Effect of chitosan characteristics and solution conditions on gelation temperatures of chitosan/2-glycerophosphate/nanosilver hydrogels

In this study, we explored the effect of nanosilver, chitosan characteristics, and solution conditions on gelation temperatures of chitosan/2-glycerophosphate thermosensitive hydrogel. The gelation temperatures of hydrogels with or without 12 ppm nanosilver were insignificantly different regardless of the molecular weight (MW) of chitosan (degree of deacetylation, DD, 80% or 88%) and glycerophosphate concentration. The gelation temperature of hydrogel decreased with increasing DD (65-88%) of chitosan, increasing concentration of glycerophosphate (2-8%), and increasing pH value (6.5-6.8). It also decreased with decreasing chitosan's MW (DD88: 113-345 kDa, DD80: 145-900 kDa), but increased with increasing concentrations of NaCl (0-2%). By adjusting above conditions, the hydrogel gelation can be induced with a temperature range from 24.3 to 91.7 °C. Chitosan chains with higher flexibility and/or smaller hydrodynamic volume resulted in lower gelation temperature. Hydrogel became white turbidity in 2% NaCl below 38 °C because of its lower solubility at higher ionic strength.