Meeting Abstract
42.2 Saturday, Jan. 5 Dynamic response to sliding in isolated gecko setal arrays GRAVISH, NICK*; WILKINSON, MATT; AUTUMN, KELLAR; Lewis & Clark College; Lewis & Clark College; Lewis & Clark College gravish@lclark.edu
Under most conditions, geckos adhere strongly and have no difficulty maintaining adhesive contact. Casual observations indicate that geckos can run on inverted surfaces and maintain adhesion even when their feet slip. However, even microscale slippage in conventional adhesive materials typically causes bond reduction leading to failure. This suggests that during sliding, the dynamics of adhesive contact in gecko setae differ from those of known systems. We investigated the effect of shear velocity on friction and adhesion in isolated tokay gecko setal arrays and discovered that unlike any known dry system, gecko setae adhere more strongly at greater sliding velocities. Over a shear velocity range of 6 orders of magnitude (500nm/s to 158mm/s) we found that below a critical velocity, vc = 0.158mm/s, forces were constant. Above vc, frictional-adhesion forces increased logarithmically: increasing shear velocity by 3 orders of magnitude above vc resulted in a 2.9x increase in friction (consistent with previous measurements; Sponberg et al., SICB 2001) and 7.9x increase in adhesion. Microscale slipping of a gecko�s adhesive may serve to strengthen contact forces during climbing and act as a passive stabilizing mechanism. While velocity-increased friction is typical in soft, deformable materials, it is surprising in a dry, hard keratin material. Thus the effect of velocity on friction and adhesion we observed is likely a result of setal geometry rather than the material properties of keratin protein. The effect of velocity on friction and adhesion in setae may result from population dynamics of individual stick-slip events at the spatular or setal scales. If so, it should be possible to fabricate synthetic setae with a similar dynamic response. These results highlight another unique property of the gecko adhesive, aptly suited to one of the world�s best climbers. Support: NSF-NIRT 0304730, DCI/NGIA HM1582-05-2022.
