Manmade materials always come with a catch. Take concrete. It’s impossibly strong, capable of bearing incredible loads that allow us to construct large buildings and even skyscrapers. But at the same time, it’s also quite brittle, which is why it takes nothing more than a midwestern winter to open a massive fissure in a sidewalk.
But now, researchers from Purdue and University of California Riverside have discovered a promising way to make concrete tougher–along with more durable vehicles, helmets, and even batteries. It’s a material inspired by billions of years of evolution that created the micro-architecture hidden inside crustacean shells.
“Every time we go to the lab and make materials, we do a bad job. We increase one property at the expense of another,” says Pablo Zavattieri, a faculty scholar at Lyles School of Civil Engineering. “[Instead] we’re working on one of the main design principles in nature, how to increase a material property without sacrificing other ones significantly.”
For the past decade, Zavattieri has been collaborating with University of California Riverside professor David Kisailus, studying how the biology of living creatures has constructed some of the most impressive materials on Earth. Initially, the team was studying seashells–constructed largely from calcium carbonate (just like our bones), they had impressive material properties. But then, the team came across something even better.
“Basically, as we were studying shells, we found this animal [the mantis shrimp] that can actually punch and break shells with its hammer appendage,” says Zavattieri. “We said, if the hammer can crack open these shells, we should probably study the hammer.”
Researchers learned that the exoskeletons of crustaceans like shrimp, crabs, and lobsters don’t feature any special chemical makeup to become as strong as they are. Instead, they have unique microstructures–layer upon layer of filaments that all run in a single direction–with each subsequent layer rotated slightly. Stacked, the “helicoidal” layers look something like a spiral staircase.
Mechanical engineers already use internal filaments to boost the strength of manmade materials, whether it’s the “fiber” in carbon fiber, or the rebar in concrete, we’ve developed a similar approach to crustaceans already. But what’s different in the case of these exoskeletons is that they feature layers of rotated filaments. Manmade composites generally have just their filaments running in a single direction across the entire material.
In turn, these shrimp-based materials crack differently. When concrete, carbon fiber, or glass crack, the cracks are massive and catastrophic. But by adding helicoidal structures, cracks are essentially blocked from spreading.
“What this architecture does, instead of creating one big crack, it will create many nano or micrometer level cracks,” says Zavattieri. These cracks create what scientists dub as “graceful failure,” or microscopic damage that can absorb impacts without creating system-level structural failure.
For inherently brittle materials like concrete–or what Zavattieri calls “just rocks with cement glue”–helicoidal structures could completely change the known limits of the material. When I ask Zavattieri if we might have concrete that doesn’t crack, he says, “yes, I can imagine that,” though at a minimum, buildings of the future could be far more resistant to earthquakes.
Concrete is particularly promising, in part because you wouldn’t have to add anything to the mix. Instead, 3D printers could shape concrete into micro spirals, making the material tougher by nature. “In another project of mine, we’re 3D-printing concrete,” says Zavattieri. “We could 3D-print houses with this design.”
Meanwhile, the California end of the research team is just experimenting with applying helicoidal principles to materials we use now. Better helmets, components for automobiles, and batteries are all in the works. Batteries are a great example of wear and tear we don’t even see. They break down every time they’re recharged and discharged, as the chemicals inside tear apart the mechanical barriers inside. Helicoidal structures could help batteries be tougher, and last longer, at scale.
Beyond any single use case, however, these helicoidal structures are promising because of their breadth of impact. They’re not unbuildable theory, but something we can already prototype today. “The good news is we can now make these materials. And we can use traditional composite technology to make these designs,” says Zavattieri. “We’re understanding this, and we can apply this to many other cases.”