AUTUMN, K.*; HANSEN, W.R.; Lewis & Clark College, Portland OR: Gecko setae: a self-cleaning adhesive nanostructure

The adhesive nanostructure on the gecko foot sets the benchmark for the smart adhesives of the future. No other adhesive requires near-zero attachment force, is directional, detaches easily, leaves no residue, and works underwater, in a vacuum, and on nearly every surface material and profile. Previously, we discovered that gecko setae stick by van der Waals forces, implying that adhesion is a function of geometry of the nanostructure rather than its surface chemistry. A single seta can hold 20 mg and a gecko�s worth of setae (~6.5 million) could theoretically support 130 kg. The remarkable adhesive capacity of gecko setae raises the question of why such a sticky adhesive does not become rapidly inactivated by dirt during locomotion. The Tokay (Gekko gecko) is not known to groom its feet yet maintains adhesive function during many thousands of adhesion-detachment cycles during the months between skin molts. We hypothesized that setae are susceptible to particulate contamination, but that passive self-cleaning is an intrinsic property. If this is correct, gecko setae are the first self-cleaning adhesive known to science. We tested the self-cleaning hypothesis by measuring 1) shear force of the toes of live Tokays adhering to glass before and after contamination with 2.5 micron ceramic microspheres. 2) shear force of isolated setal arrays under the same conditions. Isolating adhesive setal arrays controlled for cleaning by grooming or movement of feet or toes. Contamination significantly reduced adhesive function in live and isolated setae. However, after several simulated steps on glass, adhesive function increased rapidly. Electron microscopy revealed a corresponding decrease in microsphere attachment to setal tips. Self-cleaning occurred in live setae and in setae apart from the gecko, supporting the hypothesis that elimination of particles is an intrinsic property of the gecko adhesive.