Stimuli-responsive hydrogel consisting of hydrazide-functionalized poly(oligo(ethylene glycol)methacrylate) and dialdehyde cellulose nanocrystals

Abstract

A self-healable thermo-responsive hydrogel was produced via the formation of acylhydrazone bond between dialdehyde-functionalized cellulose nanocrystals (DACNC) and hydrazide-functionalized poly(oligo(ethylene glycol) methacrylate) (POEGMA-H). POEGMA-H displayed a two-step phase transition upon increasing the temperature due to the coil to globule transition of the middle and end segments of the polymer chains. Rheological measurements revealed a significant increase in hydrogel stiffness (from 11 Pa to 1907 Pa) due to the coil to globule transition of POEGMA-H chains when the temperature was increased from 25 to 75 °C. With increasing concentration of DACNC, the stiffness of the hydrogel was enhanced. At low and medium pHs, stable hydrogels were formed, however, at high pH, gradual formation of acylhydrazone bonds led to a loose network. The hydrogel possessed self-healing capability with close to 100% recovery in the storage modulus at medium pH, and it has great potential in biomedical applications.