Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour

Abstract

The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 mm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.

Ultrastructure and physical properties of an adhesive surface, the toe pad epithelium of the tree frog, Litoria caerulea White

“…Lee et al, 2007;Lee et al, 2008;Schubert et al, 2008), it is appropriate to consider whether the rather different wet adhesion mechanism of tree frogs might also have biomimetic relevance. An obvious possibility is the development of improved wet weather tyres (Barnes, 1999;Barnes et al, 2002;Persson, 2007).…”

Optimal Angles for Maximal Adhesion in Living Tokay Geckos

“…Such open questions include function, molecular mechanism, morphological characteristics of the nano-hierarchical structures, mechanism of frictional adhesion, tail function during climbing or aerial descent, and interactive effects of size and loading on kinematics. The milli seconds controllable attachment=detachment mechanism in geckos with negligible forces assumed a huge importance also from a technological point of view, e.g., fabrication of dry adhesives, robotics systems, artificial adhesive suits, and gloves for astronauts [21,23,30,[35][36][37][38][39][40][41]; this is achieved thanks to the uniqueness of the gecko adhesive system in terms of repeatable strong foot contacts combined with temporary and reversible weak bonds, basically intermolecular van der Waals forces [14,30,33,[42][43][44]. In order to maintain the necessary shear=frictional adhesive [12] forces and to avoid toe detachment, the gecko adhesive mechanism is based on the use of opposing feet and toes making a V-shaped geometry and the gecko attachment being achieved only proximally along the toe axis of the gecko, which pulls its feet inwards towards the center of mass (COM) and its toes inwards towards the foot to engage adhesion [14,21,30,31,34,45,46], as schematically reported in Fig.…”

Comparison of smooth and hairy attachment pads in insects: friction,adhesion and mechanisms for direction-dependence

“…Fibrillar adhesive systems have recently attracted much attention from the engineering and physical sciences because they are considered to be promising models for novel, biomimetic adhesives (Aksak et al, 2007;Glassmaker et al, 2004;Gorb et al, 2007;Hui et al, 2004;Jagota et al, 2007;Kim and Sitti, 2006;Lee et al, 2008;Menon and Sitti, 2006;Schubert et al, 2008). The fibrillar design is thought to convey a number of specific advantages, such as superior performance on rough substrates (Persson and Gorb, 2003), effortless detachment (Autumn and Hansen, 2006;Autumn et al, 2006a;Autumn et al, 2006b;Federle, 2006), self-cleaning properties (Hansen and Autumn, 2005) and increased adhesion due to contact splitting (Arzt et al, 2003).…”