Effect of Variation in Length and Width on Single Seta Force in Geckos

Meeting Abstract

42.1  Saturday, Jan. 5  Effect of Variation in Length and Width on Single Seta Force in Geckos PEATTIE, AM*; FULL, RJ; Univ. of California, Berkeley; Univ. of California, Berkeley apeattie@berkeley.edu

Adhesive structures on gecko feet exhibit considerable morphological variation. To test the effect of this variation on adhesive performance, we measured single-seta force in eight species of broad phylogenetic distribution. We attached setae to a smooth silicon surface fixed to a wire functioning as a cantilever force gauge. We collected high-speed video of each trial to determine the shear and normal adhesives forces, as well as critical detachment angle during normal pull-offs. The van der Waals hypothesis of gecko adhesion predicts that an increased number of branched tips (�spatulae�) should lead to an increased adhesive force. Shear force increased significantly with the number of spatulae to the 0.78 power (r2=0.62), as did pull-off force (0.63; r2=0.25). Since number of spatulae per seta was positively correlated with seta width (r2=0.71), there were corresponding increases in shear (1.7; r2=0.47) and pull-off force (1.2; r2=0.15) with width. Due to a strong correlation between seta width and length, we expected a similar correlation between seta length and adhesive force. We found a significant relationship, but with lower correlation in both shear (0.78; r2=0.14) and pull-off directions (0.42; r2=0.03), suggesting that variation in length has less consequence for adhesive performance on smooth surfaces. Length is predicted to have an important effect on rough substrates. Research groups currently modeling gecko setae mathematically, as well as physically by fabrication, should consider the effect of morphological variation on performance. Future evolutionary analyses will assist in the identification of key functional parameters amongst the diversity of setae in nature. Funded by NSF NIRT.

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