Rapidly Thermoresponsive Poly( N -isopropylacrylamide) Hydrogels Enabled by Itaconic Acid-Modified Cellulose Fiber Cross-Linkers

Abstract

Stimuli-responsive hydrogels capable of reversible volume change are promising materials for soft actuators, sensors, and biomedical systems. However, conventional poly(N-isopropylacrylamide) (PNIPAAm) hydrogels typically exhibit slow thermal responses due to limited water transport and the formation of a dense skin layer during phase transition. In this study, a cellulose fiber-based cross-linker (Cel-IA) was prepared by modifying cellulose with itaconic anhydride and incorporated into PNIPAAm hydrogels via free-radical polymerization. The resulting Cel-IA-cross-linked hydrogels exhibited significantly accelerated thermoresponsive behavior compared with conventional and CNF-blended PNIPAAm hydrogels. Rapid deswelling at 50 °C was achieved within minutes, accompanied by dynamic changes in surface wettability. This enhancement is attributed to the rigid and hydrophilic cellulose framework, which acts as a nanoscale spacer and forms hydrophilic pathways that facilitate water diffusion and suppress the dense-skin effect during the phase transition of PNIPAAm chains. Furthermore, bilayer hydrogels composed of a nonthermoresponsive layer and a Cel-IA–PNIPAAm layer demonstrated rapid temperature-driven actuation, bending within 1 min. By integrating a cellulose- and itaconic acid-derived sustainable cross-linking component, this work provides a pathway toward high-performance, environmentally conscious thermoresponsive hydrogels. These results demonstrate that cellulose-derived cross-linkers offer a robust strategy for designing fast-response thermoresponsive hydrogels for soft actuator applications-PNIPAAm layer demonstrated rapid temperature-driven actuation, bending within 1 min. By integrating a cellulose- and itaconic acid-derived sustainable cross-linking component, this work provides a pathway toward high-performance, environmentally conscious thermoresponsive hydrogels. These results demonstrate that cellulose-derived cross-linkers offer a robust strategy for designing fast-response thermoresponsive hydrogels for soft actuator applications.