N-actylglucosamine. We studied the possibility of forming physical gets with all the terms of this series, whatever the proportion of the two kinds of residues included in the polymer chains. We show that physical gelation is still possible through a percolating process when certain important conditions are met. Initially the concentration in polymer must be above C*; a critical value of the balance between hydrophobic and hydrophilic interactions must be achieved and gelation must occur simultaneously everywhere in the medium. These conditions were observed in several situations allowing the formation of different kinds of gels at all values of DA. In view of the rare bioactive properties of chitin and chitosan, these gels were tested for living tissue regeneration and constitute very interesting examples in illustration of our concept of decoys for biological media.