(a) Field-effect transistors based on Ge/Si NW arrays with different channel widths that can be printed on flexible substrates. (Reprinted with permission from Fan et al. [261]. Copyright 2009 by Wiley.) (b) A 3D coiled Si NW (due to buckling) under stretching. (Reprinted with permission from Xu et al. [245]. Copyright 2011 by American Chemical Society.) (c) Resistance as a function of applied strain during loading, unloading, and reloading (left) and the schematic of the corresponding mechanism. (Reprinted with permission from Xu and Zhu [12]. Copyright 2012 by Wiley.) (d) A pressure sensor array. (Reprinted with permission from Yao and Zhu [246]. Copyright 2014 by Royal Society of Chemistry).