(a) Crawler with zoomed-view of fibers in the feet. Reprinted with permission from Ref. [13]. Copyright 2006, IEEE. (b) Centipede-like microrobot. Reprinted with permission from Ref. [37]. Copyright 2011, Springer. (c) HAMR2. Reprinted with permission from Ref. [35]. Copyright 2010, IEEE. (d) Top-view and (e) bottom-view of HAMR3. Reprinted with permission from Ref. [36]. Copyright 2011, IEEE. (f) Centipede millirobot. Reprinted with permission from Ref. [14]. Copyright 2013, IEEE. (g) HAMR-VP. Reprinted with permission from Ref. [39]. Copyright 2014, SAGE. (h) MinRAR. Reprinted with permission from Ref. [40]. Copyright 2017, IEEE.