From micro to nano contacts in biological attachment devices

doi:10.1073/pnas.1534701100

From micro to nano contacts in biological attachment devices

^†Max Planck Institute for Metals Research, Heisenbergstrasse 3, 70569 Stuttgart, Germany; and ^§Biological Microtribology Group, Max Planck Institute of Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany

Communicated by Walter L. Brown, Lehigh University, Bethlehem, PA, July 25, 2003 (received for review December 19, 2002)

Abstract

Animals with widely varying body weight, such as flies, spiders, and geckos, can adhere to and move along vertical walls and even ceilings. This ability is caused by very efficient attachment mechanisms in which patterned surface structures interact with the profile of the substrate. An extensive microscopic study has shown a strong inverse scaling effect in these attachment devices. Whereas μm dimensions of the terminal elements of the setae are sufficient for flies and beetles, geckos must resort to sub-μm devices to ensure adhesion. This general trend is quantitatively explained by applying the principles of contact mechanics, according to which splitting up the contact into finer subcontacts increases adhesion. This principle is widely spread in design of natural adhesive systems and may also be transferred into practical applications.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: arzt{at}mf.mpg.de.
↵ ¶ Electron microscopy and data analysis were performed as follows. Animals were fixed in 70% ethanol. Some pieces of materials were dehydrated in ethanol and critical-point dried. Pieces of the material were fractured with a razor blade. All preparations were critical-point dried, mounted on holders, sputter-coated with gold-palladium (10 nm), and examined in a Hitachi S-800 scanning electron microscope at 20 kV. Measurements of structures were made on digital pictures with analysis 2.1 image analysis software (Soft-Imaging Software, Münster, Germany).
↵ ∥ The following animals with attachment devices were used for analysis: spiders (Cupiennius salei, and Aphonopelma seemanni), insects (Calliphora erythrocephala, Drosophila melanogaster, Lucilia caesar, Platycheirus angustatus, Sphaerophoria scripta, Episyrpus balteatus, Eristalis pertinax, Myathropa florea, Volucella pellucens, Cantharis fusca, Leptinotarsa decemlineata, Gastrophysa viridula, Chrysolina fastuosa, Phyllobius pomaceus, and Rhodnius prolixus), and geckos (Tarentola mauritanica, Phelsuma madagascariensis, Tarentola mauritanica, Anolis maynardi, and Gecko gekko).