The amazing variety of living species with which we share the planet have had millions, or even billions, of years to hone their functional designs, and because of that, sometimes they’re just smarter than we are. We still have so much to learn from them, and that’s one of the main reasons it’s so important to preserve the wide array of animals and plants around us and not to take them for granted.
Latest case in point: stronger and lighter bridges! Actually also buildings, spacecraft, and a bunch of other things, too.
The humble deep-sea sponge Euplectella aspergillum (or Venus’ flower basket) has been found in a study published this week by Matheus Fernandes and other Harvard researchers to have a significantly better design than we’ve historically been using for light but strong lattices that don’t buckle under stress.
Let’s start with the trestle bridge. It’s basically a big lattice that has to bear a lot of weight, and we want to build it using as little material as we can, arranged in a network pattern that makes it strong. For centuries, right up to this day, we’ve used a couple of main designs for that. There’s the simple crosshatch, for when the weight load is not so great:
And for larger stresses, such as supporting cars or trains, we have the reinforced crosshatch, or repeated squares with X’s in them. A good example is the Kinsol Trestle Bridge in British Columbia, the world’s tallest wooden trestle bridge, completed 100 years ago. A material that’s just OK (wood) can hold up really well if arranged the right way:
We see the same type of lattice used in modern steel trestle bridges as well:
Even Thomas and Friends know about this ubiquitous design:
It’s long been anecdotally known that the skeleton of the Venus’ flower basket is lightweight and strong, and it also has an eye-catching lattice design:
Magnifying this up to see the basic structure:
And translated to a regular lattice design for practical use:
If you 3-D print some lattices, you can compare their strength for practical applications by measuring how hard you have to press down on them before they buckle. Here’s how a few designs look before and after you’ve compressed them by 6%. A is the sponge lattice, B is a simpler design based on the sponge lattice, C is our typical Thomas trestle lattice, and D is just a plain crosshatch:
The key, of course, is how hard you have to push down to get compression. Each will gradually compress as you push, but each has a certain point — the critical stress — at which it’ll just buckle. Then it suddenly gets much easier to compress, so that’s like, bridge collapse. You can tell just by looking that design D is already in big trouble; it’s not going to take much more force to squish that one.
So how does design A (from the sponge) hold up compared to the others? Here’s a graph that shows how hard you have to push each design to get it to buckle, or the critical stress. The angle theta (θ) is the angle at which you’re pressing: 0 degrees is pressing straight down, as you would on a trestle bridge, while 45 degrees would be pressing on a corner of the 3D-printed square.
Design A is easily the best, no matter what angle the pressure comes from. All hail the sponge!
In fact, they went on to do computer simulations with many other designs (without actually constructing all of them) and found that the absolute optimum turned out to be just a slight variation on the sponge lattice, with diagonals placed a teeny bit wider, and having a critical stress only about 9% higher. So the naturally occurring sponge lattice is darn close to optimal.
Here’s what the totally, totally optimum design looks like (they did print this one up and test it to make sure their calculations panned out), in case you’re about to build your own trestle bridge:
So Venus’ flower basket has shown us how to use the same amount of material and yet get a bridge, skyscraper, or spacecraft with a structure that’s 30-40% stronger.
It had already been known, by the way, that the clear silica (basically glass) fibers that Venus’ flower basket anchors itself to the seabed with not only have light-propagation properties that equal or exceed those of optical fibers currently in use, but can also bend much further than conventional glass fibers before breaking. That’s at least two other cool things this organism is teaching us.
Not bad for a euplectellid.