Meeting Abstract

S4.3  Monday, Jan. 5  Convergent evolution of hairy attachment devices GORB, Stanislav N.; Zoological Institute, Department of Zoology: Functional Morphology and Biomechanics, University of Kiel, Kiel, Germany s.gorb@mf.mpg.de

Most recent data on biological hairy attachment systems demonstrated their excellent adhesion and high reliability of contact. In contrast to smooth systems (tree frogs, grasshoppers), some hairy systems (geckos, spiders) seem to operate because of dry adhesion, because they do not produce supplementary fluids in the contact area. Interestingly, hairy systems appeared several times in animal evolution and at least three times independently even within insect evolution. This fact may indicate that such surfaces must have an advantage for adhesion enhancement in biological systems and also in artificial surfaces with similar geometries. The physical background of this effect was theoretically discussed in several recent publications. Comparison of the wide variety of animal groups revealed that the size of single contacting points gets smaller and their density increases as the body mass increases. This general trend is theoretically explained by applying the JKR theory, according to which splitting up the contact into finer sub-contacts increases adhesion. The effective elastic moduli of the fiber arrays and spatula-like terminal elements are very small, which is of fundamental importance for adhesion on rough substrata. It is predicted that an additional advantage of patterned surfaces is the reliability of contact on various surface profiles and the increased tolerance of defects at individual contacts. In a real situation, failure of some microcontacts due to dust particles or to mechanical damage of single seta would minimally influence adhesion. In the case of a solitary contact, even slight damage of the contact due to the presence of dirt or surface irregularities will immediately lead to contact breakage similar to the crack propagation in bulk material.