Fig. 1.

The principles of gecko adhesion. (a) (i) Picture of a Tokay gecko sticking to an acrylic glass with the background showing the top part of a single seta; (ii) confocal laser microscope (CLSM) image of single gecko seta, showing an overlay image of three different autofluorescence of (iii)–(v). The overall colors become more intense from the base to the tip (i.e., from left to right in (ii)), suggesting an increasing amount of β-keratin from the base to the tips. Therefore, a gradient density distribution exists along the seta, consequently causing a gradient in mechanical properties. (iii)–(v) CLSM images of seta with single excitation wavelengths of 458, 561, and 633 ​nm, respectively. (b) Schematic of the AFM nanoindentation tests of single gecko seta at different setal stalk positions. (c) Calculated gradient distribution of Young's modulus of the single seta based on the AFM force curve obtained at varied longitudinal positions. (d) NMR spectroscopy reveals the presence and association of lipids and keratin in adhesive gecko setae. (e) SEM image of the gecko lamellar skin. (f) Schematic of the bending/conforming mechanism of gecko setae and lamellae during attachment [[41], [43]].