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We might suppose our technology is first class. With computers, satellites and precision devices, our society happily adapts to ever more sophisticated machines. Each achievement provides the platform for new uses of technology and further inventions. Rather than giving thanks for these insights, all too often we pride ourselves for our knowledge.

The fact is however that our devices and skills are clumsy compared to the exquisite gifts conferred on living creatures. Like the lilies that do not spin fine fabric, yet are more beautifully clothed than man in his fanciest garb, so even small creatures have technological skills that put our best efforts to shame.

Some scientists talk about irreducible complexity or intelligent design. These organisms demonstrate all of that. However, just like the wise man who considered the habits of ants, we feel enriched and filled with awe when we consider the results of modern studies into the wonders of the creation.

Upside down

Apparently it was Aristotle, the ancient Greek philosopher and naturalist, who first wondered about the abilities of geckos to scamper up vertical walls and across smooth ceilings. People have wondered ever since about these dramatic talents, but only recently have scientists discovered some answers.

Geckos are small nocturnal lizards which live in all the warm regions of the world including the Mediterranean area. The species of choice for research is the Tokay gecko (Gecko gecko) which can grow as long as 35 cm (14 inches), and which weighs up to 100 g. That is a hefty creature to hang upside down from a smooth surface. The American military and other parties interested in commercial exploitation of such an astonishing adhesive, have heavily invested in this research.

Firstly interested scientists sought to eliminate all likely processes which the gecko does not employ. To do this they began by examining the soles of gecko feet. If the gecko used any kind of glue there would have to be glands to secrete the material. However there are no glands and the gecko leaves no residue on a surface after it has passed by.

What is on the pads of their feet are about one half million very thin short hairs arranged in distinctive patterns. Ends of these hairs, called setae, are in their turn divided into about 1000 submicroscopic filaments called spatulae. Generally in biology the term spatulate means an almost spoon shaped, but flat, end.

It was long popularly assumed that the spatulate endings function like suction cups. Nevertheless the fact that their feet work even in a vacuum effectively disproved that idea. Moreover their feet stick to surfaces even when the air is electrically charged. Thus it must not be electrostatic attraction (such as when hair sticks to a balloon rubbed on a rough surface) which allows the geckos to work their “magic”.

Evidently obvious explanations do not work, so something a lot more subtle and sophisticated must be involved. Within the past three years, a team of American scientists has discovered that an obscure phenomenon which accounts for the fact that water stays together as a liquid rather than dispersing as a gas, is the principle operating here.

It was Johannes Diderik van der Waals (1837-1923) who discovered that even molecules with no potential for chemical bonding between themselves, are in fact weakly attracted to each other if the molecules are pushed closely enough together. What apparently happens is that individual molecules in the gecko spatulae and in the surface material trade electrical charges. A weak electrical bond is formed, which when multiplied by the number of spatulae per foot, acts like a powerful electrical glue. The molecules of the foot and surface material in effect are drawn together into a composite structure.

Such a van der Waals force is all very well as an explanation for sticking the gecko to a surface, but these animals do not remain permanently anchored in one location. In order to walk or run, they must become unstuck again. Apparently the animal simply moves the foot so that the setae are peeled away from the surface. To engage the setae, the animal pushes the foot backwards and to remove, he pulls it forward.

Dutch physicist van der Waals received a Nobel Prize in 1910 for his discovery of this force. It remains to be seen what reward will accrue to the modern researchers who hope to exploit such knowledge to produce a powerful adhesive.

Those involved in these pursuits admit that we do not at present have the expertise or know-how to engineer structures as exquisite as the gecko foot. An English team from University of Manchester recently produced a postage stamp sized piece of “synthetic gecko-tape.” This ‘invention’ is covered in millions of plastic polymer ‘hairs’ and it works! The product is so effective that it could suspend a person by one hand from a ceiling.

Nevertheless, although applications of the concept are “nearly limitless”, the actual product exhibits some distinct disadvantages.

While the real product continues to work throughout a gecko lifetime, the synthetic tape stayed sticky for only seven or eight applications. Moreover the artificial version is unbelievably expensive. A one metre square piece of tape would cost tens of thousands of English pounds to produce. Thus not surprisingly, frenetic research continues on this project. Even the Canadian government has leaped into the fray with a $200,000 grant over five years to a zoologist at University of Calgary. In this era of reduced government expenditures, that is a lot of money for one research project. The Canadian government must be expecting a good financial return on their investment! Meanwhile all involved agree that the living creatures themselves are the place to look for further ideas and inspiration.


Moxie
April 2004

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