Irradiating or autoclaving chitosan/polyol solutions: effect on thermogelling chitosan-beta-glycerophosphate systems

The effects of steam sterilization and gamma-irradiation on chitosan and thermogelling chitosan-beta-glycerophosphate (GP) solutions containing polyol additives were investigated. The selected polyols were triethylene glycol, glycerol, sorbitol, glucose and poly(ethylene glycol) (PEG). They were incorporated to chitosan solutions prior to sterilization in a proportion ranging from 1 to 5% (w/v). The solutions were characterized with respect to their viscosity, thermogelling properties, compressive stress relaxation behavior and chitosan degradation. All polyols reduced the autoclaving-induced viscosity loss and had a positive impact on the solution thermogelling properties and compressive performance of the gels. Steam sterilization in the presence of glucose resulted in a substantial increase in the solution viscosity and gel strength. This was associated with a strong discoloration suggesting chemical alteration of the system. PEG was the most effective agent in preventing hydrolytic degradation of chitosan chains. Gamma-irradiation strongly decreased the chitosan solution viscosity regardless of the presence of additives, even when sterilization was carried out at -80 degrees C. Moreover, the thermogelling properties were dramatically altered, and thus, gamma-irradiation would not be an appropriate method to sterilize chitosan solutions. In conclusion, polyols are potentially useful additive to maximise the viscoelastic and mechanical properties of chitosan-GP after steam sterilization.