Gecko adhesion has its own molecular structure: where gecko feet are covered in a super-thin layer of lipids that help them stay sticky
Gecko feet are famous for being grippy and sticky, allowing them to scale vertical surfaces with ease. Researchers find that this tactic is developed from millions of microscopic, hairlike structures on their toes.
After zooming in on these ‘setae’ structures, researchers from the National Institute of Standards and Technology (NIST) found that they are coated in an ultra-thin film of water-repelling lipid molecules – which are only one nanometer, or billionths of a meter thick.
Hydrophobic lipids that repel water
Analysing the surface of the setae using high-energy X-rays thrown off by a type of particle accelerator called a synchrotron, the synchrotron microscope showed that the lipid molecules line the surface of the setae in dense, orderly arrays.
Lipids molecules are hydrophobic, meaning they repel water, which can allow the small creature to climb to high heights without being affected by any liquid on surfaces.
Physicist and co-author Tobias Weidner of Aarhus University in Denmark, said: “The lipids might function to push away any water beneath the spatulae, allowing them to make closer contact with the surface. This would help geckos maintain their grip on wet surfaces.”
“The lipids might function to push away any water beneath the spatulae. Allowing them to make closer contact with the surface”
Similar proteins to those found in human hair and fingernails, the setae and spatulae are made of a type of keratin, which are extremely delicate.
Keratin fibres are aligned in the direction of the setae, which might help them resist abrasion too.
Setae provide sticking power because they are flexible and assume the microscopic contours of whatever surface the gecko is climbing.
Even smaller structures at the ends of the setae, called spatulae, make such close contact with the climbing surface that electrons in both materials interact, creating a type of attraction called van der Waals forces.
To release its foot, which might otherwise stay stuck, the gecko changes the angle of the setae, interrupting those forces and allowing the animal to take its next step.
Geckos have inspired many products, including adhesive tapes with setae-like microstructures
Biologist and co-author Stanislav Gorb of Kiel University in Germany, said: “The most exciting thing for me about this biological system is that everything is perfectly optimized on every scale, from the macro to the micro to the molecular. This can help biomimetic engineers know what to do next.”
NIST physicist and co-author Dan Fischer, added: “You can imagine gecko boots that don’t slip on wet surfaces or gecko gloves for holding wet tools. Or a vehicle that can run up walls, or a robot that can run along power lines and inspect them.”
A better understanding of the molecular features of setae might lead inventors who find inspiration in nature, a concept called ‘biomimicry’, to come up with even better innovative designs.
The NIST synchrotron microscope that the researchers used to evaluate the setae can identify molecules on the surface of a three-dimensional object, measure their orientation and map their position. It is also a half-mile-long particle accelerator that provides a source of high-energy X-rays for illumination.
This microscope is typically used to understand the physics of advanced industrial materials, including batteries, semiconductors, solar panels and medical devices – but a better understanding of the molecular features of setae might lead inventors who find inspiration in nature, a concept called ‘biomimicry’, to come up with even better innovative designs.
Fischer said: “But it is fascinating to figure out how gecko feet work, and we can learn a lot from nature when it comes to improving our own technology.”
