Drops explode off gecko skin
Gecko skin microstructure also kills bacteria
Geckos are well known for their ability to stick to almost anything—they can even walk upside down on polished glass. Only in this millennium has the secret of the gecko’s stickiness been uncovered: its feet are covered with extremely fine hairs that exploit ultra-short range attractive forces between atoms.1,2 They avoid getting stuck because the hairs are curved, and store energy like a spring.3,4 Gecko feet are also self-cleaning,5 and have inspired a totally new type of self-cleaning adhesive tape.6,7 This design has been used to make an adhesive of carbon nanotubes that can be applied to circuit boards without the high heat needed for soldering.8
Now scientists from universities in Queensland, Australia, including the husband-and-wife team of Drs Gregory and Jolanta Watson, have analyzed the box-patterned gecko, Lucasium steindachneri. They discovered equally remarkable fine structure on gecko skin. But instead of attracting, it repels. The skin is covered with tiny dome-shaped scales about 250 microns (µm) in diameter in a hexagonal pattern (1 µm = 10–6 m). In turn, these scales comprise microscopic spinules (‘hairs’) only a few hundred to a few thousand nanometres (nm, 10–9 m) long, with less than a micron separating them. These hairs have an extremely fine tip, with a radius of curvature of only 10–20 nm. In between the scales, the skin is also covered with spinules.9
The nano-scale tips mean that dirt particles have only a tiny surface to stick to, so the skin stays clean. The hairs also repel any water, making the skin hydrophobic (from Greek meaning ‘water-fearing’). The tiny domes are also important, because tiny water droplets will roll into the valleys between the domes. Gravity and wind makes these droplets roll more, and they clean off dirt in the process.10
These droplets coalesce together with startling effects. Droplets are held together with surface tension, or high energy per unit area. When two small droplets combine into a large one, the surface is sharply reduced, which means the total surface energy also drops sharply. But ever since God finished creating after Day 6 (Genesis 2:1), energy can neither be created nor destroyed (the First Law of Thermodynamics). So it must go somewhere—and it goes into propelling the droplets off the surface, dubbed ‘geckovescence’.11 Thus the gecko skin is so water-repellent that it is called ‘super-hydrophobic’. The skin also repels other liquids such as coffee, soy sauce, vinegar, red wine, milk, cola, and blood.12
Because geckos are so small, they have a high skin surface area compared to their mass. This would be an open invitation to disease germs. But the skin structure quickly kills soft-walled ‘Gram-negative’ bacteria, often the most dangerous. Some insight into the mechanism might come from the germ-killing cicada wing that has nano-pillars far smaller than germs. Work by a team including the Watsons shows that the germ is attracted to the surface, but the cell wall stretches into the gaps between the pillars until it bursts.13,14 However, human cells are safe on the skin.
Copying the design
Scientists are now trying to make materials that copy the gecko skin structure. There would be many uses for a self-cleaning water-repelling fabric, and its anti-bacterial properties would be especially useful for hospitals. The gecko skin is not only anti-bacterial, but is safe on human skin. And because it’s safe on human cells, it could be used for bio-compatible implants that would resist ‘superbug’ infection,15 as well as a surface to grow human stem cells.16,17
Created or evolved?
Copying the designs of living creatures is called biomimetics or biomimicry, and is a rapidly expanding field.18 Dr Gregory Watson pointed out how useful this is:
“Nature has already figured out the best ways of dealing with certain problems. It’s just a matter of us catching up to that and figuring out how we can make it work for us. My philosophy has always been why reinvent the wheel when you can figure out how it works.”
Of course, ‘nature’ can’t figure out anything. Only an intelligence can do that. And since it takes high intelligence to make the copies, how much more would it take to invent the originals?
Another article reports:
“Jolanta Watson reckons that this phenomenon might have evolved to prevent moisture-loving microbes from thriving on the lizard’s skin, and it might also work as a self-cleaning mechanism.”19
As we often see in biomimetics papers, there is a fact-free homage to evolution. In reality, it was a statement only about current function, which is better explained by design for this function. There was not the slightest proposal for how this system evolved by random mutations and natural selection at each step, let alone evidence. We have often pointed out that explaining function or advantage of a feature is not at all the same as explaining how this came to be.20
References and notes
- Autumn, K. et al., Adhesive force of a single gecko foot hair, Nature 405(6787):681–685, 2000 | doi:10.1038/3501507; perspective by Gee, H., Gripping feat, same issue, p. 631. Return to text.
- After Sarfati, J., Great gecko glue? Creation 23(1):54–55, 2000; creation.com/gecko. Return to text.
- Hu, C. and Greaney, P.A., Role of seta angle and flexibility in the gecko adhesion mechanism, Journal of Applied Physics 116:074302 | doi:10.1063/1.4892628, 12 August 2014. Return to text.
- Sarfati, J., How geckos become unstuck, Creation 37(2):25, 2015. Return to text.
- Hansen, W.R. and Autumn, K., Evidence for self-cleaning in gecko setae, PNAS 102(2):385–389, 11 January 2005 | doi:10.1073/pnas.0408304102. Return to text.
- Geim, A.K. et al., Microfabricated adhesive mimicking gecko foot-hair, Nature Materials 2:461–463, 2003 | doi:10.1038/nmat917. Return to text.
- After Sarfati, J., Gecko foot design—could it lead to a real ‘spiderman’? Creation 26(1):22–23, 2003; creation.com/geckoman. Return to text.
- Johnson, C.J., Conductive adhesive could replace solder, EE|Times (Connecting the global electronics community), 14 October 2008. Return to text.
- Watson, G.S. et al., A gecko skin micro/nano structure—A low adhesion, superhydrophobic, anti-wetting, self-cleaning, biocompatible, antibacterial surface, Acta Biomaterialia 21:109–122, 15 July 2015 | doi:10.1016/j.actbio.2015.03.007. Return to text.
- Watson, G.S. et al., Removal mechanisms of dew via self-propulsion off the gecko skin, Interface, 11 March 2015 | doi:10.1098/rsif.2014.1396. Return to text.
- Urquhart, J., Watch this gecko’s explosive self-cleaning trick, newscientist.com, 11 March 2015. This article includes a video of the droplets exploding off the skin, and shows the skin nano-structure. Return to text.
- Loomis, I., Why you’ll never see a dirty gecko: Geckos have self-cleaning skin that helps the lizards stay dry and healthy, Student Science, student.societyforscience.org, 30 March 2015. Return to text.
- Pogodin, S. et al., Biophysical model of bacterial cell interactions with nanopatterned cicada wing surfaces, Biophysical Journal 104(4):835–840, 19 February 2013 | doi:10.1016/j.bpj.2012.12.046. Return to text.
- Cicada wings pop bacteria, Creation 35(3):8, 2013. Return to text.
- However, see Wieland, C., Superbugs not super after all, Creation 20(1):10–13, 1997; creation.com/superbug. Return to text.
- Watson, J., New research has found replicating the skin of a gecko could have remarkable industrial, scientific and medical applications, ABC News Radio (audio), abc.net.au, 11 June 2015. Return to text.
- Adult stem cells are both effective and ethical, while embryonic stem cells are neither. Sarfati, J., Stem cells and Genesis, J. Creation 15(3):19–26, 2001; creation.com/stem-cells. Return to text.
- See articles under creation.com/design#biomimetics. Return to text.
- Urquhart, Ref. 11. Return to text.
- Doyle, S., Does biological advantage imply biological origin? J. Creation 26(1):10–12, 2012; creation.com/biological-advantage. Return to text.