S1-3.5 Jan. 5 Work of Detachment is Controllable in Gecko Setal Arrays GRAVISH, N*; WILKINSON, M; AUTUMN, K; Lewis & Clark College; Lewis & Clark College; Lewis & Clark College email@example.com
Gecko setae are anisotropic in adhesive function. Comprised of thousands of angled hairs, setal arrays attach strongly when dragged along their natural curvature. Dragging against curvature produces low friction and no adhesion. We discovered that the mechanical work of detachment in the normal axis (Gn) for setal arrays is anisotropic, likely as a consequence of setal structure. Previously we found that house geckos (Hemidactylus garnotii) running vertically detached their feet in 15 ms without measurable effects on center of mass kinetic energy. This suggests that the work to detach a setal array can be quite low. We measured the dynamics of detachment in isolated tokay gecko (Gekko gecko) setal arrays to determine Gn at angles of 30° to 150°. A detachment vector pointing away from and normal to the substrate corresponds to an angle of 90°, and 0° is parallel to the surface, in the direction of natural setal curvature. For angles below 120°, Gn was constant and more than three orders of magnitude greater than the thermodynamic interfacial energy predicted for van der Waals forces. This suggests that energy is lost internally to the setal array, greatly increasing Gn. For detachment angles above 120°, Gn became negative indicating that elastic energy from setal compression was released. Energetically optimal detachment paths occurred at angles above 120°. Thus the easiest method for a gecko to detach its toes may be a small push away from the body. The control of adhesive energy through modulation of the applied force vector has utility in the design of climbing robots and setal adhesives. A simple angled rigid beam model of the seta predicts anisotropy in Gn suggesting that this property will be replicable in synthetic adhesive microstructures. Support: DARPA N66001-03-C-8045, NSF-NIRT 0304730, DCI/NGIA HM1582-05-2022, Emhart, J&J Dupuy-Mitek.