GEISLER, B.; DITTMORE, A.; GALLERY, B.; STRATTON, T.; FEARING, R.; AUTUMN, K.*; Lewis & Clark College; Lewis & Clark College; Lewis & Clark College; Lewis & Clark College; Univ. of California, Berkeley; Lewis & Clark College; ; : Deformation of isolated gecko setal arrays: bending or buckling? 2. Kinetics.

Conventional pressure sensitive adhesives (PSAs) are fabricated from soft viscoelastic materials that satisfy Dahlquist�s criterion for tack with a Young�s modulus, E, of 100 kPa or less. In contrast, the adhesive on the toes of geckos is made of &beta-keratin, a stiff material with E four to five orders of magnitude greater than the upper limit of Dahlquist�s criterion. Therefore, one would not expect a &beta-keratin structure to function as a PSA by readily deforming to make intimate molecular contact with a variety of surface profiles. However, since the gecko adhesive is a microstructure in the form of an array of millions of high aspect ratio shafts (setae) the effective elastic modulus, E_eff, is much lower than E of &beta-keratin. We measured the forces resulting from deformation of isolated arrays of Tokay gecko (Gekko gecko) setae as the first test of the E_eff of a gecko setal adhesive. We tested the hypothesis that E_eff of gecko setae falls within Dahlquist�s criterion for tack, and tested competing constitutive models of setae as either bending beams or buckling columns. Our results support a model of beam bending and contradict a model of buckling.