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Forget whatever you thought you knew about snakeskin, because it ventures into creepier territory than anyone ever thought. It turns out snakes are slimy.
So maybe snakes are not dripping with the ectoplasmic green stuff that Slimer throws around, but they are covered in slime on a nano level. This is what chemist Tobias Weidner of the Max Planck Institute found out when he studied the surface chemistry of snake scales, which revealed that they are not just structurally designed for optimal motion through different environments, but also covered in lipids that that give them that extra slither.
“We wanted to understand the chemistry of the outermost surface of the snake scales,” Weidner, who led a study presented at a recent virtual meeting of the American Chemical Society, told SYFY WIRE. “The composition of the snake tissue is very complex and has lots of different components. We were looking to see which of these components are actually present at the surface, where they play a role for friction and abrasion reduction.”
Snake scales vary in surface chemistry depending on where that species lives and what kind of terrain it has to face. Weidner used laser spectroscopy and electron microscopy to study molecules on snakes whose bodies are in constant contact with surfaces from the ground to tree branches to desert sands. He zeroed in on the layer of molecules at the very top of the skin. These molecules all look spectroscopically similar, which is why surface-sensitive laser and electron methods can tell what kind of species they are observing just from the surface of the scales.
Imagine living on the ground and moving without arms or legs to lift your body; your skin would constantly be rubbing against things. Snakes have lipids with ordered molecules on their undersides, but the lipids on their backs are more disordered since most species’ backs (with the exception of sand snakes) do not need as much protection from friction.
Those on forest floors pass over everything from fallen leaves and twigs to rocks and random lumps, and tree snakes have to contend with abrasive bark. Sand snakes are covered in orderly lipids because they are often completely covered in sand (like the sidewinder, above), especially when they need to burrow underground and cool off in the ruthless desert heat.
“There are one to two single layers on the surface of snakeskin,” Weidner said. “I am guessing the lipids are transported through the skin to the surface. There are lipids present within the scale tissue, and I think it is likely the lipids come from within the scales.”
If we can come up with technology that mimics both the structural and chemical properties of snakeskin, it will be revolutionary in allowing access to places that would have otherwise been impossible to reach before. Rovers that have crawled across the Moon and Mars have always had wheels, but this research could mean a new generation of robots that are able to slide through unexplored cracks in alien surfaces and possibly discover things that were never even imagined to exist. Such robots could also help with searching for ideal locations for lunar and Martian bases. Lava tubes on the Moon are being considered for this—but difficult to explore.
Exactly what kinds of lipids make snakes “nano-slimy”, as Weidner calls it, is still unknown. Both structure and function are needed to create a successful robot (and possibly even wearable materials for humans someday). Think of how a door hinge or bike brake needs to be lubricated to operate smoothly. Snakes need both scales that are highly evolved for their habitats and lubrication to get around. He plans to return to the lab soon and use mass spectrometry, which measures the mass of molecules it takes off from a surface, to determine the types of slime.
“As engineers are making better and better robots mimicking the mechanics of snake locomotion, taking clues from nature and optimizing the robot's surface microstructure and chemistry may help significantly with friction reduction and abrasion protection,” he said.
If scientists were able to decode the structure and function behind the color-changing powers of cephalopods, who knows what might someday be slithering on another planet.