My primary interest is in the evolution and function of adhesive feet, specifically *dry* adhesive feet such as those possessed by spiders and geckos. These operate by van der Waals interactions so that sticking is as easy as touch and go!

How do geckos make use of the smallest of intermolecular forces to climb walls? Tiny hairs derived from the keratin in the skin on their feet create a large, compliant surface area which makes intimate contact with the substrate. One Tokay gecko (Gekko gecko) may possess several millions of these hairs, called setae. Each seta is in turn subdivided into 100-1000 smaller flattened tips, called spatulae (see figure below).

Why van der Waals? Although they are the weakest type of intermolecular force, they are ubiquitous and occur between all types of surfaces. This means that the key to dry adhesion is the shape or geometry of the adhesive, rather than the chemistry. Other insects which stick by secretions (e.g. ants, beetles, flies, etc.) are much more picky about what types of surfaces they stick to. Geckos can stick to any surface, with the exception of Teflon, which was specifically engineered to prevent even van der Waals adhesion. (You might say that Teflon is the Anti-Gecko.)

Dry adhesives such as these have evolved independently multiple times within gekkonid lizards, as well as in anoles, skinks, and multiple times again in spiders. This highly diverse set of organisms allows us to conduct statistically powerful comparative studies to determine how adhesive feet evolved and what benefits they confer on the animals which possess them.

I started working on gecko adhesion as an undergraduate in Kellar Autumn's lab at Lewis & Clark College (Portland, OR). Other collaborators on the gecko project include Ronald S. Fearing in the Dept. Electrical Engineering and Computer Science here at UC Berkeley, Anthony Russell at University of Calgary, Jacob Israelachvili at UC Santa Barbara, and Thomas W. Kenny in the Mechanical Engineering Dept. at Stanford University.

Ron Fearing's lab is part of an exciting effort to synthesize artificial gecko adhesives. I have worked with members of his lab, including Carmel Majidi, Rick Groff and former postdoc Metin Sitti in a mutually beneficial interdisciplinary collaboration towards this end. Once we fabricate a physical model of gecko foot-hairs, we can use it as an independent line of evidence to test our hypotheses of adhesive function in the organisms.