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If you want to make a better hip replacement, who better to turn to than… a snake? While these hip-less creatures might seem like a weird choice for help with this particular issue, a major part of creating comfortable, long-lasting prosthetics is reducing friction. And few creatures do that better than snakes!

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Sources:
https://phys.org/news/2015-06-snake-skin-surfaces-percent-friction.html
https://iopscience.iop.org/article/10.1088/1748-3190/10/4/044001
https://www.sciencedirect.com/science/article/pii/S1751616117304794
https://drexel.edu/now/archive/2018/May/snake-skin-surface-design/
https://www.sciencedirect.com/science/article/pii/B9780123749765000189
https://iopscience.iop.org/article/10.1088/2051-672X/4/2/024013
https://www.nature.com/articles/srep23539
https://www.sciencedaily.com/releases/2020/06/200601134552.htm

Images:
https://www.istockphoto.com/photo/snake-on-black-background-gm1172268666-325124021
https://www.storyblocks.com/video/stock/snake-crawling-across-sidewalk-handheld-4k-yzsdipu
https://www.istockphoto.com/photo/reticulated-python-gm487506120-73477485
https://www.nature.com/articles/srep23539
https://commons.wikimedia.org/wiki/File:Bitis_arietans_locomotion.gif
https://www.istockphoto.com/photo/snakeskin-pattern-up-close-with-spots-gm452575167-29945246
https://www.istockphoto.com/photo/snake-molt-gm502862090-82124155
https://www.eurekalert.org/multimedia/547685
https://www.eurekalert.org/multimedia/547683
https://www.storyblocks.com/video/stock/a-great-basin-rattlesnake-slithering-in-the-desert-jrm02nn
https://www.storyblocks.com/video/stock/snake-reptile-closeup-hunting-in-rain-forest-diamond-python-hbsz88qalj15zb5z6
https://commons.wikimedia.org/wiki/File:X-ray_of_hips_with_a_hemiarthroplasty.jpg
https://commons.wikimedia.org/wiki/File:Hip_prosthesis.jpg
https://commons.wikimedia.org/wiki/File:Hip_joint_replacement,_United_States,_1998_Wellcome_L0060175.jpg
https://www.istockphoto.com/photo/silver-metal-background-steel-sheet-with-a-brush-pattern-gm866426008-144048405
https://www.storyblocks.com/video/stock/slow-motion-tennis-feet-ready-for-action-bx9joph
https://www.eurekalert.org/multimedia/770987
https://www.eurekalert.org/multimedia/770988
[♪ INTRO].

If you want to make a better hip replacement, who better to turn to than … a snake? While it may seem counterintuitive to look to a hip-less creature for help with this particular issue, a major part of creating comfortable, long-lasting prosthetics is reducing friction.

And few creatures do that better than snakes. By understanding how snakes avoid—and create—friction, engineers are building not just a better hip, but all sorts of everyday items. When you think about it, a snake’s ability to slither is actually pretty amazing.

Evolution has shaped their skin so that they can slip and slide over some of Earth’s roughest landscapes, but, at the same time, give them the grip they need to climb up smooth walls or over slippery rocks. And many species accomplish this without the help of any lubrication. This has to do in part with the way their scales are arranged.

If you’ve ever seen a snake’s skin, you’ll know that the scales all lay in one direction and overlap each other. This creates a flexible, yet continuous surface that helps the snake glide with minimal friction. But they also have to propel themselves along using friction and this piece of the puzzle is invisible to the human eye.

Embedded on their scales are microscopic, hair-like structures called fibrils. The size and shape of the scales, and the positioning of scales and fibrils, gives each snake species its own particular friction profile. For example, large, heavy-bodied snakes like boas and pythons usually move in a straight line.

To do this, they have to lift up part of their body and then thrust themselves forward by pushing against the ground. When engineers took a closer look with a microscope, they found that the parts of the body that push on the ground have more fibrils, giving the snake increased friction in those spots. In other words, those tummy scales aren’t the same all the way along, even though they may look that way to the naked eye.

Snakes make this kind of microscopic study unusually easy by shedding their skin. That allows engineers to easily collect samples from a number of species and use these to map out their scale and fibril patterns, all without disturbing the animal itself. It so happens that snake skins and textured surfaces created in the lab have some things in common, which leads to some pretty clear engineering applications for the lessons researchers are learning.

Both kinds of materials have repeating textures, for example, and a surface roughness that helps create their friction profiles. Snake scales also have a unique spacing, length, orientation and shape that is similar within particular groups of snakes. Similarly, lab-created materials have repeating patterns and protrusions such as cones, dimples and chevrons that are distributed along a surface.

By varying the height, width, and distribution of these features, engineers can design the friction profile they want. But snake skins can still outdo our lab-based materials for example, in the range of conditions in which they can be used. Snakes are able to traverse a variety of terrains without needing to make adjustments to the texture or roughness of their scales.

Whereas engineered surfaces are typically designed for one specific application. Researchers believe that the fibrils are a key component of this. They hypothesize that snakes can essentially modify their friction profile by changing which parts of their undersides, and thus how many fibrils, are in contact with the surface.

So they’ve begun applying what they’ve learned about snake skins to improve upon existing lab-created surfaces. They’re starting out by adding repeating textures to typically smooth items, but they also want to modify existing protrusions on engineered surfaces to mimic these snake fibrils. Which brings us to prosthetic hips.

It’s not really feasible to lubricate a prosthesis that’s inside someone, so reducing friction is key. Existing low-friction hip replacements involve putting a titanium alloy pin with a ball-shaped head in place of the head of the femur bone. The head rotates against a smooth plastic cup-shaped structure inserted in the hip socket.

Even modern prosthetics need some fine-tuning in the friction department, so researchers tested out a new design in the lab. They applied a repeating elliptical texture to the titanium pins mimicking a snake skin pattern. When they slid the titanium alloy pins against heavy-duty plastic discs, the texturized pins reduced friction by nearly half compared to smooth non-textured pins.

And it’s not just hips that are getting improvements! Researchers in Germany used a laser to etch a snake skin-like pattern into the surface of a steel pin. When they moved that pin against another metal surface, they measured a reduction in friction of up to 40% compared to the original smooth, unpatterned version.

The researchers expect their texture could be useful in a wide range of applications, from robotics to Formula 1 race cars. Other researchers are also applying snake skin-inspired techniques to other, more common items, like tennis shoes. But instead of reducing friction like our previous examples, they’re looking to increase friction between the shoe and the ground.

They created shoe grips with a scale-like pattern of cuts that dig into the ground as you step forward, then flatten out again with your foot. Their goal was to reduce slips and falls, which pose a serious risk for older adults, as well as in work-related injuries for people of all ages. All of this is just another reminder of the power of evolution.

Sure, it might have taken millions of years to get there, but nature has already found solutions to many of our trickiest engineering problems. Fortunately, we’re not above a little creative borrowing as engineering works to catch up! Thanks for watching this episode of SciShow, and thanks as always to our patrons for helping us make it happen.

If you’d like to get involved, you can get started at patreon.com/scishow. [♪ OUTRO].