Fig. 1. Structure and friction performance of the attachment pads of the Chinese bush cricket (G. gratiosa, Tettigoniidae) and tree frog (Polypedates and Rhacophorus dennysi).

(A) A photo of a bush cricket crawling on a slippery glass. (B and C) One pair of attachment pads with surface composed of tightly packed hexagonal epithelial cells had a diameter, height, and channel width of about 5, 2, and 0.2 μm, respectively. Magnified epithelial cells show a smooth outer layer. (D) Section view of the pad after critical point drying shows that the branched fibrous structures extend from ~100-μm depth in the cuticle to the top surface of the hexagonal pillar. The inset shows that the diameter of the root fiber is ~1 μm. (E) The hexagonal pillars are embedded inside with tiny fibers that are dispersed from the root fibers and have a diameter of ~100 nm. (F) Section view of the epithelial cell from the tree frog’s toe pad shows homogeneous pillar structures. (G) The interfacial secretion film states of cricket’s and tree frog’s pads during repeated sliding process. The dark areas denote the interfacial secretion film at contact interface. The yellow dashed circles indicate the individual epithelial cells, and the yellow arrows indicate the positions where interference fringes appear, representing the separation of cells and glass substrate. (H) The shear stress of cricket’s and tree frog’s pads during repeated sliding process. All friction tests are measured with a normal load of ~1 kPa and a contact area of ~1 mm².