Carboxyalkylchitosan-based hydrogels with "imine clip": Enhanced stability and amino acids-induced disassembly under physiological conditions.

Here we report on the properties of hydrogels of carboxyalkylchitosans-salicylimines depending on the salicylaldehyde (SA) grafting density, type of carboxyalkyl substitution, pH, and presence of amino acids. The mechanism of SA grafting has been investigated using 13C NMR and FT-IR spectroscopy and elemental analysis. We have found that, despite lower SA grafting density to carboxyalkylchitosans, gelation in these solutions occurred at much lower SA:polymer molar ratios than for chitosan-salicylimines, being the highest for a N-carboxyethylchitosan with a medium substitution degree. Controlled disassembly of supramolecular architecture of hydrogel of N-carboxyethylchitosan-salicylimine at physiological pH was achieved via the transimination reaction in the presence of amino acids with the efficiency decreased in the order: lysine > arginine ≥ serine. Application of carboxyalkylchitosans opens a new window for development of salicylimine-based hydrogels with lower SA grafting density, better mechanical properties, and reversibility in a broader pH range than it was earlier known for chitosan-based biodynamers.