Fig. 1. (Color online) Methods and applications of thermally actuated reconfiguration. (a) Shape evolution of two morphable mesostructures made of shape-memory polymers. Reproduced with permission from Ref. [32]. Copyright 2018, AAAS. (b) Shape evolution of LCE with mesogens aligned in groups. Reproduced with permission from Ref. [22]. Copyright 2015, AAAS. (c) Demonstration of a thermally actuated micro-tweezer made of SMA. Reproduced with permission from Ref. [18]. Copyright 2007, IOP Publishing Ltd.

Fig. 2. (Color online) Methods and applications of chemically actuated reconfiguration. (a) Shape evolution of an ionoprinted hydrogel subject to different solvents. Reproduced with permission from Ref. [60]. Copyright 2013, Macmillan Publishers Limited. (b) Schematic illustration of a 3D jump micro hydrogel device, and scanning electron microscope (SEM) image of embedded microfluidic channels. Reproduced with permission from Ref. [61]. Copyright 2010, The Royal Society of Chemistry. (c) Evolution of the micro hydrogel device induced with a liquid solvent. Reproduced with permission from Ref. [61]. Copyright 2010, The Royal Society of Chemistry. (d) 2D-to-3D shape transformation of a tri-layer hydrogel subject to a variant pH. Reproduced with permission from Ref. [68]. Copyright 2014, John Wiley & Sons Inc.

Fig. 3. (Color online) Methods and applications of optically actuated reconfiguration. (a) Bending of a cantilever made of LCE with azobenzene under the exposure of light with different polarization angles. Reproduced with permission from Ref. [80]. Copyright 2011, The Royal Society of Chemistry. (b) Rolling of a LCE film induced through the application of visible and UV light. Reproduced with permission from Ref. [82]. Copyright 2008, John Wiley & Sons Inc. (c) Shape evolution of a bilayer film with photo-initiated proton-releasing agent. Reproduced with permission from Ref. [ 67]. Copyright 2012, The Royal Society of Chemistry.

Fig. 4. (Color online) Methods and applications of magnetically actuated reconfiguration. (a) Milli-robots made of magnetoelastic soft materials. Reproduced with permission from Ref. [92]. Copyright 2018, Macmillan Publishers Limited. (b) Navigation of a ferromagnetic soft continuum robots through 3D cerebrovascular phantom network. Reproduced with permission from Ref. [96]. Copyright 2019, AAAS.

Fig. 5. (Color online) Methods and applications of electrically actuated reconfiguration. (a) Schematic illustration of a robotic fish made of DE (left-hand panel), and forward motion of the fish (right-hand panel). Reproduced with permission from Ref. [110]. Copyright 2017, AAAS. (b) Shape reconfiguration of four actuators made of IPMC (top panel), and working process of a three-finger gripper (bottom panel). Reproduced with permission from Ref. [101]. Copyright 2008, Cambridge University Press. (c) Movement of an insect-scale robot made of PVDF. Reproduced with permission from Ref. [118]. Copyright 2019, AAAS.

Fig. 6. (Color online) Methods and applications of mechanically actuated reconfiguration through the use of different strain release paths. (a) Illustration of the strategy through a sequence of FEA results and a pair of colorized SEM images for the two stable configurations. (b) SEM images and FEA predictions of morphable, recognizable objects. (c) Exploded view of the layer construction for a morphable electromagnetic device with shielding capability. (d) Optical images and FEA predictions of the device. (e) Simulated radiant efficiency of three antennas at two different stable shapes. Reproduced with permission from Ref. [137]. Copyright 2018, Macmillan Publishers Limited.

Fig. 7. (Color online) Methods and applications of mechanically actuated reconfiguration assisted by kirigami substrate designs. (a) Conceptual illustration of the fabrication process, through a sequence of FEA results. (b) Two-dimensional geometries, FEA predictions, and scanning electron microscope images of a 3D morphable trilayer microstructure as mechanically tunable optical chiral metamaterials. (c) Measured and simulated optical circular dichroism of the 3D trilayer microstructure with two 3D shapes in the 0.2–0.4-THz frequency range. Reproduced with permission from Ref. [5], Copyright 2019, National Academy of Sciences.

Table 1. Summary of reconfiguration methods.