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zq17 vol 3 | 2016

Case Study Sticking to the Chase

with bristles or setae and each seta was divided at the tip; each tip division having a tiny spatula shaped pad. However, the precise molecular mechanism of adhesion remained unclear. Autumn believed that these nanoscale structures were enabling the gecko to stick to surfaces by van der Waals forces, weak molecular attraction, that, when aggregated over many tiny surface structures, could be sufficient to keep the gecko firmly planted, upside down, onto the ceiling of his Hawaiian bungalow. In 1997 the Full lab began its investigation of the gecko’s adhesive action by using high-speed cameras and force meters to understand the dynamics of how geckos climb. This combination of the elements of time and force was an important approach for studying complex actions that take place in a fraction of a second.

Author: Tom McKeag

ies in diameter, but is typically 40-50 microns in diameter, or about ten times the width of the typical seta. Despite weeks of painstaking work (particularly by Tonia Hseih, an undergraduate at Berkeley, now on the faculty at Temple University), the team could not get the single seta to stick to a metal insect pin, until it was discovered that it was the way that the seta was applied to the pin that mattered. “We already had the dynamics data, but didn’t realize they could help us make the single seta stick. It took us over a month to figure out that we needed to replicate the force pattern of a gecko foot to make the seta adhere.”, says Autumn who in the same year moved from Berkeley to his current lab at Lewis and Clark.

The same geometry discovered for the foot By 1998, the team was also investigating the in- applied to the individual setae: they must be dividual hair or seta on the foot of a tokay gecko. preloaded and dragged at 30 degrees in order to What was the mechanism of attachment at this grip. “Frictional Adhesion” was thus explained scale? Just measuring this was a challenge as as a result of applying a load force at a particular the setae are typically about 110 microns long angle. Since this force was directional or anisoand 4.2 microns in diameter. A human hair var- tropic, it increased the growing confidence that this was a material and geometry phenomenon.

Montage of 5 cryo-SEM images of a single seta of a tokay gecko (Gekko gecko). Photo: Kellar Autumn

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zq17 (zygote quarterly)  

ZQ: Our mission is to establish a credible platform showcasing the nexus of science and design in the field of biologically inspired design,...

zq17 (zygote quarterly)  

ZQ: Our mission is to establish a credible platform showcasing the nexus of science and design in the field of biologically inspired design,...