In researching his book on bio-inspiration, The Gecko’s Foot, Peter Forbes made a discovery of his own – his idea has now born fruit, but not quite in the way he’d hoped:
I am not a scientist or inventor but a writer. For the last seven years I’ve been researching the new science of bio-inspiration – engineering solutions derived from nature’s own mechanisms, The Gecko’s Foot (Fourth Estate). Bio-inspiration, or biomimetics as it is often called, is a new multidisciplinary science – to get results biologists have to talk to chemists, have to talk to physicists, have to talk to engineers, and so on. An armchair researcher such as myself gets a very broad view of many subjects. You might even make a discovery or two. I did.
The gecko’s foot is one of the big stories in bio-inspiration. For centuries, people could only wonder at the gecko’s ability to climb a smooth vertical wall either up or down, to walk across the ceiling, or to rest for half an hour upside down on the wall with no apparent strain.
Then in 2000, researchers at Berkeley, University of California, and Lewis and Clark College, Portland, Oregon, discovered the gecko’s secret. It has about half a million bristles on each foot and each bristle has between 100 and 1000 split ends with spoon-like tips. A gecko’s foot can touch a surface more intimately than any creature on earth. And it is the intimate contact that creates its clinging ability by means of molecular forces known as van der Waals forces. There’s nothing new about these forces – they were discovered by M. van der Waals in1873 – but until 2000 no one could quite believe that on their own they could account for the gecko’s sticky powers.
There was nothing particular to the gecko in this mechanism; life wasn’t necessary: according to Kellar Autumn, the gecko man at Lewis and Clark, a dead gecko will stay stuck to the wall for as long as you like, and its stickiness happens whenever you have enough fine hairs per unit area. So the race was on to make synthetic gecko tape. Gecko gloves would enable you to scale a building spiderman style and Kellar Autumn’s’ seven-year-old daughter was set on becoming the first Gecko Girl. In January 2004 the Berkeley/Oregon team took out a patent on the mechanism, detailing many possible ways of creating synthetic gecko hairs and hence a gecko adhesive strip.
The gecko story was always prime. In 2002 it briefly hit the newspapers when Andre Geim, a physicist at Manchester University, made a small square of synthetic gecko tape and used it to stick a toy Spiderman to the ceiling. It wasn’t nearly as good as the real thing but, as Geim said, it “proved the principle”. And, scaled up, that sample of synthetic gecko tape would have stuck a man to the ceiling.
Researching the book, I came across many techniques that might or might not be relevant to bio-inspired solutions. Bio-inspiration’s closest cousin is nanotechnology, the science of the very small, and the hot subject in nanotechnology is carbon nanotubes. So I read a lot about these amazing little structures without being sure how relevant they were going to be to my book.
Carbon nanotubes are in the front line of nanotechnology for several reasons. To grasp what they are, imagine a roll of chicken wire writ small – very small. The nanotube story starts with the discovery of buckminsterfullerene or the buckyball in 1985. Buckminsterfullerene is a molecule of 60 carbon atoms in the form of a football, with mixed hexagons and pentagons in the classic pattern of Buckminster Fuller’s domes.
The carbon nanotube (discovered in 1991) is the buckyball’s close cousin. Instead of a sphere, this is a long rolled tube – a nano chicken wire. This molecular chicken wire has a hexagonal lattice structure just like the big stuff: you can roll it up and link the ends to create a single-walled nanotube (SWN) or you can roll it over and over to create a multiwalled nanotube (MWN). Both these kinds of carbon nanotubes exist. Carbon nanotubes are very small, at the bottom end of the nano realm (single-walled nanotubes are only 1-2 nanometres across, multiwalled 10-30 nanometres). Computer chip engineers are particularly interested in nanotubes because not only are they far smaller than the etched silicon circuits currently used, carbon nanotubes actually have the requisite properties built in. Nanotubes can be transistors, light-emitting diodes or fulfil a variety of other electronic functions. But so far nanotubes are mostly a brilliant solution waiting for someone to ask the right question.
In 2002, in the journal Nature, I came across a neat trick with nanotubes. Bingqing Wei, a Chinese researcher, then at Rensselaer Polytechnic Institute, Troy, New York State, discovered that you can seed the growth of nanotube pillars on a prepared silicon template. To create the nanotube pillars Wei first creates a pattern – an array of equispaced silicon dioxide circles on silicon – by etching with standard semiconductor lithographic techniques. When a carbon-containing vapour is exposed to the surface at 800 degrees carbon nanotubes begin to grow out of the circles. The advantage of this technique is that very ordered arrays can be created to almost any density and length.
You didn’t have to be a rocket scientist (you had to be a biomimetician) to realise that the pillars formed could do duty as artificial gecko hairs – In Wei’s experiment the pillars were coarse (about 10,000 nanometres in diameter) but individual multiwall nanotubes – only 10-30 nanometres diameter – would be ideal for gecko hairs.
Instead of just reporting the new work, I decided at this point to get involved. In October 2003 I emailed Bingqing Wei to explain my idea. He wrote back the same day to say that it was indeed plausible and that he would set his student onto it. The schedules of book production and scientific research do not mesh easily. By the time the book had to go to bed at the end of 2004 the nanotubes for gecko hairs experiment had still not delivered any results.
There’s nothing like publishing a book for flushing out material that should have been included. Three days after publication, I was Googling the book’s title and in the top five searches there appeared ‘Synthetic gecko foot-hairs from multiwalled carbon nanotubes’. This turned out to be a paper in the British journal Chemical Communications by a team based at the University of Akron, Ohio. One of the team was an old colleague of Professor Wei from the Rensselaer Polytechnic Institute and he had worked on the idea independently. From my armchair I had experienced a classic moment of the scientific life: the disappointment of having a valid idea but then seeing someone else get there first.
I was both pleased my idea had come off at last and miffed that someone else had independently come to the same conclusion. Had I just missed making my fortune? I had got so close up to the work that I was able to make a small discovery. At that point I didn’t know how to handle it. I could, I suppose, have written a short scientific paper and tried to establish my priority that way. Would a scientific journal have accepted a paper from an armchair scientist? I could have attempted to take out a patent but that is an expensive and convoluted process even for an expert. I would have needed technical help to write the patent application. So it seemed best to write to someone who could progress the idea. The results will be published soon.
It’s now open season for gecko solutions because the nanotube gecko adhesive is a nano Velcro for the 21st century. Could it become as ubiquitous? The Akron team reported that the nanotube array is 200 times stronger than natural gecko bristles. Quite how this can be is beyond me – perhaps it will not be confirmed but if true it is revolutionary. Just to have large quantities of dry adhesive as powerful as the gecko would have many applications in technology. But 200 times more powerful?! As to how far this idea will go we are in the dark.
As T. S. Eliot said, “Between the idea / And the reality / Between the motion / And the act / Falls the Shadow”.
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