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

Abstract

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.

Keywords: Carboxymethylchitosan; Dynamic covalent bond; Hydrogels; Imine clip; Rheology; Transimination; X-ray diffraction.