I've been trying to synthesize a chitosan(CS)/B-glycerol phosphate (B-GP) hydrogel that geliffies at 37oC without success, I only end with a really viscous solution after one week at 37oC. The chitosan (CS) I'm using has a molecular weight between 50 and 190 kDa and a deacetylation degree (DDA) of 75-85% I've read lots of papers. First I tried to reproduce the protocol of Preparation and Biodegradation of Thermosensitive Chitosan Hydrogel as a Function of pH and Temperature (Macromolecular Research, Vol. 12, No. 5, pp 507-511 (2004)). They use a CS with 161kDa and DDA=80% and prepare a 2% CS solution in 0,1M of HCl, and a 10% B-GP solution in water. Mix the solution and in 5 to 15min at 37oC they obtain a hydrogel.

=> I tried this but I couldn't get my CS dissolved in HCl 0,1M. Now I'm trying with the protocol of Effects of Chitosan Characteristics on the Physicochemical Properties, Antibacterial Activity, and Cytotoxicity of

Chitosan/2-Glycerophosphate/Nanosilver Hydrogels (doi:10.1002/app.37855) With a similar protocol but dissolving the CS in 0,1M fo HAc they obtain an hydrogel at 36oC with a CS of 161kDa and DDA=80%.

=> I do the same but I obtain a viscous solution. I've also read all of this papers: Characterization of thermosensitive chitosan gels for the sustained delivery of drugs (International Journal of Pharmaceutics 203 (2000) 89–98)

Novel injectable neutral solutions of chitosan form biodegradable gels in situ (Biomaterials 21 (2000) 2155-2161)

Rheological characterisation of thermogelling chitosan/glycerol-phosphate solutions (Carbohydrate Polymers 46 (2011) 39-47)

Physical Gelation of Chitosan in the Presence of B-Glycerophosphate: The Morphology and gelation of thermosensitive chitosan hydrogels (Biophysical Chemistry 117 (2005) 47 – 53)

Effect of Temperature (Biomacromolecules 2005, 6, 3267-3275)

Chitosan and glycerophosphate concentration dependence of solution behaviour and gel point using small amplitude oscillatory rheometry (Food Hydrocolloids 20 (2006) 936–945)

Glycerophosphate-based chitosan thermosensitive hydrogels and their biomedical applications (Carbohydrate Polymers 117 (2015) 524–536)