Figure 22.

Photothermal actuators and robots. (a) Sequential actuation of shape-memory polymer films through the wavelength-selective photothermal heating of Au nanospheres and nanorods. The TEM images and extinction spectra of the Au nanospheres and nanorods are shown on the left panel. A wavelength-controlled stage is demonstrated on the right panel with optically controlled heights and tilt angles using two legs made of folded shape-memory polymer films embedded with the Au nanospheres and nanorods, respectively. Two light-emitting diodes are used to selectively drive the shape recovery of the two legs. Reprinted with permission from ref (578). Copyright 2018 American Chemical Society. (b) Schematics and photographs of PDA-coated LCN actuators, which can advance two steps through arching up/flattening down in a single on and off irradiation cycle. Reprinted with permission from ref (585). Copyright 2021 Xiao et al., published under the CC BY 4.0 license http://creativecommons.org/licenses/by/4.0/. (c) Earthworm-like directed peristaltic crawling enabled by an anisotropic hydrogel actuator. The upper and middle panels show the schematics and photographs of the light-responsive actuation of a hydrogel consisting of titanate nanosheets aligned orthogonally to the cylindrical gel axis and light-absorbing Au nanoparticles. The hydrogel undergoes peristaltic crawling and moves oppositely toward the laser scanning direction when the irradiation spot is moved along the cylindrical gel axis, as shown in the photographs (bottom panel). Reprinted with permission from ref (598). Copyright 2018 Wiley-VCH.