RUI: Comparative micromechanics of gecko setae: Effects of rate, substrate, and environment

Lewis And Clark College, Portland OR

Investigators

Abstract

Gecko toe pads are sticky because they bear a hierarchy of structure that functions as a smart adhesive. The adhesive on gecko toes differs dramatically from that of conventional pressure-sensitive adhesives (PSAs), which are soft polymers that degrade, foul, self-adhere, and attach accidentally to inappropriate surfaces. In contrast, gecko toes bear angled arrays of branched, hair-like fibers (setae) formed from stiff, hydrophobic keratin that act as a bed of angled springs with an effective stiffness similar to that of PSAs. Setae are self-cleaning and maintain function for months during repeated use in dirty conditions. Adhesion in setae requires maintenance of a shear load directed toward the body of the gecko. Thus, gecko setae resist inappropriate bonding and are capable of easy and rapid attachment and detachment. Prior research is based predominately on data collected from a single species, the tokay gecko, on smooth surfaces at ambient relative humidity. Functionally, the diversity of setal designs in over 1000 species of gecko is not well understood. Also, theory and data conflict with regard to the effects of van der Waals forces and humidity on gecko adhesion. These are topics of central importance in understanding the mechanisms of gecko adhesion and in the design and application of gecko-like synthetic adhesives (GSAs). This project focuses on identifying general, testable principles underlying the novel attachment system that geckos use to climb. It will test the validity of four theoretical models of setal structure and function by measuring material properties and contact mechanics of a diverse sample of gecko setae, and by utilizing GSAs as physical models. The project will tease apart the effect of humidity and temperature on keratin mechanical properties from the effect of surface hydration by measuring changes in stiffness and frictional adhesion as a function of humidity, temperature, and substrate hydrophobicity. The research will advance understanding of the micromechanics of gecko setae under a range of biologically relevant environmental conditions, enabling transformative advances in adhesion technology and the physics of friction. Engineered adhesive nanostructures inspired by geckos may become the glue of the future and perhaps the screw of the future as well.