Tag Archives: snakeskin

Similarities between a moth’s eye and snakeskin

Finding patterns in nature that are repeated seems to be the order of the day although there is a twist to this particular story. This time, researchers at Kiel University (also known as, University of Kiel or Christian-Albrechts University of  Kiel [Germany]) have found superficial similarities between a moth’s eye and snakeskin according to a May 4, 2016 news item on Nanowerk,

One thing is obvious: moth’s eyes and snake’s skin are entirely different. Researchers at Kiel University have taken a closer look, however, and have now brought the supposed ‘apples and oranges’ to a common denominator. They have opened up a completely new, comparative view of biological surfaces using a newly developed method, and have thus come closer to the solution of how these surfaces work. Dr. Alexander Kovalev, Dr. Alexander Filippov and Professor Stanislav Gorb from the Zoological Institute at Kiel University have published their findings in the current edition of the scientific journal Applied Physics A (“Correlation analysis of symmetry breaking in the surface nanostructure ordering: case study of the ventral scale of the snake Morelia viridis”).

A May 3, 2016 Kiel University press release, which originated the news item, describes the scientists’ first approach to the research,

One surface demonstrates reduced light reflection, the other is water repellent and resistant to abrasion. Surfaces in the animal world are evolved to adapt to their environments and give the animal they cover the greatest possible evolutionary advantage. Scientists are today still puzzled by exactly how and why these different structures develop in detail.

Current research looks right into the surface nano-structures using the latest research techniques. Normally, we would limit ourselves to comparisons within closely related species and just look thoroughly at small areas of the surface, says Gorb: “That is why we asked ourselves which structural differences can be found between completely different species. To do so, we changed biology’s typical perspective and addressed larger surface areas from various species.” These types of cross-species or cross-material studies of nanostructures are common in other technical or inorganic fields. In Biology, however, this method is completely new, Gorb continues.

They got the idea from the decorations in the hallway of their own institute, where scanning electron microscope images of moth’s eyes and snake’s skin are displayed. At some point, theoretical physicist Filippov noticed similarities between the images, which showed the surfaces at a resolution of a few millionths of a millimetre. Nipples and dimples could be seen which seemed to the human eye to follow a certain pattern. Using methods that are normally used in crystallography, the scientists were finally able to recognise the particular patterns that distinguish the two species. “The structure of moth’s eyes is perfectly organised. Nipples are highly ordered, and preferred directions are exhibited in the structural organisation”, explains Kovalev, biophysicist and main author of the study. The scientists were already aware of the eye structure’s strict symmetry. However, the fact that this goes right through to the nano-level and is repeated across the entire surface in so-called domains, is an important new finding.

So which symmetry does snake’s skin have, which at first glance appears similar, perhaps even more perfectly organised? “Compared to the structure of the moth’s eye, the structure of the snake’s skin is unorganised”, explains Kovalev. He continued: “If we concentrate on one dimple in the skin, like one nipple in the eye, we only see a diffuse cloud of further dimples in the close surroundings. Neither particular directions nor the regular arrangement can be defined. This unorganised structure continues across the entire surface.”

On concluding there were significant differences as well as similarities, the scientists took a closer look,

On their own, these findings about the organised eye structure on the one hand and the unorganised skin structure on the other hand are not especially significant. But by taking the common denominator, i.e. investigating both structures with the same degree of resolution, it is possible for the first time to compare fundamentally different structures, explains Gorb: “However, the ‘coincidental’ degree of organisation is not coincidental, but a result of evolution. That would mean that the perfect organisation gives the moth its incredible night vision, while the imperfect organisation in snake’s skin ensures the best friction properties.” That sounds logical, when you consider the laws of physics, that a symmetrical structure is necessary for good vision and good friction properties require the surface ordering in the contact with the ground to be as low as possible.

If the Kiel-based researchers had followed the usual approaches and compared snakes to snakes and moths to moths, the organisation of the elements at nano-level would have hardly been considered significant. “By comparing evolutionary distant species, we now see that the key to understanding surface functions must be right at the smallest level. Every biological surface is adapted to its environment, and these adaptations are reflected in the organisation of their smallest elements in a certain perfect or imperfect degree”, Gorb concludes.

This is the snakeskin,

Scanning electron microscopy image of the tail ventral scale in the snake Morelia viridis. The black shadowed gray circle marks a typical hexagonal arrangement of dimples, whereas both white and black circles mark five- and sevenfold symmetrical arrangement of dimples, respectively. Credit: research group Gorb

Scanning electron microscopy image of the tail ventral scale in the snake Morelia viridis. The black shadowed gray circle marks a typical hexagonal arrangement of dimples, whereas both white and black circles mark five- and sevenfold symmetrical arrangement of dimples, respectively. Credit: research group Gorb

This is the moth’s eye,

 

Scanning electronmicroscopy image of a single ommatidium surface of an eye in the moth Manduca sexta. Credit: research group Gorb

Scanning electronmicroscopy image of a single ommatidium surface of an eye in the moth Manduca sexta.
Credit: research group Gorb

Here’s a link to and a citation for the paper,

Correlation analysis of symmetry breaking in the surface nanostructure ordering: case study of the ventral scale of the snake Morelia viridis by A. Kovalev, A. Filippov, S. N. Gorb. Applied Physics A March 2016, 122:253 DOI:  10.1007/s00339-016-9795-2 First online: 03 March 2016

This paper is behind a paywall.

Reducing friction with snakeskin-inspired surface

A June 30, 2015 Institute of Physics press release (also on EurekAlert) explains how snakeskin may inspire a whole new generation of robots bound for outer space along with other more earth-bound applications,

Snakeskin-inspired surfaces smash records, providing an astonishing 40% friction reduction in tests of high performance materials.

These new surfaces could improve the reliability of mechanical components in machines such as high performance cars and add grist to the mill of engineers designing a new generation of space exploration robots.

The skin of many snakes and lizards has been studied by biologists and has long been known to provide friction reduction to the animal as it moves. It is also resistant to wear, particularly in environments that are dry and dusty or sandy.

Dr Greiner and his team used a laser to etch the surface of a steel pin so that it closely resembled the texture of snakeskin. They then tested the friction created when the pin moved against another surface.

In dry conditions, i.e. with no oil or other lubricant, the scale-like surface created far less friction – 40% less – than its smooth counterpart.

Lead researcher Dr Christian Greiner said: “If we’d managed just a 1% reduction in friction, our engineering colleagues would have been delighted; 40% really is a leap forward and everyone is very excited.”

Applications are likely to be in mechanical devices that are made to a micro or nano scale. Familiar examples include the sensors in car anti-lock braking systems, computer hard disk drives, and accelerometers in mobile phones, which enable the device to determine for example whether it’s in portrait or landscape mode.

“Our new surface texture will mainly come into its own when engineers are really looking to push the envelope,” Dr Greiner said.

The snakeskin surface could be used in very high-end automotive engineering, such as Formula 1 racing cars. It could also be used in highly sensitive scientific equipment, including sensors installed in synchrotrons such as the Diamond Light Source in the UK or the Large Hadron Collider in Switzerland, and anywhere the engineering challenge is to further miniaturise moving parts.

There is interest in snakeskin-inspired materials from the robotics sector, too, which is designing robots inspired by snakes, which could aid exploration of very dusty environments, including those in space. This raises a new challenge for Dr Greiner’s team: to make a material that decreases friction in only one direction.

Anyone who has felt snakeskin will know that the scales all lie in the same direction and are articulated to aid the snake in its forward motion, while resisting backwards motion. The steel pins tested in this research mimic only the overall surface texture of snakeskin and reduce friction in at least two directions. Dr Greiner has made some progress with polymers that even more closely mimic snakeskin to reduce friction in only one direction. It is, he says, early days and this later work is not yet scheduled for publication.

The only caution is that this new surface doesn’t work well in an environment where oil or another lubricant is present. In fact, the snakeskin effect created three times more friction with lubricant than an equivalent smooth surface.

“This wasn’t a huge surprise,” Dr Greiner explained, “since we were looking to nature for inspiration and the species we mimicked – the royal python and a lizard called a sandfish skink – live in very dry environments and don’t secrete oils or other liquids onto their skin.”

Here’s a link to and citation for the paper,

Bio-inspired scale-like surface textures and their tribological properties by Christian Greiner and Michael Schäfer. Bioinspir. Biomim. 10 044001 doi:10.1088/1748-3190/10/4/044001 Published 30 June 2015

This paper is open access.