title: Insect adhesion on rough surfaces: analysis of adhesive contact of smooth and hairy pads on transparent microstructured substrates.
abstract: Insect climbing footpads are able to adhere to rough surfaces, but the details of this capability are still unclear. To overcome experimental limitations of randomly rough, opaque surfaces, we fabricated transparent test substrates containing square arrays of 1.4 µm diameter pillars, with variable height (0.5 and 1.4 µm) and spacing (from 3 to 22 µm). Smooth pads of cockroaches (Nauphoeta cinerea) made partial contact (limited to the tops of the structures) for the two densest arrays of tall pillars, but full contact (touching the substrate in between pillars) for larger spacings. The transition from partial to full contact was accompanied by a sharp increase in shear forces. Tests on hairy pads of dock beetles (Gastrophysa viridula) showed that setae adhered between pillars for larger spacings, but pads were equally unable to make full contact on the densest arrays. The beetles' shear forces similarly decreased for denser arrays, but also for short pillars and with a more gradual transition. These observations can be explained by simple contact models derived for soft uniform materials (smooth pads) or thin flat plates (hairy-pad spatulae). Our results show that microstructured substrates are powerful tools to reveal adaptations of natural adhesives for rough surfaces.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
authors.forename: Yanmin
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
authors.forename: Adam
authors.initials: A
authors.lastname: Robinson
authors.affiliation: Department of Physics, Nanoscience Centre, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Ullrich
authors.initials: U
authors.lastname: Steiner
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK wf222@cam.ac.uk.
authors.forename: Walter
authors.initials: W
authors.lastname: Federle
mesh_terms: D000268:Adhesiveness; D000818:Animals; D001696:Biomechanical Phenomena; D003058:Cockroaches / Q000502:physiology*; D001517:Coleoptera / Q000502:physiology*; D005121:Extremities / Q000502:physiology*; D007313:Insecta; D008124:Locomotion; D008855:Microscopy, Electron, Scanning; D033081:Shear Strength
keywords: adhesion; biomechanics; contact mechanics; photolithography; surface roughness; tribology