An Engineer In Wonderland – Copying Geckos

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I am fascinated by the potential of biomimetics.

Years ago I fell into conversation with an academic biologist.

He told me that if you want to make stuff, find an enzyme to do it because enzymes, which are nature’s catalysts, do things very well – generally far more effectively than simple chemicals or thermal processes.
They work by pushing just the right electro-chemical buttons to make reactions happen – putting a key in the lock rather than breaking the door down.

Enzymes cannot be designed from the ground up for specific tasks at the moment because most of them are proteins and ‘the protein folding problem’ – what shape any given protein will end up, and where its charges will be – has yet to be solved.

This is not because no one knows how to do it, but because there isn’t enough free computer time in the world to have much of a stab at it.

IBM’s original Blue Gene supercomputer was specifically designed to model protein folding.

Destined to be the most powerful computer ever made, it seems to be one of the great IBM ‘hey, this would be interesting and might do a lot of good’ projects.

I don’t think it was ever finished in its intended form, instead it morphed into the smaller Blue Gene/L and IBM span off a commercial line of Blue Gene computers.

Anyway, until enzymes can be designed, researchers continue to trawl nature for ones that can turn cellulose into petrol for ‘good’ biofuels, make hydrogen from sunlight, and lots of other potentially useful things.

This brings me to a slightly simpler bio mystery that has just been emulated – by another nano technology.

Amazingly, Geckos can run across and remain motionless on smooth vertical glass.
More amazingly, despite being super-sticky, they can lift their feet off the glass when they want.

After much speculation and research, it turns out that no glue or micro suckers are involved, just nanometre structures on their toes that exploit van der Waals forces.

There are tiny, but as there are an awful lot of the structures on each Gecko toe, the forces add up to something useful.

The effect has been mimicked to some extent before but a US team – the University of Dayton and Akron, with Georgia Tech and the US Air Force – has done it well.
Tests have been done on surfaces including glass, polymer sheet, Teflon and rough sandpaper, with forces up to 100N/cm2 measured in shear, dropping to 10N/cm2 along the normal – allowing support and removal respectively.

According to the team, the key is making a mat of multi-walled carbon nanotubes standing up like bamboo, with what the team calls “curly entangled tops” that mimic the hierarchical structure of real gecko feet – including branching hairs of different diameters.

When pressed onto a vertical surface, the tangled portion of the nanotubes becomes aligned in contact with the surface and dramatically increases the amount of contact between the nanotubes and the surface, maximising the van der Waals forces that occur at the atomic scale.

When lifted off the surface along the normal, only the tips remain in contact, minimising attraction.

Resistance to shear, apparently, increases with the length of the nanotubes, while the resistance to normal force is independent of length.

The scientist are looking at replacing solder with their material, and proposing it as a dry-out-proof glue for space.



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(Picture – Baby Gecko by jpockele, under Creative Commons Attribution Licence)

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