Figure 1. Structure and dynamic adhesive force of gecko setae and spatulae.

(a) Optical image of a gecko sole. SEM images of (b) setal array (scale bar, 20 μm) and (c) a single spatula (isolated from a seta) glued onto a tipless AFM cantilever (scale bar, 20 μm; inset, 500 nm). Adhesive forces of the single spatula on mica, FS and PS substrates versus (d) pull-off velocity (V_n) and (e) shear velocity (V_s) for a preload of 10 nN and a drag distance of 4 μm. (f) SEM images of a single seta glued on a tipless AFM cantilever(scale bar, 30 μm). (g) Adhesive forces of the single seta on mica, FS and PS substrates as a function of the pull-off velocity at given shear velocities of V_s=0.1 and 1,000 μm s⁻¹ for a preload of 1 μN, and a drag distance of 4 μm (inset: the schematic of a single seta in making contact with a substrate). (h) Adhesive forces of a SiO₂ microsphere (diameter, d=10 μm) adhered to a seta as a function of the pull-off velocity for a preload of 1 μN and a drag distance of 1 μm (inset: the schematic of microsphere-seta complex, in making contact with fused silica substrate). All the tests are performed in air with a relative humidity of 21% at room temperature.