Joe Tully
05-22-2002, 01:32 PM
I found this page that goes into the ability of geckos to climb walls. I thought it was interesting so I figured I'd post it here.
http://beyond2000.com/news_archive/story_656.html
After the shattering earthquake, trapped in a ruined and dusty basement, you'll probably feel quite lonely. As time drags on you'll more and more concerned that nobody will ever find you. How could any human even crawl down there? Just as despondency sets in you'll become aware of something moving across the roof. In the feeble light of your torch you spot a mechanical flash bolting rapidly across your improvised ceiling. It freezes; a tiny robotic lizard hangs by one foot from the wall, gravity seemingly no obstacle to its wanderings. Again it bursts into action, scurrying down the damp stone wall to halt in front of your face. You'll know then that rescue is indeed very close as you peer into the beady camera-eyes of gecko-bot, the world's most talented climber. He'll get the message through!
This disaster and robot scenario is fictional…for the moment. However, the remarkable climbing abilities of living, breathing geckos are certainly real. The tiny tropical lizards can dash up a polished glass wall at a meter per second. They can even do it upside down. Not all their feet are necessary either; they can hang their entire body weight from a single toe. Published in this week's issue of Nature, an investigation into the sticky feet of this saurian acrobat reports the first direct measurement of the adhesive function that makes it possible for it to master these amazing feats.
The discovery is inspiring engineers to design tiny, climb-anywhere robots that may one day aid search and rescue missions, and also to create the world's first dry, self-cleaning glue that will work in space and even under water.
Biologists Kellar Autumn of Lewis and Clark College and Robert Full of UC Berkeley took a very close look at the footpads of the speedy tropical reptiles and found that when it comes to defying gravity, the Force is with them.
Fractal Footsies
On the underside of their feet, Autumn explains, geckos have millions of seta; microscopic hairs that function as an adhesive. The length of these tiny setae is only equivalent to the width of two human hairs laid side by side: roughly 1/10 of a millimetre. But these minuscule structures are not the end of the story…or the foot. At the tip, each seta divides into about 1,000 even tinier pads. These projections, called spatulae, are so small they span less than the wavelength of visible light.
It is the spatulae that are the secret to the gecko's climbing talents. The biologists theorise that the protuberances get so close to a surface that weak interactions between molecules in the pad and molecules in the wall actually become significant. The combined attraction of a billion pads is a thousand times more than the gecko needs to hang on the wall.
Using a nanoscopic force sensor designed by Thomas Kenny of Stanford University and an ultra-fine aluminium wire, the scientists took a single seta from a Tokay gecko (Gekko gecko) and measured the diminutive forces of adhesion for the first time.
"We got a nasty surprise when we tried to touch the end of the hair to a surface," Autumn says. "It wouldn't stick. But when we manipulated it in a particular way, simulating the movements of a gecko's foot, we discovered that the seta is 10 times more adhesive than predicted from prior measurements on whole animals," Autumn said. The strength of attachment is great enough that the single gecko hair could pull and bend the aluminum wire. "In fact, the adhesive is so strong that a single seta can lift the weight of an ant. A million setae, which could easily fit onto the area of a dime, could lift a 20-kilo child. Our discovery explains why the gecko can support its entire body weight with only a single finger."
"Geckos have developed an amazing way of walking that rolls these hairs onto the surface and then peels them off again, just like tape." Full says.
Autumn adds, "Getting yourself to stick isn't really that difficult. It's getting off the surface that is the major problem. When a gecko runs, it has to attach and detach its feet 15 times a second.
Of walls and Waals
Biologists had always assumed that geckos used suction cups or a chemical secretion to stick themselves to vertical surfaces, but the team found this wasn't the case. The setae were much more efficient than pure suction, and besides, geckos can even stick to walls in a vacuum. Also, there is no evidence that geckos use glue: they have no glue glands on their feet, nor is glue residue left on the surface. The hairs do not interlock with the surface, as with Velcro, nor is friction a credible explanation. (Friction could not explain their ability to walk on the ceiling.) Electrostatic attraction was ruled out by other researchers.
So how do the setae work? "We believe that the seta sticks using only intermolecular forces," Autumn said. "These are weak electrodynamic forces that operate over very small distances."
"The intermolecular forces come into play because the gecko foot hairs get so close to the surface," Full says. "The hairs allow the billion spatulae to come into intimate contact with the surface, combining to create a strong adhesive force."
The likely methodology involves a mysterious influence known as the Van der Waals force. This is among several types of intermolecular forces that are weak until surfaces get very close. When a large area is in contact though, they can add up to a strong attraction. Van der Waals forces are responsible for the attraction between layers of graphite, for example, and the attraction between enzymes and their substrate.
Our calculations show that van der Waals forces could explain the adhesion", reports Full.
Sticky in strange places
Besides this magic molecular sticking power on sheer surfaces, the scientists discovered that the gecko adhesion works under water, leaves no residue and is self-cleaning. The scientists clogged the gecko hairs with debris, but five steps later, and completely inexplicably, the hairs were clean.
All of those involved in the lizard tests foresee countless applications for a synthetic gecko adhesive, from vacuum areas of clean rooms to space construction. Currently a number of the engineers are working to design and fabricate artificial gecko setae. If they succeed the world will have uts first dry, self-cleaning glue."
Work is also underway in conjunction with IS Robotics in Boston to design tiny robots that can climb on walls and even upside down. Gecko-based bots might be useful in search and rescue missions, underwater landmine clearance and any environment where standard locomotion presents difficulties. So far the work has resulted in a mechanical lizard that adopts the peeling action of geckos to walk on vertical surfaces. At the moment though, the small robot uses an adhesive glue to stick. Synthetic, nanoscopic setae will yield a much better and longer lasting robot machine.
You can also see testing of a prototype Geckobot at http://www.me.berkeley.edu/hel/Gecko.htm
Click the link there for a video file.
It has links on the side to intersting pics...Robo-Snakes, Robo-Frogs...
Here's a pic of a more recent Gecko-bot, that can climb completely vertical surfaces.
http://polypedal.berkeley.edu/PPLab_gifs/image145.gif
http://beyond2000.com/news_archive/story_656.html
After the shattering earthquake, trapped in a ruined and dusty basement, you'll probably feel quite lonely. As time drags on you'll more and more concerned that nobody will ever find you. How could any human even crawl down there? Just as despondency sets in you'll become aware of something moving across the roof. In the feeble light of your torch you spot a mechanical flash bolting rapidly across your improvised ceiling. It freezes; a tiny robotic lizard hangs by one foot from the wall, gravity seemingly no obstacle to its wanderings. Again it bursts into action, scurrying down the damp stone wall to halt in front of your face. You'll know then that rescue is indeed very close as you peer into the beady camera-eyes of gecko-bot, the world's most talented climber. He'll get the message through!
This disaster and robot scenario is fictional…for the moment. However, the remarkable climbing abilities of living, breathing geckos are certainly real. The tiny tropical lizards can dash up a polished glass wall at a meter per second. They can even do it upside down. Not all their feet are necessary either; they can hang their entire body weight from a single toe. Published in this week's issue of Nature, an investigation into the sticky feet of this saurian acrobat reports the first direct measurement of the adhesive function that makes it possible for it to master these amazing feats.
The discovery is inspiring engineers to design tiny, climb-anywhere robots that may one day aid search and rescue missions, and also to create the world's first dry, self-cleaning glue that will work in space and even under water.
Biologists Kellar Autumn of Lewis and Clark College and Robert Full of UC Berkeley took a very close look at the footpads of the speedy tropical reptiles and found that when it comes to defying gravity, the Force is with them.
Fractal Footsies
On the underside of their feet, Autumn explains, geckos have millions of seta; microscopic hairs that function as an adhesive. The length of these tiny setae is only equivalent to the width of two human hairs laid side by side: roughly 1/10 of a millimetre. But these minuscule structures are not the end of the story…or the foot. At the tip, each seta divides into about 1,000 even tinier pads. These projections, called spatulae, are so small they span less than the wavelength of visible light.
It is the spatulae that are the secret to the gecko's climbing talents. The biologists theorise that the protuberances get so close to a surface that weak interactions between molecules in the pad and molecules in the wall actually become significant. The combined attraction of a billion pads is a thousand times more than the gecko needs to hang on the wall.
Using a nanoscopic force sensor designed by Thomas Kenny of Stanford University and an ultra-fine aluminium wire, the scientists took a single seta from a Tokay gecko (Gekko gecko) and measured the diminutive forces of adhesion for the first time.
"We got a nasty surprise when we tried to touch the end of the hair to a surface," Autumn says. "It wouldn't stick. But when we manipulated it in a particular way, simulating the movements of a gecko's foot, we discovered that the seta is 10 times more adhesive than predicted from prior measurements on whole animals," Autumn said. The strength of attachment is great enough that the single gecko hair could pull and bend the aluminum wire. "In fact, the adhesive is so strong that a single seta can lift the weight of an ant. A million setae, which could easily fit onto the area of a dime, could lift a 20-kilo child. Our discovery explains why the gecko can support its entire body weight with only a single finger."
"Geckos have developed an amazing way of walking that rolls these hairs onto the surface and then peels them off again, just like tape." Full says.
Autumn adds, "Getting yourself to stick isn't really that difficult. It's getting off the surface that is the major problem. When a gecko runs, it has to attach and detach its feet 15 times a second.
Of walls and Waals
Biologists had always assumed that geckos used suction cups or a chemical secretion to stick themselves to vertical surfaces, but the team found this wasn't the case. The setae were much more efficient than pure suction, and besides, geckos can even stick to walls in a vacuum. Also, there is no evidence that geckos use glue: they have no glue glands on their feet, nor is glue residue left on the surface. The hairs do not interlock with the surface, as with Velcro, nor is friction a credible explanation. (Friction could not explain their ability to walk on the ceiling.) Electrostatic attraction was ruled out by other researchers.
So how do the setae work? "We believe that the seta sticks using only intermolecular forces," Autumn said. "These are weak electrodynamic forces that operate over very small distances."
"The intermolecular forces come into play because the gecko foot hairs get so close to the surface," Full says. "The hairs allow the billion spatulae to come into intimate contact with the surface, combining to create a strong adhesive force."
The likely methodology involves a mysterious influence known as the Van der Waals force. This is among several types of intermolecular forces that are weak until surfaces get very close. When a large area is in contact though, they can add up to a strong attraction. Van der Waals forces are responsible for the attraction between layers of graphite, for example, and the attraction between enzymes and their substrate.
Our calculations show that van der Waals forces could explain the adhesion", reports Full.
Sticky in strange places
Besides this magic molecular sticking power on sheer surfaces, the scientists discovered that the gecko adhesion works under water, leaves no residue and is self-cleaning. The scientists clogged the gecko hairs with debris, but five steps later, and completely inexplicably, the hairs were clean.
All of those involved in the lizard tests foresee countless applications for a synthetic gecko adhesive, from vacuum areas of clean rooms to space construction. Currently a number of the engineers are working to design and fabricate artificial gecko setae. If they succeed the world will have uts first dry, self-cleaning glue."
Work is also underway in conjunction with IS Robotics in Boston to design tiny robots that can climb on walls and even upside down. Gecko-based bots might be useful in search and rescue missions, underwater landmine clearance and any environment where standard locomotion presents difficulties. So far the work has resulted in a mechanical lizard that adopts the peeling action of geckos to walk on vertical surfaces. At the moment though, the small robot uses an adhesive glue to stick. Synthetic, nanoscopic setae will yield a much better and longer lasting robot machine.
You can also see testing of a prototype Geckobot at http://www.me.berkeley.edu/hel/Gecko.htm
Click the link there for a video file.
It has links on the side to intersting pics...Robo-Snakes, Robo-Frogs...
Here's a pic of a more recent Gecko-bot, that can climb completely vertical surfaces.
http://polypedal.berkeley.edu/PPLab_gifs/image145.gif