Getting a grip on spider attachment: an AFM approach to microstructure adhesion in arthropods

Abstract

Although the spider exoskeleton, like those of all other arthropods (spiders, insects and crustaceans), consists of an extremely non-adhesive material known as cuticle, some spider species produce astonishingly high adhesive forces using cuticular appendages. Unlike other arthropods, they do not rely on sticky fluids but use a different strategy: the miniaturization and multiplication of contact elements. In this study the number of contact elements (setules) in the species Evarcha arcuata was determined at 624 000 with an average contact area of 1.7 × 105 nm2. The total area of contact in this species measured 1.06 × 1011 nm2. By using atomic force microscopy it was shown that a single setule can produce an adhesive force of 41 nN perpendicular to a surface. Thus with a total adhesive force Fa = 2.56 × 10−2 N and an average body mass of 15.1 mg, this species possesses a safety factor (adhesive force Fa/force for weight Fm) of 173. The tenacity σ (ultimate tensile strength) amounts to 0.24 MPa. Due to the extreme miniaturization of the contact elements it is assumed that van der Waals forces are the underlying adhesive forces, although final evidence for this has yet to be provided. The present study was performed in order to clarify the fundamental basics of a biological attachment system and to supply potential input for the development of novel technical devices.

Dynamic self-cleaning in gecko setae via digital hyperextension

“…Such a high adhesion force at the microscale will lead to setal jumping off during toe pad scrolling. This jump-off event is a common phenomenon that has been observed in many other systems such as atomic force microscope pull-off tests for measuring micro-/nano-adhesion [25,[27][28][29][30][31] and single carbon nanotube peeling tests [32,33].…”

Tarantulas cling to smooth vertical surfaces by secreting silk from their feet

“…Usually, when spiders adhere to smooth vertical surfaces they use pads of finely divided hairs (setae) on the underside of their tarsi (Kesel et al, 2003;Niedregger and Gorb, 2006;Artz et al, 2003;Roscoe and Walker, 1991;Gasparetto et al, 2009); this type of dry adhesion relies on the intra-molecular forces set up between the tips of the hairs and the substrate (Kesel et al, 2003;Niedregger and Gorb, 2006;Artz et al, 2003;Kesel et al, 2004;Roscoe and Walker, 1991;Gasparetto et al, 2009). These pads are known as scopula pads and occur on the tarsi and meta-tarsi of all legs including the pedipalps in female spiders.…”

Observations of shear adhesive force and friction of Blatta orientalis on different surfaces

“…Many authors have studied a multitude of insects, especially thanks to the availability of microscopic analysis instruments (Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM)), in order to understand and measure their adhesive abilities; in the course of the last decades, beetles [1][2][3][4][5][6], aphids [8][9][10], flies [7,11,12], bugs [13], ants [14][15][16][17], cockroaches [18][19][20][21][22][23][24], spiders [25][26][27] and geckos [28][29][30][31][32][33][34][35][36][37][38] have been extensively studied.…”

“…claws, clamp, sucker, glue, friction), even if during evolution the insect attachment pads have evolved in two main types, which are hairy (thousands of flexible hairs, as fly pulvilli and beetle pads) or smooth (with high deformable material, as grasshoppers and cockroaches): both the systems are able to adapt to the substrata, maximizing the contact area [39][40][41]. For example, geckos present a dry adhesive surface, organized in a hierarchical structure [28,42], like anoles [35,43,44], skinks [35,45] and spiders [26,27]; while other animals present secretion-aided fibrillas or secretion-aided pads, which are common in some insects [46], like ants [15], cockroaches [18], mites [47] and beetles [48]. The adhesive organs of these insects consist in smooth pads and the adhesion is mediated by a few volume of fluid secreted into the contact zone that influences the attachment performance [49,50].…”