Various motion control methods of hydrogel micromotors. (a) Velocity control of PNIPAM-modified stomatocyte hydrogel micromotors using thermosensitive PNIPAM hydrogel. Reproduced with permission from ref. [65
], Springer 2017. (b) Activation of PNIPAM-Pt hydrogel micromotors by bubbles during reversible rolling of layers at different temperatures (I)~(II) (scale bars: 50 μ
m). Reproduced with permission from ref. [80
], Wiley-VCH 2014. (c) Direction control by enclosing SPION magnetic nanoparticles in the hydrogel matrix and in a magnetic field. Reproduced with permission from ref. [72
], EU 2015.