Sticky Hydrogels from Hydrazide-Functionalized Poly(oligo(ethylene glycol) methacrylate) and Dialdehyde Cellulose Nanocrystals with Tunable Thermal and Strain-Hardening Characteristics

Thermoresponsive injectable hydrogels with a tunable transition temperature and adhesion are ideal for biomedical applications, where weak to moderate adhesion is required. Smart sticky hydrogels with tunable transition temperature and strain hardening were prepared by cross-linking hydrazide-functionalized poly(oligo(ethylene glycol) methacrylate) (POEGMA-H) with dialdehyde cellulose nanocrystals (DACNC), and their adhesive characteristics were elucidated. Probe-tack tests on hydrogels below and above the transition temperature revealed an increase in the stress and work of adhesion at the transition temperature due to unfavorable exposure of the collapsed chains to water. By increasing the percentage of OGEMA(300) monomer, the hydrogels displayed an increase in the stress and work of adhesion at their transition temperatures. Higher percentages of OGEMA(300) monomer yielded a thicker brush in the POEGMA-H polymer. As a result, the exposed area of the chain to water was enhanced during deformation, leading to the observed higher stress and work of adhesion.