An optimised tapered shape of the terminal contact elements in biological attachment devices

Many biological attachment devices of insects, spiders and geckoes consist of arrays of hairs (setae), which are terminated by contact elements of different shapes. However, the most frequently observed shape is a thin plate-like spatula. In spite of a rather wide range of sizes and thicknesses, most spatulae of different animals are not uniform but possess a gradient in thickness. The thickness of spatulae in the longitudinal section becomes gradually thinner close to the tip. This geometrical effect is numerically explained in the present paper, by using a numerical approach for modeling the van der Waals-like adhesion and friction between the contact element and the substrate. The approach suggests that the observed tapering in the thickness is useful for improving resistance to peeling. Similarly, the existing complementary tapering in the spatula width increases the strength of the detachment process.