Uncovering the Hedgehog’s Secret Superpower
And What That Means for the Future of Impact Protection
As a hedgehog goes about its day, it will face a point where the only option it has is to take a leap of faith off a 30 ft. tall oak tree.
Wait, hold up. What??
No, this isn’t some animal cruelty documentary. Wild hedgehogs are actually known to climb way up high in search of food (little wormies being the snack of choice). Being out there in the open is vulnerable making them easy targets for birds of prey.
Instead of tediously climbing back down to escape their feathered predators, they just fall (all 30 ft!), with no trampoline needed. ↓ At least, no external trampoline.
Built in Cushion
Spiky spines might seem like the opposite of a cushion, but for hedgehogs they do the trick.
When a hedgehog lands on the ground, its spines knock into each other setting off a domino effect throughout its pelt. This absorbs the impact by distributing the force of the fall over a large surface area, or at least as large as a hedgehog is ;)
Imagine a toothbrush. If it’s dense with bristles, it’s hard to push against. But, if there are only a few you’ll easily be able to push them down and touch the plastic head. Which one do you think provides more protection?
The more dense the toothbrush is with bristles, the better protected the head is because of all the extra resistance. That’s why hedgehogs have over 5,000 spines, to distribute the force.
Only having the spines press against each other wouldn’t be enough to keep them safe though. It might work once, but afterwards the spines would be all bent and broken. Besides their layout, hedgehog spines have an internal structure of air chambers. This allows them to resist buckling under their axial load (force applied to the tip) 3 times better than a hollow tube would.
We know how classy hedgehogs like to be, so there’s no way they would settle for plain straight-sided chambers. No, they got fancy with some flower shapes. 🌸
There are 22 stringers running up and down the inside of the spine.
Intersecting the stringers are plates that branch off into 3 separate plates before connecting with the wall. This results in many many many small chambers.
Comparing a spine to a 201 stainless steel rod of the same diameter, the spine would come out stronger! But not only that, hedgehog spines are also as pliable as styrene rods with a slightly larger diameter.
Okay, this is great, but what does this mean for us? Like why should anyone except the bird mafia care? 🐦
Well imagine if humans could do what hedgehogs could. Or protect our objects to go through the same. We would be superpowered! Car crashes would be less deadly, transport cases wouldn’t need extra padding, and our stunt doubles would be performing their most daring tricks yet.
When I was four, I got a concussion from falling 5 feet. If my flooring had had hedgehog inspired spines underneath it, would I still have gotten hurt? Maybe, but maybe not.
Obviously things aren’t that simple for hedgehog protection to become mainstream. We’re not as experienced as hedgehogs, so making something so intricate on a commercial scale is difficult. 3D printing isn’t feasible enough yet and injection molding can’t make enclosed chambers.
Our advantage over hedgehogs is that we don’t need to do everything that hedgehogs do. Not every part of a spine is designed for impact protection because however fun it might be, hedgehogs do not spend all of their time on the big tree drop tower.
This means we can simplify the internal structure when mimicking spines without affecting how well they function.
The startup Hedgemon has figured this out and is creating a hedgehog inspired football helmet liner to prevent concussions. They’re super cool and I recommend you check them out!
If you skipped straight down here or are a visual learner, here’s a video that explains pretty much the same thing. 🎥
If you’d like to learn more about hedgehogs and what their spines can teach us, take a look at this one-pager. 📄
If you want to make your own 3D model of a spine, follow my Solidworks tutorial. 💻
Finally, these are two great papers for you to read:
Static flexural properties of hedgehog spines conditioned in coupled temperature and relative…
We analyze the flexural strength and modulus of hedgehog spines. * Hedgehog spine flexural properties are tunable based…
Hey I’m Klara, a 14 yo Innovator at TKS. If you want to learn more about the projects I’m doing in biomimicry, be sure to follow me here on Medium, connect on LinkedIn, or get in touch with me at email@example.com! Also subscribe to my newsletter to get monthly updates on what I’ve been up to and cool resources I’ve found! ✌