I’m gonna guess you don’t see a lot of chainmail walking around these days.

Unless you’re at a Renaissance faire. Or a particularly avant garde fashion show.

Or that like one specific  Chappell Roan performance… Okay, maybe we’re seeing a bit more chainmail now than we were a few decades ago. And it turns out, even science  can’t escape the trend. Because one team of researchers recently developed a sort of 3D chainmail.

And their invention has  some really weird properties that the laws of physics can’t completely explain. [ intro jingle ] These days, we mostly use chainmail in things like kitchen gloves and  shark-protecting diving suits. But the oldest examples  date back to around 300 BCE. For example, you may have seen depictions of the Roman lorica hamata, which was probably borrowed  from early Celtic designs.

In Europe, chainmail stayed  popular for more than a millennium. Around the 14th century, it started getting replaced by suits of armor But it stuck around in other parts of the world, like Persia and India, for even longer. And I can kind of see why.

It’s great at protecting  you against slashing damage. So it’d be a critical defense for anyone living In a predominantly sword-based fighting culture. But I can also see why chainmail  eventually got replaced.

For one thing, it wasn’t super  great against piercing damage, on account of the many many open spaces. So, it was pretty vulnerable to things like stiletto daggers and arrows. Also, because it’s basically two-dimensional, a layer of chainmail wasn’t  amazing against bludgeoning damage.

See, the reason it hurts when something hits you … be it a fist or an unrealistically large hammer … is that the collision transfers  energy from that something to you. And if an unrealistically large hammer smashes against just one sheet of what is effectively a heavy duty fabric, the energy is not going to be absorbed or redirected in a way that keeps it away from what’s sitting underneath that fabric. By which I mean your fleshy body.

Now, to be fair, chainmail is better at  preventing blunt force trauma than, say, a cotton denim jacket. The fact that all those interlocked rings can move around relative to one another means they can disperse  some of the incoming energy. Just not a ton.

But what if we thickened all that up? If you pad out your body in foam  and have your friend punch you, it’s gonna hurt a hell of a lot less than getting punched in your t-shirt. The air pockets in the foam  allow it to deform for a bit, and dissipate energy before  it gets through to the wearer.

So foam is pretty protective. But 3D chainmail would be even better. For one, it would inherently  be made of tougher stuff.

For another, it’d be a lot easier to move in. And by virtue of there being  a bunch of interlocked links, each link has more axes of movement relative to the others it’s attached to. That allows for even more ways  to absorb and disperse energy.

But to discover all the cool  and potentially weird properties that come from turning chainmail 2D into 3D, you have to actually make it … And then do a bunch of  experiments with what you made. Which leads me to a team of Caltech researchers who invented something called PAMs. But before I tell you about that, a quick ad.

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A. K. A. polycatenated  architected materials.

Which if you speak the right  dialect of science jargon, tells you exactly what’s going on. “Poly” means “many”, “caten” refers to chains, and “architected materials”  are specific structures made of repeating cells with connecting tissue. So, “polycatenated architected materials” means “lattice-like material  built of many chains.” That sure sounds like 3D chainmail to me. If you look at any of these PAM blobs, they seem pretty darn simple.

But the design process was a bit more complicated than just “Make chainmail, but more!”. The team started by modeling  a solid crystalline lattice. In other words, a solid  made of individual particles connected by strong, rigid bonds.

Like this. Then, they went into that structure  and replaced all the particles with what are basically tiny  cages linked loosely together, instead of being connected by stiff bonds. This added a whole bunch of degrees of movement to the overall material.

Finally, they printed out a  bunch of spheres and cubes measuring about 5cm across. The PAMs were made of different materials, like acrylic and nylon. And the cages took all kinds of shapes… mostly circular, but also some more pyramidal or hexagonal designs.

With a bunch of physical samples, the real experimentation could begin. The team tested how each of their PAMs would react to an assortment of  forces, focusing on three primary ones: Compression, or squishing force. Torsion, or twisting force.

And sheer, or sliding force, like the force of water passing over a riverbed. During those tests, the team  discovered something pretty cool. When the PAMs were being compressed, they behaved like a solid and stood firm,  rather than squishing out of the way.

But under shear forces, they behaved like a liquid,  and flowed around obstructions. And the point where the PAMs fully  transitioned between “solid” and “liquid” depended not just on what  forces were acting on them, but also how they were printed. Like, nylon PAMs worked  differently than metal PAMs, and round cages worked differently  than prism-shaped ones.

This sometimes solid, sometimes liquid property can  be found elsewhere in nature. And I’m not like talking about a cat  taking up its bowl that it’s sitting in A big mass of sand can act  both like a solid and a liquid, because the individual grains  can flow over one another. Or think back to your childhood  playing with oobleck … that mix of cornstarch and water.

If you slap it, it feels solid. But if you slowly stick your finger in, it’s just a thick liquid. All these examples might make you  think the scientists behind PAMs understand what’s going on.

But there’s actually entirely new physics needed to explain how they work. Because a lot of the theories we  have can only apply sometimes. For example, the kinetic theory of granular materials works when a shear force is applied at, like, a slow to medium rate.

But it doesn’t apply when the PAMs are already under a lot of compression. So researchers will have to continue  playing with their 3D chainmail in a scientifically rigorous way. But once we eventually  understand them a little better, these materials could have a  huge number of applications.

Remember the whole foam discussion? All the extra degrees of motion  that make PAMs even better at energy absorption than  foam could make them ideal for protecting fragile objects. Like, a football player’s head.

And if scientists learn how  to miniaturize the technology, the fact that PAMs can change shape and flow like liquid could make them excellent candidates for protecting our bodies from the inside. Early experiments with microscopic PAMs show that they can respond to electric charge, which may allow us to  control their shape remotely. So one day, scientists could  design some kind of PAM robot that squishes itself into the  right spot in a patient’s body, fixes whatever it can, and then squishes out.

No invasive procedure required! In the meantime, I’m sure someone out there  is already thinking of ways to turn this new kind of chainmail  into a fashion statement. Or at least a desk toy. [Outro]