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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.
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