Dual Temperature- and pH-Responsive Self-Healing Hydrogels Based on Dynamic Imine Networks: Design, Characterization, and Applications in Industrial Processes and Drug Delivery

Abstract

Stimuli-responsive polymers that repair damage in an autonomous fashion are attractive for equipment, protective coatings and pharmaceutical therapy. Here we describe the design, synthesis and characterization of a dual-responsive hydrogel based on a dynamic imine (Schiff-base) cross-link of chitosan with benzaldehyde-terminated poly(ethylene glycol) in the presence of poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AA)]. The composition of the polymer can be adjusted for the lower critical solution temperature (LCST) from 32.0 to 36.8 °C. The swelling is greater in acidic media and the imine network forms again after the damage with 96% healing efficiency in 16 h with pH 5.0 compared to 82% with pH 7.4. Doxorubicin release at 37 °C is 93% at pH 5.0 whereas 38% at pH 7.4 for 48 h and the release exponents indicate anomalous transport. FTIR, TGA/DTG and DSC show imine formation and thermal stability up to 285 °C and calorimetric LCST of 31.6-38.0 °C. XRD shows mainly amorphous network, UV–Vis spectroscopy measures the optical transition process, pH-dependent imine kinetics (at pH 5), and loading of doxorubicin (up to 78% encapsulation efficiency) are determined.