Figure 2.

(a) Schematics for the programmable process of the snowflake shaped SMSC hydrogel film. Optical images of the snowflake shaped SMSC hydrogel film in 45 °C water. The bending angles in (b): (i) 0°, (ii) 30°, (iii) 50°, (iv) 80°, (v) 90°. Reproduced with permission [11]. Copyright 2022, ELSEVIER. (b) Microcantilever bending and recovery are induced by changes in pH values, where θ is the bending angle. Reproduced with permission [15]. Copyright 2021, American Chemical Society. (c) Photographic images of WNE actuators with different thicknesses operating at 3 V. Reproduced with permission [19]. Copyright 2022. The Authors, some rights reserved, exclusive licensee American Association for the Advancement of Science. (d) Formation of compound micromachines with a bilayer head and monolayer tail. Due to the lack of particle alignment, the folding axis of the head is solely determined by the edge effect. Finite element modeling (FEM) simulations visualize internal stress distribution. Reproduced with permission [22]. Copyright 2016, Springer Nature. (e) Mechanism of the hygroinduced locomotion of PCAD@AG films. For each aspect ratio and stage of locomotion, both cartoons and snapshots of the real film are shown. Top I–IX: Square-shaped film, middle I–IX: rectangular film and bottom I–VIII: film strip. Reproduced with permission [26]. Copyright 2015, Springer Nature. (f) the structural changes of actuators with H-, U-, S-, and T-shape patterns under the stimuli of humidity and IR light. Reproduced with permission [25]. Copyright 2019, Springer Nature. (g) Site-specific bending of the Janus film. Reproduced with permission [48]. Copyright 2017, Springer Nature.