fig3

Figure 3. Mechanisms of responsive contraction and expansion of the films. (A) Water-responsive supercontractile polymer films due to crystalline transition. Copyright 2023, Springer Nature^[30]; (B) Thermo-responsive contraction adhesive hydrogel films due to critical temperature transitions. Copyright 2019, American Association for the Advancement of Science^[30]; (C) Light-induced contraction and expansion mechanism from a hydrogel film with photo-responsive spiropyran molecules. Copyright 2024, Springer Nature^[112]; (D) Fabrication of light-responsive films with controlled expansion due to hydrophobic-hydrophilic transition. Copyright 2019, John Wiley and Sons^[91].