Now that I've mentioned The Gecko's Foot, this is a good time to talk about why this appendage is an icon for cool science and bioinspiration. Why is the gecko so interesting to material scientists? Because it can do this! That photo hasn't been rotated. The gecko is literally sticking to glass upside down, and the best part is that it's barely expending any energy! This is an often sought-after skill among espionage experts. Science is getting closer to making those gloves a reality as we unravel and replicate the gecko's secrets. One of the most alluring properties of the adhesion of gecko toes is that they stay completely dry. There's no goo on their feet and no residue left behind on the surface. This is good for spies that don't want to leave a trace, it's a more solid grip than suction cups, and works on more surfaces than magnets. So what is the mechanism behind this completely clean stickiness? It has to do with physical forces that only work on the nano-scale. The gecko's foot is a much more complex surface when you put it under a microscope. It has rows of lamellae on its toepads that are made up of small hairs, which split off into even tinier setae that end in flat spatulas. Why so many minuscule bristles? As I said, the adhesive forces operate at the nano-scale, so the foot must make as many contact points as possible at this scale. What we see as flat surfaces with our unaided eyes are in fact rugged terrains of peaks and valleys when you zoom in: This densely packed array of setae offers a lot more flexibility to the surface of the foot than normal skin would. All of those teeny hairs can bend and compress until they precisely match the topography of the whatever they're trying to stick to. Once you get lizard and glass into such close contact, a phenomenon known as van der Waals forces takes over. This is an attractive force that exists between all atoms that get within a few nanometers of each other. It's not an excessively strong force, but when it's maximized over a large scale, the power adds up quickly. Van der Waals adhesion was first noticed in the gecko, but it's an important mechanism in many other animals. Hm, what else climbs on smooth, often vertical surfaces... Spiders have structures called scopulae that are similarly made up of tiny bristles. They generally have fewer setae than geckos, however, since there is an inverse relationship between the weight of the animal and the number of hair-contacts needed to support it. A spider is lighter than a gecko, so it doesn't require as much van der Waals force to sustain its adhesion to a surface. The first Spider-Man movie (pictured above) got close to addressing the source of Peter Parker's stickiness correctly, but they just missed the target. One scene shortly after his genetic transformation zooms in on his thumb and shows small hairs with intricate structures emerging from his skin. It's a nice try, but those hairs are too widely spaced apart to have any meaningful nano-scale interactions with the brick buildings of New York City. The movie seemed as though it were going for more of a barb-like projection, but that idea falls short as well. Those spines are far to tiny to maintain enough strength to support a man's weight over such a small surface area. And besides, Peter just covers up his sticky hands with gloves anyway! Not to mention the shoes he wears that thwart any possibility of additional adhesion with his feet. That's why X-Men nemesis and member of the Brotherhood of Mutants villain Toad is a more logically sticky character. Toad's gloves only cover his palms, leaving his adhesive fingers plenty of freedom to van der Waals where they please. His palms would offer added stability, but hilarious experiments with geckos have shown that they have enough excess stick-to-it-iveness in their pads that just a single toe is sufficient suspend their entire body. Amphibians do have a slightly different adhesive style however, and a more wet one. Wet adhesion means that we're not as interested in adapting tree frog toepads into industrial nanomaterials because they require a constant reapplication of fluids, whereas gecko feet are more clean and can operate without a living gecko. Recent research has shown that tree frogs do appear to employ some close contact attractive forces with surfaces. Those hexagonal epithelial cells on its toes provide the same flexibility as gecko setae, but at a slightly larger scale. The wetness comes from the fluid mucus that flows in the channels between those flat-ended pegs. Going back to industrial applications, where is my gecko tape?? Rest assured, engineers are working on it as we speak. Andre Geim has had success in replicating the functional nanostructures of gecko feet and making workable gecko tape. The process still needs to be refined, however, before it can be made on a bigger scale and as durable as the gecko feet themselves. The dream of nearly infinitely reusable and mess-free tape is nearly upon us! In reality, most household tapes are good enough already that we won't be seeing gecko tape in our homes too soon. The medical field will certainly jump at the chance to use a strong, removeable adhesive that doesn't introduce sticky chemicals into the body though. So if gecko tape can be successfully fabricated, would it be possible to make those gloves Tom Cruise is using to climb the Burj Khalifa? Yes! Spiderman can become a reality in the near future. Although while I don't doubt the ability of the gloves to stick to walls, how do you keep said gloves from slipping off your hands...? In the meantime, we've adapted these adhesive And since I mentioned Toad, I need to share with you my favorite superhero science lesson of all time:
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The Biomimetics and Bioinspiration seminar has just concluded with an astounding showing of final projects based on solving problems with water access and quality. We based the project guidelines for the 4th Annual Biomimicry Student Design Challenge. Everyone's work was phenomenal and I must give my gratitude to the great people I had the pleasure to work with: Janne, You, and Jessica. Go team! I wholeheartedly recommend this class to any Temple students reading this, and for anyone outside of Temple to explore the topic more fully! If you found this stuff interesting, I suggest picking up the book that guided our discussions in class and that also had an influence on this blog, The Gecko's Foot. I learned a great deal while researching for class and this blog, and I'm definitely not done yet! My blog will continue to exist and feature bioinspired ideas, but my focus will no longer be exclusively on this. So what will I write about? Well you can always expect more superheroes. I will continue to explore the relationship between science and science fiction with examples from TV (like Star Trek, The X-Files, and Doctor Who) and many many movies. Over the summer, there will be some breakdowns of upcoming blockbusters including, but not limited to, Iron Man 3, Star Trek: Into Darkness, Man of Steel, Pacific Rim, The Wolverine, and The World's End. ...Okay, that last one may not even have any science fiction, but I'm warning you now that I'm going to watch and then constantly talk about this new Edgar Wright film anyway. Other topics will include basically any science that I come across that looks cool which will include lots of marine biology, food science, and inspiration from TED Talks. If you ever feel that I am not including enough comic book-based material, donations of gently used graphic novels and Amazon gift cards will be graciously accepted at the address listed under Contact!
Exploring this new interdisciplinary field was made all the more better with collaboration between biologists and bioengineers. I enjoyed meeting all of these folks very much, and it added a lot to the discussion to have multiple viewpoints! So thank you engineers! For your perspective, for sharing your fancy building with comfy lumbar-supportive chairs, and, most of all, for sharing a ton of free pizza after that one seminar. I have been since informed that this was a rare occurrence and not the norm, but I will continue to dream of a reality where you and I can coexist with piles of pizza, even if we only got to share that one perfect day. The brain is a supervillain's most valuable resource. It schemes, it plans, it designs, and it generates the jealousy or hatred or whatever emotion drives them to commit atrocities. And in the case of some supervillains, it's their only resource! The Lobe is really putting himself out there with a totally unprotected brain atop his body, but at least he HAS a body to help him move that thing around. Some villains are not so lucky either through genetic craziness or tragic accidents. These guys have no bodies, and are organically nothing but superintelligent brain matter. So of course their superintelligence understood the urgency of protecting the little gray cells, and they built robot suits to deal with that. Krang is shown here in what looks like a giant, ugly baby robot suit, and while the Brain always gets a new robot to house his mind after being decapitated by the forces of good, we see him here in only his basic life support chamber. But even in this more vulnerable state, he still has a huge, intelligent, and compassionate gorilla at his side called Monsieur Mallah to take care of him and find him a new robot body. Robotman has a much more slick-looking ride for his lobes (probably because he's actually a superhero, and they need to look good). Don't be fooled by his resemblance to Iron Man, though. There's not a whole human in that suit, just the brain of former racecar driver Cliff Steele. Regular humans are also very committed to protecting our cerebrums and cerebellums! We have the advantage of intact skulls to house our brain matter, but we still need a little help from helmets in contact sports or high speed situations like riding a motorcycle. But there's bad news for humans and supers alike: Helmets don't actually prevent concussions or brain damage! This may sound completely oxymoronic to some people, but it does make sense. Helmets are still extremely successful at protecting your skull, and very valuable because of that. It's much easier to buy a new helmet after the plastic cracks in yours, but harder to fix cracks in your bones. The thing is that helmets only protect the skull. The brain inside still moves around due to the space around it filled with cerebrospinal fluid, and the collisions between your brain and the inside of your skull are what causes concussions. This topic is discussed in a recent Science Friday podcast. So how can nature help us solve this problem? Let's start by taking a look at an animal whose head can withstand 100 times the g-force it takes to give an athlete a concussion without so much as a little dizziness. Scientists have been studying woodpecker anatomy to find out how it can handle such fast deceleration when it's banging its head 20 times a second. The woodpecker is equipped with shock-absorbing spongy layers all around its brain, and a very important section of spongy cartilage between the beak and the skull so some of the impact can be dissipated before it reaches the brain. They also don't have as much fluid around the brain, giving it less wiggle room to move around and hurt itself in confusion. This has inspired special systems of shock absorbers to protect valuable electronics like black boxes in planes or satellite debris falling from space. That's all well and good for electronics, but what about our own neural circuitry? Well, unfortunately we can't change our own skull anatomy to be more like that of the woodpecker (probably), but there is some work being done on more shock-absorbing helmets. One such venture created a cardboard-lined bicycle helmet after the creator suffered a concussion himself while cycling. The cardboard has a honeycomb like structure full of hexagonal cavities that give it strength. The fact that it's made up of cardboard and air makes it very lightweight and relatively cheap to produce. And since the cardboard is made from recycled paper, it's a WAY more environmental cushioning material than the current polystyrene petroleum products used in commercial bike helmets. What a win for bioinspiration! Please protect your heads! References:
Yoon, S.-H., & Park, S. (2011). A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems. Bioinspiration biomimetics, 6(1), 016003. |
Alanna DurkinExploring the realm of biologically inspired design one superhero example at a time, with some other natural sciences mixed in. Archives
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