Sol-gel transition of aqueous chitosan-ßglycerophosphate solutions

Hydrogels represent reliable systems for the delivery of drugs, including those based on nucleic acids. Indeed, hydrogel nature, structure, and response to physiological or external stimuli strongly influence the delivery mechanisms of entrapped active molecules, making hydrogel very attractive for many pharmacological and biomedical applications. In this study, the attention was focused on a thermo-gelling hydrogel, composed of chitosan/β-glycero-phosphate, which can be injected in situ and induced to gelify at physiological pH and temperature. Particular care was devoted to study the effect of temperature on the gelation kinetics and on the gel final properties, two very important aspects in the light of clinical applications. The rheological characterization (temperature and frequency sweep test) evidenced the important effect of temperature (15°C ≤ T ≤ 47°C), on both the gelation kinetics and the gel final properties. In particular, we found that similar slow gelation kinetics and weak gels occurred below 30°C while similar faster gelation kinetics and stronger gels took place for T ≥ 30°C. This result was confirmed by means of a Low Field NMR (LF-NMR) characterization. Interestingly, it was possible evaluating, by means of rheology and LF-NMR, the time evolution of the polymeric network mesh size upon gelation. Thus, the importance of rheology in a socially relevant field (drug delivery) is evident