Ewen Keller, TWI Ltd
This week we're asking what's the most amazing animal? Talking to Ginny Smith, Ewen Keller with us now who works for TWI Limited, studying what makes things sticky...
Ewen - Geckos are natureís best exponents of stickiness. An awful lot insects especially show how you can stick to things, flies, walking around on ceilings and up glass panels, and also, various plants also use stickiness to catch their prey like sundew in the bogs. But geckos do it in a completely different way. Their stickiness is what's called dry adhesion. So, they leave no mark after theyíve gone. So, they're not using any sticky compound like the glue you would have used in the classroom. Now, geckos are also pretty cool because they're really cute and they run around. They donít have any eyelids so they tend to just lick their eyes when they need them cleaned which is quite fun to look at. But what really sets them apart is the fact that they can literally walk up walls. They are natureís Spidermen if weíre going to use the superman analogy thatís already been used. Probably a lot better than Spiderman actually. Geckos have been around for a very long time, over 100 million years. We actually know that they could walk up things 100 million years ago because theyíve actually found some fossilised in amber and they can actually see they're on their feet. They still have the same structures, the same type of skin that allows them to do this. Basically, until about 2002, nobody really fully understood how this happened. So, what weíre now talking about are geckos harnessing the laws of physics. So, they actually got a really good scientific head on to actually capture and use the forces of nature at the smallest level, what we call the nanolevel. If you take a millimetre divide it by a thousand, you get a micron. You divide that by a thousand again, you get a nanometre. So, weíre working at a very, very, very fine level. What they found when they looked at the gecko feet under the microscope Ė it was the electron microscope Ė they found that on their feet were tiny hairs. These hairs which are called setae, whilst these are little hair-like structures on the ends of these little hair-like structures, there were even smaller hairs. These smaller hairs are called spatulae and basically, if we try and get some idea of scale, if you take a setae, you can get 14,000 of them on one square millimetre. On top of each of these setae, you can get about 500 spatulae on top of that. So, you can imagine, itís basically a column with tiny little hairs on which you get even finer hairs on. These tiny little hairs use a force called van der Waals forces which are all around us. And in fact, we use them and we experience them in terms of friction amongst other things when you want to hang on to something. But what this allows a gecko to do is, it allows these tiny hairs to get very close to the surface of glass or the ceiling or a tree or a leaf. And the natural forces, these natural harnessing of physics actually enables them to stick. Now, they donít actually need to stick very significantly because most geckos are quite light. They're about 20 grams actually, a lot of them. But if you could harness every single one of these spatulae, one gecko, with all his fingers and all his toes could actually take a weight of 133 kilograms thatís two human beings.
Ginny - So, could you hang off a gecko?
Ewen - If the gecko was properly attached, yes. But I donít think they'd thank you for it!
Ginny - Now, youíve been talking about how the geckos can produce these amazing forces. But weíve got a demo here thatís going to show everyone how powerful friction can be. So, what have we got here?
Ewen - What weíve got here are two books which you imagine, they open ends facing one another where each page is interleaved with the other to actually then give a really large surface area of the paper in contact with the other book to enable the maximum amount of friction to occur.
Ginny - So, the two books that goes page from book one, page from book two, page from book one, page from book two, all the way through. So, they're touching over 200-odd pages. Who thinks they're quite strong? Okay, what's your name?
Gavin - Gavin.
Ginny - And your name?
Davin - Davin.
Ginny - Gavin and Davin, okay fantastic! Now, what weíre going to do is weíre going to have a little tug of war between you two. So, if you stand facing each other and one of you is going to hold on to the spine of this book and the other one is going to hold on to the spine of the other book. When I say go, I want you to pull. Okay, ready, one, two, three, go!
You donít look like youíve made any difference to that book. Were you pulling as hard as you could?
Gavin - Yes.
Davin - I think it might be just glued.
Ginny - You think it might be glued. He doesnít believe me. Okay, now Georgia is having a go. Itís really, really difficult and that is the same idea as the geckoís.
Ewen - In principle, yes. Itís about getting literally the atoms of the surface close together between one surface in the next that allows this special attraction called Van De Waalís forces to actually work. Itís all pervasive with the gecko that all the gecko needs to do is, it just sort of stops and he can hang on for hours.
Ginny - So, heís not using his muscles to hold on to the wall.
Ewen - Not at all. But one question that no oneís asked is how then do they unstick which I suppose I better explain because basically, I called these tiny, tiny hairs spatulae. So, itís like a spatula in cooking, a bit like a wooden spoon with a big flat end. And thatís the structure of these tiny little features is theyíve got this little angled foot. And basically, what it means is when the gecko actually climbs, it cools down a little bit and then it sticks. When it wants to move on, it lifts and peels them off. It can peel it off with virtually no force.
Ginny - So, I just saw Georgia just checking that I hadnít glued it and unpeeling each layer of the book and it does. It just unpeels very, very easily and you can see that itís not glued. Thatís the same thing that the gecko is doing again.
Ewen - Absolutely.
Ginny - Ewen Keller, thank you very much. Time to hear from our judges now. Whoís got a comment or a question for Ewen?
Georgia - Firstly, do the geckos have to be alive for it to work?
Ewen - The phenomena works with the geckos being well and truly dead, as well as being alive though they can't obviously move their feet themselves.
Georgia - I'm wondering. Can I strap some geckos together and make gecko gloves and climb up buildings?
Ewen - Well again, this is virtually a reality now. They're already are starting to show synthetic versions of this where a man has been demonstrated to climbing up a glass wall. It was only a year or so ago. So, the world of Spiderman is going to become a reality.
Max - Itís incredible that geckos can do this, but I've done some work in the tropics. I've definitely seen a gecko fall off the ceiling. So, if they're so strong, how can they fall off?
Ewen - Well I guess, like anything, there's always clumsy geckos out there. If itís a very, very wet surface then the adhesion will drop off. So, it could be that it was just a very, very wet area.
Gavin - Does it share this sticky thing ability with the tree frog?
Ewen - Itís true to say that there are other some other reptiles and maybe some amphibians who have a similar property. Itís predominantly the geckos, but it isnít unique to geckos. There are some other lizards that would do it.
Ginny - If our judges are ready, can we have your scores please.
George - 7
Georgia - Big fan of the geckos, I'm going to go with an 8.
Max - 7.
Ginny - One final round of applause for Ewen Keller.