Geckos have fascinated naturalists since they were first discovered, thanks to the unique structure of their feet that allows them to crawl up flat surfaces. Dr. Kellar Autumn, chair of the Biology Department at Lewis and Clark College, has dedicated his career to understanding this adaptation and how it works. In a paper published this week in the Proceedings of the Royal Society, Dr. Autumn and colleagues present a new way of looking not only at gecko biomechanics, but the study of friction as a whole.
The paper is titled “Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition” and is available online here (Abstract is free, article with institutional subscription). Dr. Autumn’s co-authors include two other Lewis and Clark staff members, Dr. Jon Puthoff and Matt Wilkinson, as well as Peter Loskill from Saarland University and Klaus Mecke from Universität Erlangen-Nürnberg, both located in Germany.
I asked Dr. Autumn for a synopsis of the paper, and this was his answer:
By using gecko foot hairs as a probe, we discovered something new about friction. What lies below the surface can be as or even more important than the topmost layer of atoms.
There’s an impressive phrase you don’t see very often, even for those of us who spend our time combing through scientific papers – “we discovered something new about friction.”
Dr. Autumn also provided a slightly longer and more detailed explanation:
Surface energies are commonly used to predict adhesive forces between materials. We used gecko setae to test the hypothesis that the energy of atoms below the surface significantly influences forces between solids. We discovered that nanoscale differences in oxide thickness of semiconductors caused macroscale differences in adhesion. Variation in oxide layer thickness caused very subtle differences in the subsurface energy-distance relationship, but which significantly affected the force of adhesion. Our results challenge the conventional assumption that surface energy alone determines adhesion. We proposed a new term, ‘subsurface energy’, which may now be of importance in physics, biology, and engineering.
To learn more about Dr. Autumn’s lab and their ongoing gecko research, check out their lab website.
Photo courtesy of Bjørn Christian Tørrissen and Wikimedia Commons.