Smart hydrogels for shape deformation: mechanism, preparation, and properties

Abstract

Hydrogels are widely used in many applications due to their hydration environment and tunable properties (e.g., mechanical, chemical, and biocompatibility) similar to that of natural extracellular matrices. Upon exposure to some specific stimuli, hydrogels can undergo shape deformation or even state transitions, and these stimulus-responsive hydrogels are constantly being developed, with promising applications in biomedicine, micromechanics, soft actuators, and robotics. In recent years, there have been increasing studies on stimulus-responsive smart hydrogels, which incorporate driving units in previously studied high-strength hydrogels, allowing the hydrogels to not only retain their original excellent mechanical properties, but also have good driving properties. Herein, by analyzing the driving mechanism and driving modes of hydrogels, the latest progress in smart hydrogels with six different driving modes, such as temperature-driven, light-driven, pH-driven, substance-specific-driven, magnetic-driven, and hybrid-driven hydrogels, is explored. Also, the preparation, structure, and properties of hydrogels are reviewed in detail. Finally, the current challenges and future prospects for shape-deformation stimulus-responsive hydrogels are discussed.