Table of Contents Author Guidelines Submit a Manuscript
Journal of Nanomaterials
Volume 2008, Article ID 194524, 5 pages
http://dx.doi.org/10.1155/2008/194524
Research Article

Preliminary In Vivo Experiments on Adhesion of Geckos

1Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy
2AO Research Institute, Clevadelstrasse 8, Davos-Platz, Switzerland
3Department of Biomedicine, Unit of Dental Sciences and Biomaterials, University of Trieste, Via Stuparich 1, 34129 Trieste, Italy
4Società Italiana Veterinari per Animali Esotici, Via Trecchi 20, 26100 Cremona, Italy
5National Institute of Nuclear Physic, National Laboratories of Frascati, Via E. Fermi 40, 00044 Frascati, Italy

Received 3 October 2007; Accepted 23 April 2008

Academic Editor: Jun Lou

Copyright © 2008 E. Lepore et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We performed preliminary experiments on the adhesion of a Tokay gecko on surfaces with different roughness, with or without particles with significant different granulometry, before/after or during the moult. The results were analyzed using the Weibull statistics.

1. Introduction

The Tokay gecko (Gekko Gecko) ability to climb or hang upside down to relatively smooth surfaces (Figure 1) is well-known since the past [1]. With a weight up to 300 g these animals exhibit a versatile and effective dry adhesion. Many hypotheses were formulated to explain this peculiarity [218]. Electron microscopy showed that the toes of this animal are covered by hierarchically organized microscopic hairs, further characterized by sub-nanohairs. The application of a similar principle to different fields, for the development of superadhesive smart materials, is nowadays of great interest [1921].

194524.fig.001
Figure 1: Gecko natural downwards position on a plexiglass surface.

The aim of this paper is to describe a preliminary series of experiments performed in vivo on a Tokay gecko. We recorded the gecko adhesive times on two surfaces characterized by significantly different roughness with or without particles with significant different granulometry, before/after or during the moult. We analyzed the adhesive times using classical Weibull statistics.

2. Material and Method

The adhesion capability of a 50 g female Tokay gecko of approximately 20 cm in length was tested gently segregating the animal in a ( cm3) box provided with several air inlets. One wall of the box was made of glass and the rest were made of plexiglass. Experiments were performed at room temperature (°C). All the tests were performed under the supervision of a certified veterinarian. The animal did not show any particular discomfort being manipulated or segregated in the box, except its well-known aggressiveness.

2.1. Characterization of the Surface

The roughness of the materials used to build each face of the box was accurately characterized using a three-dimensional (3D) optical profilometer, Talysurf CLI 1000 (Taylor Hobson) with the CLA Confocal Gauge 300 HE (300 μm range and 10 nm vertical resolution). A surface area of 0.1 mm × 0.1 mm of each material was evaluated at 50 μm/s and 100 Hz sampling rate. The final resolution was 201 points/profile and all parameters of interest were referred to a 25 μm cutoff. The measured roughness parameters were the standard amplitude parameters Sa, Sq, Sp, Sv, Ssk, Sz, and the hybrid parameters Ssk and Sdr. Sa represents the surface arithmetical average roughness; Sq is the mean square roughness and represents the mean square deviation of profile from the middle line; Sp and Sv are, respectively, the height of the highest peak and the deepness of the deepest valley (absolute value); Sz is the average distance between the five highest peaks and the five deepest valleys detected in the analyzed area; the parameter Ssk describes the surface skewness; Sdr is equal to the ratio between effective and nominal surface areas minus one.

2.2. Characterization of the Toe

Four frozen and formaldehyde fixed samples of foots retrieved from two geckos died naturally were unfrozen at room temperature and scanned with a LEICA CLS 150 XE stereoscope and pictures of fields of interest recorded. A LEICA STEREOSCAN 430i electron microscope was used to measure the size of the setae.

The sequence of movements performed by the gecko during adhesion was recorded by gr-dx77u JVC digital video camera. The video camera was located axial to the gecko forearm and perpendicular to the ceiling surface of the box, approximately 25 cm far from the animal body. Single frames were then extracted using Nero Vision software.

2.3. Characterization of the Particles

The adhesion test consisted in the progressive rotation of the box up to 180° with respect to its original position and in the description of the effect of the granulometries of different particles on the gecko adhesion ability. Calcium carbonate particles (50 g) and 2.5 mm diameter plastic spheres (100 g) were used to test two significant different granulometries. In order to test the long-term effect of small granulometry particles, the test using calcium carbonate was repeated also deeply cleaning the box but leaving dirt the animal feet. Plastic spheres were tested both lying freely on the bottom of the box or fixed, in order to form a restrained layer.

2.4. Adhesion Experiments and Weibull Statistics

A standard timer was used to measure the gecko failure times, defined as the number of seconds the animal was able to keep the upside down position before moving into another position (e.g., falling down). Tests were performed during the moult period and during the non-moult period.

The Weibull statistics, widely used for describing the strength and fatigue life in solids, was used to analyze the gecko adhesion ability. Thus, the loss of adhesion was treated as an interfacial failure.

3. Results

3.1. Characterization of the Surface

Surface profiles of glass (Figure 2) and plexiglass (Figure 3) showed two homogeneous surfaces without significant 3D alterations, apart from small isolate bubbles on the glass surface derived from the fabrication process (melting). Table 1 summarizes averaged roughness parameters for the materials of interest. The surface of glass had a larger number of plateaus and several deep thin valleys in comparison to plexiglass.

tab1
Table 1: Superficial roughness parameters of plexiglass and glass.
194524.fig.002
Figure 2: Glass: surface of glass without any superficial treatment.
194524.fig.003
Figure 3: Plexiglass: surface of plexiglass without any superficial treatment.
3.2. Characterization of the Toe

Multiscale observations confirmed classical observations [2231]: the foot of Tokay gecko is characterized by a hierarchical structure starting with macroscopic lamellae, composed by setae, each of them containing different spatulae, representing the terminal contact units (Figure 4). The typical hyperextension of the toes has been clearly observed.

fig5
Figure 4: Scanning electron microscopy of the hierarchical structures of a gecko foot. Each toe contains hundreds of thousands of setae and each seta contains hundreds of spatulae.
3.3. Characterization of the Particles

Small Granulometry
Immediately after feet soiling with calcium carbonate (Figure 5) the ability of gecko to adhere to the surfaces vanished. Repeating the test one hour later no improvement in the adhesive ability of gecko has been observed. Self-cleaning was not observed. The gecko did not try to clean licking or moving quickly its feet and it seemed to be less aggressive, because of its perceived difficulty.

194524.fig.013
Figure 5: A gecko’s dirty foot after treatment: the macroscopic aspect of lamellae is as a compact covered lamella, where the calcium carbonate fills all the empty free spaces between the setae.

Large Granulometry
The unconstrained spheres shifted away under the feet, thus capable of adhering to the underlying surfaces (plexiglass or glass). On the constrained layer made by the same spheres gecko exhibits its typical adhesive properties up to 180 deg rotation (Figure 6), making use also of its claws (Figure 7).

194524.fig.014
Figure 6: Adhesion on a layer of fixed spheres (2.5 mm in diameter).
194524.fig.015
Figure 7: The nails on the tip of each toe.
3.4. Adhesion Experiments and Weibull Statistics

The measured times to failure were treated with Weibull Statistics. Accordingly, the distribution of failure (F) is given by: where t is the measured adhesion time, m is the shape parameter, and is the scale parameter of the distribution of failure (F). The cumulative probability can be obtained experimentally as where N is the total number of performed tests and the measured times of failure, are ranked in an ascending order. The Weibull statistics was found to be appropriate for describing the adhesion times on different surfaces. For example, the first series on plexiglass during the non moult period (measurements are reported in Table 2, Test 1) showed a Weibull modulus with a correlation coefficient of , see Figure 8. The scale parameter was 413.86 seconds, approximately corresponding to 6 minutes and 53 seconds. The time measurements during the moult period (Table 2, Test 2), showed a decrease in the adhesion ability. The scale parameter was 200.79 seconds, approximately corresponding to 3 minutes and 20 seconds. The Weibull modulus during the moult increased up to , with a correlation , see Figure 9.

tab2
Table 2: Measurement results of gecko’s time adhesion on plexiglass surface: first set before the moult; second set during the moult.
194524.fig.016
Figure 8: First set of measurements: Weibull statistics of gecko’s time adhesion before the moult (Table 2, Test 1).
194524.fig.017
Figure 9: Second set of measurements: Weibull statistics of gecko’s time adhesion during the moult (Table 2, Test 2).

We have also observed an extraordinary increase in adhesion’s time during the phase just following the moult, corresponding to adhesion times of the order of 2-3 hours, both on plexiglass and on glass.

The adhesive ability of gecko drastically decreases when the gecko moults. In the first series of measurements of gecko’s time adhesion, the values are strongly variable by spanning between two orders of magnitude, in the range 37−1268 seconds, while the values of the second series obtained from the same gecko but during its moult are much less dispersed, from 59 to 380 seconds. The more variable the failure time, the lower the parameter m. Note that the shape parameter m of the first series (m = 1.36) is lower than in the second case (m = 2.23). As the failure shape parameter suggests, the failure during the moult becomes an almost deterministic process.

4. Conclusions

We have showed that the gecko adhesive ability is drastically reduced when particles characterized by a “small” granulometry are interposed between toe and surface. Large particles can be controlled during adhesion, similarly to the surface roughness. The Weibull Statistics is found to be appropriate to describe the adhesion times of geckos. As the parameter m decreases, the failure time becomes more variable, describing a more stochastic and less deterministic process. This suggests that adhesion becomes a more deterministic process during the moult.

Acknowledgments

The authors would like to thank M. Biasotto of the Department of Special Surgery at the University of Trieste for experimental instruments of surface measurements and S. Toscano, DVM and SIVAE member, for the support for experimental studies. N. Pugno and A. Carpinteri is supported by the “Bando Ricerca Scientifica Piemonte 2006”—BIADS: Novel biomaterials for intraoperative adjustable devices for fine tuning of prostheses shape and performance in surgery.

References

  1. Aristotle, Historia Animalium, Book IX, Part 9, The Clarendon Press, Oxford, UK, 1918.
  2. E. Arzt, S. Gorb, and R. Spolenak, “From micro to nano contacts in biological attachment devices,” Proceedings of the National Academy of Sciences of the United States of America, vol. 100, no. 19, pp. 10603–10606, 2003. View at Publisher · View at Google Scholar · View at PubMed
  3. K. Autumn and A. M. Peattie, “Mechanisms of adhesion in geckos,” Integrative and Comparative Biology, vol. 42, no. 6, pp. 1081–1090, 2002. View at Publisher · View at Google Scholar
  4. D. J. Irschick, C. C. Austin, K. Petren, R. N. Fisher, J. B. Losos, and O. Ellers, “A comparative analysis of clinging ability among pad-bearing lizards,” Biological Journal of the Linnean Society, vol. 59, no. 1, pp. 21–35, 1996. View at Publisher · View at Google Scholar
  5. R. Ruibal and V. Ernst, “The structure of the digital setae of lizards,” Journal of Morphology, vol. 117, no. 3, pp. 271–293, 1965. View at Publisher · View at Google Scholar · View at PubMed
  6. A. P. Russell, “The morphological basis of weight-bearing in the scansors of the tokay gecko (Reptilia: Sauria),” Canadian Journal of Zoology, vol. 64, no. 4, pp. 948–955, 1986. View at Publisher · View at Google Scholar
  7. H. H. Schleich and W. Kästle, “Ultrastrukturen an Gecko-Zehen (Reptilia: Sauria: Gekkonidae),” Amphibia-Reptilia, vol. 7, no. 2, pp. 141–166, 1986. View at Publisher · View at Google Scholar
  8. J. Wagler, Natürliches System der Amphibien, J. G. Cotta'schen Buchhandlung, Munich, Germany, 1830.
  9. K. Autumn, Y. A. Liang, S. T. Hsieh et al., “Adhesive force of a single gecko foot-hair,” Nature, vol. 405, no. 6787, pp. 681–685, 2000. View at Publisher · View at Google Scholar · View at PubMed
  10. P. J. Bergmann and D. J. Irschick, “Effects of temperature on maximum clinging ability in a diurnal gecko: evidence for a passive clinging mechanism?” Journal of Experimental Zoology A, vol. 303, no. 9, pp. 785–791, 2005. View at Publisher · View at Google Scholar · View at PubMed
  11. W.-D. Dellit, “Zur Anatomie und Physiologie der Geckozehe,” Jenaische Zeitschrift für Naturwissenschaft, vol. 68, pp. 613–658, 1934. View at Google Scholar
  12. J. G. J. Gennaro, “The gecko grip,” Journal of Natural History, vol. 78, pp. 36–43, 1969. View at Google Scholar
  13. U. Hiller, “Untersuchungen zum Feinbau und zur Funktion der Haftborsten von Reptilien,” Zeitschrift für Morphologie der Tiere, vol. 62, no. 4, pp. 307–362, 1968. View at Publisher · View at Google Scholar
  14. G. Huber, H. Mantz, R. Spolenak et al., “Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 45, pp. 16293–16296, 2005. View at Publisher · View at Google Scholar · View at PubMed
  15. H. R. Schmidt, “Zur Anatomie und Physiologie der Geckopfote,” Jenaische Zeitschrift für Naturwissenschaft, vol. 39, pp. 551–563, 1904. View at Google Scholar
  16. G. Simmermacher, “Untersuchungen über Haftapparate an Tarsalgliedern von Insekten,” Zeitschrift für Wissenschaftliche Zoologie, vol. 40, pp. 481–556, 1884. View at Google Scholar
  17. N. E. Stork, “Experimental analysis of adhesion of Chrysolina polita (Chrysomelidae: Coleoptera) on a variety of surfaces,” Journal of Experimental Biology, vol. 88, no. 1, pp. 91–107, 1980. View at Google Scholar
  18. G. Huber, S. N. Gorb, R. Spolenak, and E. Arzt, “Resolving the nanoscale adhesion of individual gecko spatulae by atomic force microscopy,” Biology Letters, vol. 1, no. 1, pp. 2–4, 2005. View at Publisher · View at Google Scholar · View at PubMed
  19. M. T. Northen and K. L. Turner, “A batch fabricated biomimetic dry adhesive,” Nanotechnology, vol. 16, no. 8, pp. 1159–1166, 2005. View at Publisher · View at Google Scholar
  20. B. Yurdumakan, N. R. Raravikar, P. M. Ajayan, and A. Dhinojwala, “Synthetic gecko foot-hairs from multiwalled carbon nanotubes,” Chemical Communications, no. 30, pp. 3799–3801, 2005. View at Publisher · View at Google Scholar · View at PubMed
  21. H. Lee, B. P. Lee, and P. B. Messersmith, “A reversible wet/dry adhesive inspired by mussels and geckos,” Nature, vol. 448, no. 7151, pp. 338–341, 2007. View at Publisher · View at Google Scholar · View at PubMed
  22. A. P. Russell, “A contribution to the functional morphology of the foot of the tokay, Gekko gecko (Reptilia, Gekkonidae),” Journal of Zoology, vol. 176, pp. 437–476, 1975. View at Google Scholar
  23. E. E. Williams and J. A. Peterson, “Convergent and alternative designs in the digital adhesive pads of scincid lizards,” Science, vol. 215, no. 4539, pp. 1509–1511, 1982. View at Publisher · View at Google Scholar · View at PubMed
  24. B. N. J. Persson and S. Gorb, “The effect of surface roughness on the adhesion of elastic plates with application to biological systems,” Journal of Chemical Physics, vol. 119, no. 21, pp. 11437–11444, 2003. View at Publisher · View at Google Scholar
  25. N. M. Pugno, “Towards a Spiderman suit: large invisible cables and self-cleaning releasable superadhesive materials,” Journal of Physics Condensed Matter, vol. 19, no. 39, Article ID 395001, 17 pages, 2007. View at Publisher · View at Google Scholar
  26. K. Autumn, “How gecko toes stick,” American Scientist, vol. 94, no. 3, pp. 124–132, 2006. View at Publisher · View at Google Scholar
  27. H. Gao, X. Wang, H. Yao, S. Gorb, and E. Arzt, “Mechanics of hierarchical adhesion structures of geckos,” Mechanics of Materials, vol. 37, no. 2-3, pp. 275–285, 2005. View at Publisher · View at Google Scholar
  28. K. Autumn, A. Dittmore, D. Santos, M. Spenko, and M. Cutkosky, “Frictional adhesion: a new angle on gecko attachment,” Journal of Experimental Biology, vol. 209, no. 18, pp. 3569–3579, 2006. View at Publisher · View at Google Scholar · View at PubMed
  29. W. R. Hansen and K. Autumn, “Evidence for self-cleaning in gecko setae,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 2, pp. 385–389, 2005. View at Publisher · View at Google Scholar · View at PubMed
  30. G. Huber, S. N. Gorb, N. Hosoda, R. Spolenak, and E. Arzt, “Influence of surface roughness on gecko adhesion,” Acta Biomaterialia, vol. 3, no. 4, pp. 607–610, 2007. View at Publisher · View at Google Scholar · View at PubMed
  31. K. Autumn, M. Sitti, Y. A. Liang et al., “Evidence for van der Waals adhesion in gecko setae,” Proceedings of the National Academy of Sciences of the United States of America, vol. 99, no. 19, pp. 12252–12256, 2002. View at Publisher · View at Google Scholar · View at PubMed