Elasto-capillarity in insect fibrillar adhesion

Abstract

The manipulation of microscopic objects is challenging because of high adhesion forces, which render macroscopic gripping strategies unsuitable. Adhesive footpads of climbing insects could reveal principles relevant for micro-grippers, as they are able to attach and detach rapidly during locomotion. However, the underlying mechanisms are still not fully understood. In this work, we characterize the geometry and contact formation of the adhesive setae of dock beetles (Gastrophysa viridula) by interference reflection microscopy. We compare our experimental results to the model of an elastic beam loaded with capillary forces. Fitting the model to experimental data yielded not only estimates for seta adhesion and compliance in agreement with previous direct measurements, but also previously unknown parameters such as the volume of the fluid meniscus and the bending stiffness of the tip. In addition to confirming the primary role of surface tension for insect adhesion, our investigation reveals marked differences in geometry and compliance between the three main kinds of seta tips in leaf beetles.

Elastocapillarity: When Surface Tension Deforms Elastic Solids

“…The barbules of bird feathers may for instance form fatal clumps when contaminated by oil (Duprat et al, 2012). At a smaller scale, the adhesive setae from some insect species may also form bundles (Gernay et al, 2016).…”

Rupture of a Liquid Bridge between a Cone and a Plane

“…For example, beetles possess hairy pads and secrete some liquid at the tip of each hair to form temporary bridges with the substrate. [8][9][10][11] Liquid bridges are therefore ubiquitous in nature. 12 The trend to miniaturization requires to handle even smaller micro-components: they must be picked, placed with high accuracy and then released.…”

“…The handling of micro-components may take advantage of surface tension forces, which usually dominate body forces at this scale. 9 For example, capillary grippers use the capillary forces generated by a liquid meniscus between the gripper and the component. 1,[13][14][15] This gripping principle exhibits many advantages.…”

Inter‐ and intraspecific differences in leaf beetle attachment on rigid and compliant substrates

“…While the multifactorial influences of rigid substrates on insect attachment is well understood (e.g. Stork, ; Gorb, Gorb & Kastner, ; Betz, ; Voigt, Gorb & Gorb, ; Voigt et al ., , ; Gernay et al ., ), compliant substrates have been largely neglected so far. However, material properties of substrates are as diverse as their surface topography (e.g.…”

“…Both the structure and performance of tarsal attachment devices in these beetle species are well described (e.g. Peressadko & Gorb, ; Schuppert et al ., ; Voigt et al ., , ; Bullock & Federle, , ; Gorb & Gorb, ; Clemente et al ., ; Hosoda & Gorb, ; Prüm et al ., ; Gernay et al ., , ; Zurek, Gorb & Voigt, ). Both species bear similar spatula‐shaped, lanceolate and filament‐shaped tarsal adhesive setae in males (♂♂) and females (♀♀), and additional setae with discoid terminal tips present only in males (Stork, ; Pelletier & Smilowitz, ) (Fig.…”