Rheological characterisation of thermogelling chitosan/glycerol-phosphate solutions

In this study we demonstrate that chitosan solutions can be neutralised up to physiological pH (∼7.2) using β-glycerol phosphate without creating immediate gel-like precipitation and furthermore that subsequent heating of these solutions induces hydrogel formation. The addition of the particular basic salt, glycerol phosphate, provides the correct buffering and other physicochemical conditions including control of hydrophobic interactions and hydrogen bonding which are necessary to retain chitosan in solution at neutral pH near 4°C and furthermore to allow gel formation upon heating to 37°C. Rheological investigation evidenced the endothermic gelation of chitosan/β-glycerol phosphate solutions and allowed the establishment of a sol/gel diagram. The gelation process appears to be governed by delicate interplay between the pH and the temperature. The role of β-glycerol phosphate is discussed in the light of relevant literature particularly those indicating the role of glycerol and polyols in the stabilisation of proteins and polysaccharides.