Intelligent Hydrogel Actuators With Controllable Deformations and Movements

Abstract

Near infrared laser- (NIR-) driven intelligent hydrogel actuator systems including printable N-isopropylacrylamide- (NIPAm-) nanosized synthetic hectorite clay-nanofibrillated cellulose (NFC) hydrogels and NIPAm-4-hydroxybutyl acrylate- (4HBA-) NFC hydrogels with a high response rate were prepared via three-dimensional (3D) printing and hydrothermal synthesis, respectively. The addition of NFC was beneficial to the improvement in rheology. The 3D printed intelligent hydrogel actuators with a structure pattern of Model I and Model II exhibited the saddle and inverted saddle deformations, respectively, to prove the validity of 3D printing. In order to improve the response rate and enrich movement patterns, the hydrothermal synthesized intelligent hydrogel actuators were prepared on the base of the 3D printed intelligent hydrogel compositions. The addition of NFC maintained the controllable NIR response. Based on a wedge-shaped design, the hydrothermal synthesized intelligent hydrogel pushed the resin ball with weight of 130 mg forward 8 mm in 39 s. By changing the torque values of a hydrogel in a different direction, the actuator realized controllable continuous rollover movement. Attributed to the longilineal shape, the intelligent hydrogel actuator reached an effective displacement of 20 mm in 10 s via a forward movement. The characteristics and structure design of a hydrogel material significantly realized multiple controllable functional four-dimensional (4D) printed deformations and movements. The combination of advantages of the 3D printed and hydrothermal synthesized intelligent hydrogels provided a new direction of development and abundant material candidates for the practical applications of 4D printing in soft robot, information sensing, and health engineering.