Spoilsport scientists unstick Spider-Man

You won't be climbing walls with those sticky pads, mate

A team of scientists from the University of Cambridge has disagreeably grounded Spider-Man after concluding that were the arachnohuman crimefighter to use gecko-style sticky pads to scale buildings, they'd need to measure 40 per cent of his body surface.*

That's because the bigger the animal, the less surface area versus volume, as Dr David Labonte, of the uni's Department of Zoology, explained: "As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and an elephant is mostly volume with not much surface area.

"This poses a problem for larger climbing animals because, when they are bigger and heavier, they need more sticking power, but they have comparatively less body surface available for sticky footpads. This implies that there is a maximum size for animals climbing with sticky footpads – and that turns out to be about the size of a gecko."

To come to this conclusion, the team "compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal".

Labonte said: "We covered a range of more than seven orders of magnitude in body weight, which is roughly the same weight difference as between a cockroach and Big Ben.

"Although we were looking at vastly different animals – a spider and a gecko are about as different as a human is to an ant – their sticky feet are remarkably similar."

This example of "convergent evolution", where distinct species arrive at the same solution to a problem via different evolutionary routes, show that the sticky pad plan is "very good solution", according to Labonte.

Not for Spider-Man, sadly, although there is of course another way to overcome the maximum size limit: make the pads stickier. Labonte noted that as tree frogs' size has increased, their pads have become more adhesive, rather than growing in proportion to their embiggenment.

Substantially more gripping power may be a long-term solution for allowing humans to climb vertical surfaces. Back in 2014, Stanford University boffins came up with "a gecko-inspired human climbing system that allowed a grad student to scale a glass wall using two hand-sized sticky pads".

However, while the system outperformed a gecko's feet in terms of adhesion "on relatively flat, smooth and clean vertical glass", it couldn't compete on other, rougher surfaces. There are full details on the research here.

The Cambridge team's research abstract is here. Labonte concluded: "Our study emphasises the importance of scaling for animal adhesion, and scaling is also essential for improving the performance of adhesives over much larger areas.

"There is a lot of interesting work still to be done looking into the strategies that animals use to make their footpads stickier - these would likely have very useful applications in the development of large-scale, powerful yet controllable adhesives." ®

Bootnote

*Practically speaking, this 40 per cent would have to be located on hands and feet, meaning Spidey requires "shoes in European size 145 or US size 114".




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