Ultrahydrophobicity indicates a non-adhesive default state in gecko setae

Original Paper


Geckos may represent the world’s most demanding adhesives application. The adhesive setae on the toes of climbing geckos must adhere strongly yet avoid fouling or attachment at inappropriate times. We tested the hypothesis that gecko setae are non-adhesive in their unloaded default state by comparing the water droplet contact angle (θ) of isolated setal arrays to the smooth surface of eye spectacle scales of tokay geckos (Gekko gecko). At equilibrium, θ was 98.3 ± 3.4° in spectacle scales of live geckos and 93.3 ± 3.5° in isolated spectacles. Isolated setal arrays were ultrahydrophobic, with θ of 160.6 ± 1.3° (means ± SD). The difference in θ of setal arrays and smooth spectacles indicates a very low contact fraction. Using Cassie’s law of surface wettability, we infer that less than 6.6% of the surface of unloaded setae is solid and at least 93.4% is air space. We calculated that the contact fraction must increase from 6.6% in the unloaded state to 46% in the loaded state to account for previously measured values of adhesion. Thus gecko setae may be non-sticky by default because only a very small contact fraction is possible without mechanically deforming the setal array.


Adhesion Contact mechanics Locomotion Reptilia Nanotechnology 



Young’s modulus


Effective modulus


Fraction of surface area occupied by solid; contact fraction


Fraction of surface area occupied by air


Surface energy


Pressure sensitive adhesive




Water droplet contact angle


Equilibrium water droplet contact angle


Advancing water droplet contact angle


Receding water droplet contact angle


Adhesion energy


  1. Alibardi L (2003) Ultrastructural autoradiographic and immunocytochemical analysis of setae formation and keratinization in the digital pads of the gecko Hemidactylus turcicus (Gekkonidae, Reptilia). Tissue Cell 35:288–296PubMedCrossRefGoogle Scholar
  2. Arzt E, Enders S, Gorb S (2002) Towards a micromechanical understanding of biological surface devices. Z Metallkunde 93:345–351Google Scholar
  3. Arzt E, Gorb S, Spolenak R (2003) From micro to nano contacts in biological attachment devices. Proc Natl Acad Sci USA 100:10603–10606PubMedCrossRefGoogle Scholar
  4. Autumn K, Peattie A (2002) Mechanisms of adhesion in geckos. Integr Comp Biol 42:1081–1090CrossRefGoogle Scholar
  5. Autumn K, Liang YA, Hsieh ST, Zesch W, Chan W-P, Kenny WT, Fearing R, Full RJ (2000) Adhesive force of a single gecko foot-hair. Nature 405:681–685PubMedCrossRefGoogle Scholar
  6. Autumn K, Sitti M, Peattie A, Hansen W, Sponberg S, Liang YA, Kenny T, Fearing R, Israelachvili J, Full RJ (2002) Evidence for van der Waals adhesion in gecko setae. Proc Natl Acad Sci USA 99:12252–12256PubMedCrossRefGoogle Scholar
  7. Autumn K, Buehler M, Cutkosky M, Fearing R, Full RJ, Goldman D, Groff R, Provancher W, Rizzi AA, Saranli U, et al. (2005) Robotics in scansorial environments. Proc SPIE 5804:291–302Google Scholar
  8. Autumn K, Hsieh ST, Dudek DM, Chen J, Chitaphan C, Full RJ (2006) Dynamics of geckos running vertically. J Exp Biol 209:260–272PubMedCrossRefGoogle Scholar
  9. Baier RE, Shafrin EG, Zisman WA (1968) Adhesion: mechanisms that assist or impede it. Science 162:1360–1368PubMedCrossRefGoogle Scholar
  10. Barthlott W, Neinhuis C (1997) Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta 202:1–8CrossRefGoogle Scholar
  11. Barthlott W, Neinhuis C (1998) The lotus-effect: a paradigm for the use of a natural design for technical application. Am J Bot 85:6Google Scholar
  12. Baum C, Meyer W, Stelzer R, Fleischer L-G, Siebers D (2002) Average nanorough skin surface of the pilot whale (Globicephala melas, Delphinidae): considerations on the self-cleaning abilities based on nanoroughness. Mar Biol 140:653–657CrossRefGoogle Scholar
  13. Bereiter-Hahn J, Matoltsy AG, Richards KS (1984) Biology of the integument 2: vertebrates. Springer, Berlin Heidelberg New YorkGoogle Scholar
  14. Bonser RHC (2000) The Young’s modulus of ostrich claw keratin. J Mater Sci Lett 19:1039–1040CrossRefGoogle Scholar
  15. Bonser RHC, Purslow PP (1995) The Young’s modulus of feather keratin. J Exp Biol 198:1029–1033PubMedGoogle Scholar
  16. Cassie A, Baxter S (1944) Wettability of porous surfaces. Trans Faraday Soc 40:546–551CrossRefGoogle Scholar
  17. Chen W, Fadeev AY, Hsieh MC, Oner D, Youngblood J, McCarthy T (1999) Ultrahydrophobic and ultralyophobic surface: some comments and examples. Langmuir 15:3395–3399CrossRefGoogle Scholar
  18. Dahlquist CA (1969) Pressure-sensitive adhesives. In: Patrick RL (ed) Treatise on adhesion and adhesives, vol 2. Dekker, New York, pp. 219–260Google Scholar
  19. Dellit W-D (1934) Zur Anatomie und Physiologie der Geckozehe. Jena Z Naturw 68:613–656Google Scholar
  20. Fraser RDB, Parry DAD (1996) The molecular structure of reptilian keratin. Int J Biol Macromol 19:207–211PubMedCrossRefGoogle Scholar
  21. Gao X, Jiang L (2004) Water-repellent legs of water striders. Nature 432:36PubMedCrossRefGoogle Scholar
  22. Gay C, Leibler L (1999) Theory of tackiness. Phys Rev Lett 82:936–939CrossRefGoogle Scholar
  23. Geisler B, Dittmore A, Gallery B, Stratton T, Fearing R, Autumn K (2005) Deformation of isolated gecko setal arrays: bending or buckling? 2. Kinetics. Society of Integrative and Comparative Biology, San DiegoGoogle Scholar
  24. Hansen W, Autumn K (2005) Evidence for self-cleaning in gecko setae. Proc Natl Acad Sci USA 102:385–389PubMedCrossRefGoogle Scholar
  25. Hiller U (1968) Untersuchungen zum Feinbau und zur Funktion der Haftborsten von Reptilien. Z Morphol Tiere 62:307–362CrossRefGoogle Scholar
  26. Huber G, Gorb S, Spolenak R, Arzt E (2005) Resolving the nanoscale adhesion of individual gecko spatulae by atomic force microscopy. Biol Lett 1:2–4CrossRefPubMedGoogle Scholar
  27. Irschick DJ, Austin CC, Petren K, Fisher R, Losos JB, Ellers O (1996) A comparative analysis of clinging ability among pad-bearing lizards. Biol J Linn Soc 59:21–35CrossRefGoogle Scholar
  28. Israelachvili J (1992) Intermolecular and surface forces. Academic, New YorkGoogle Scholar
  29. Johnson KL (1985) Contact mechanics. Cambridge University Press, CambridgeGoogle Scholar
  30. Johnson RE, Dettre RH (1963) Contact angle hysteresis I. Study of an idealized rough surface, chapter 7. In: Fowkes FM (ed) Advances in chemistry series, vol 43, American Chemical Society, Washington DC, pp. 112–129Google Scholar
  31. Johnson KL, Kendall K, Roberts AD (1973) Surface energy and the contact of elastic solids. Proc R Soc Lond A 324:310–313Google Scholar
  32. Kinloch AJ (1987) Adhesion and adhesives: science and technology. Chapman & Hall, New YorkGoogle Scholar
  33. Maderson PFA (1964) Keratinized epidermal derivatives as an aid to climbing in gekkonid lizards. Nature 203:780–781CrossRefGoogle Scholar
  34. Neinhuis C (1997) Characterization and distribution of water-repellent, self-cleaning plant surfaces. Ann Bot 79:667–677CrossRefGoogle Scholar
  35. Patankar NA (2003) On the modeling of hydrophobic contact angles on rough surfaces. Langmuir 19:1249–1253CrossRefGoogle Scholar
  36. Patankar NA (2004) Mimicking the lotus effect: influence of double roughness structures and slender pillars. Langmuir 20:8209–8213PubMedCrossRefGoogle Scholar
  37. Persson BNJ (2003) On the mechanism of adhesion in biological systems. J Chem Phys 118:7614–7621CrossRefGoogle Scholar
  38. Persson BNJ, Gorb S (2003) The effect of surface roughness on the adhesion of elastic plates with application to biological systems. J Chem Phys 119:11437CrossRefGoogle Scholar
  39. Persson BNJ, Albohr O, Tartaglino U, Volokitin AI, Tosatti E (2005) On the nature of surface roughness with application to contact mechanics, sealing, rubber friction and adhesion. J Phys Condens Matter 17:R1–R62CrossRefGoogle Scholar
  40. Pocius AV (2002) Adhesion and adhesives technology: an introduction, 2nd edn. Hanser Verlag, MunichGoogle Scholar
  41. Ruibal R, Ernst V (1965) The structure of the digital setae of lizards. J Morphol 117:271–294PubMedCrossRefGoogle Scholar
  42. Russell AP (1975) A contribution to the functional morphology of the foot of the tokay, Gekko gecko (reptilia, gekkonidae). J Zool (Lond) 176:437–476CrossRefGoogle Scholar
  43. Russell AP (1979) Parallelism and integrated design in the foot structure of gekkonine and diplodactyline geckos. Copeia 1979:1–21CrossRefGoogle Scholar
  44. Russell AP (1986) The morphological basis of weight-bearing in the scansors of the tokay gecko (reptilia: Sauria). Can J Zool 64:948–955CrossRefGoogle Scholar
  45. Schleich HH, Kästle W (1986) Ultrastrukturen an Gecko-Zehen (reptilia: Sauria: Gekkonidae). Amphib-Reptil 7:141–166Google Scholar
  46. Sitti M, Fearing RS (2003) Synthetic gecko foot-hair micro/nano structures as dry adhesives. J Adhes Sci Technol 17:1055–1073CrossRefGoogle Scholar
  47. Spolenak R, Gorb S, Gao HJ, Arzt E (2004) Effects of contact shape on the scaling of biological attachments. Proc Royal Soc Lond A 461:305–319CrossRefGoogle Scholar
  48. Spolenak R, Gorb S, Arzt E (2005) Adhesion design maps for bio-inspired attachment systems. Acta Biomater 1:5–13PubMedCrossRefGoogle Scholar
  49. Stewart G, Daniel R (1972) Scales of the lizard gekko gecko: surface structure examined with the scanning electron microscope. Copeia 1972(2):252–257CrossRefGoogle Scholar
  50. Vinson J, Vinson J-M (1969) The saurian fauna of the Mascarene Islands. Bull Maurit Inst 6:203–320Google Scholar
  51. Wainwright SA, Biggs WD, Currey JD, Gosline JM (1982) Mechanical design in organisms. Princeton University Press, PrincetonGoogle Scholar
  52. Williams EE, Peterson JA (1982) Convergent and alternative designs in the digital adhesive pads of scincid lizards. Science 215:1509–1511CrossRefPubMedGoogle Scholar
  53. Wolfram E, Faust R (1978) Liquid drops on a tilted plate, contact angle hysteresis and the young contact angle. In: Padday JF (ed) Wetting, spreading, and adhesion. Academic, London, pp. 213–226Google Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Department of BiologyLewis and Clark College, 0615 SW Palatine Hill RoadPortlandUSA
  2. 2.Biophysics Graduate GroupUniversity of CaliforniaBerkeleyUSA

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