S1-3.4 Jan. 5 Frictional Adhesion of Natural and Synthetic Gecko Setal Arrays AUTUMN, K*; GRAVISH, N; WILKINSON, M; SANTOS, D; SPENKO, M; CUTKOSKY, M; Lewis & Clark College; Lewis & Clark College; Lewis & Clark College; Stanford University; Stanford University; Stanford University firstname.lastname@example.org
Gecko toes are adhesive only when dragged in shear away from their tips. This is due to the anisotropic function of the arrays of angled foot hairs (setae) that comprise the gecko adhesive. We measured 2D dynamics of bonding and de-bonding in isolated gecko setal arrays and the toes of live geckos. We found that adhesion depended directly on shear force (friction), consistent with previous results showing that single setae detach at a critical angle A* = 30°. We proposed a new model, frictional adhesion, for the function of gecko-like adhesives. In the non-adhesive direction, the Coulomb law governs friction: Fnormal >= -1/µ Fshear. In the adhesive direction, the adhesive force is limited by the shear force and A*, Fshear >= - Fnormal ÷ tanA*, which defines the minimum shear load to withstand a given adhesive load. This explains why geckos use opposing feet and toes to maintain shear forces that prevent detachment, and informs the design of synthetic gecko-like adhesives. We compared the new frictional adhesion model with the JKR and Kendall models of adhesive contact. The loading constraints predicted by the contact models lead to different force control strategies during attachment and detachment to prevent unwanted slippage and minimize foot detachment forces in a model gecko. We then fabricated arrays of synthetic anisotropic elastomeric microstructures. The 2D dynamics of the synthetic arrays were consistent with the frictional adhesion model, and enhanced the ability of a gecko-like climbing robot to scale a smooth vertical surface. We suggest frictional adhesion as a key benchmark for the performance of gecko-like synthetic adhesive structures. Support: DARPA N66001-03-C-8045, NSF-NIRT 0304730, DCI/NGIA HM1582-05-2022, Emhart, and J&J Dupuy-Mitek.