Scientists Discovered What Makes Coral Cities So Strong—and Want to Copy Their Blueprint

3 min read

Here's what you'll learn when you read this story:

• Corals have been around for hundreds of millions of years, and the skeletons they build from calcium carbonate are both complex and resistant to damage.
• Researchers dove deep into how these sea creatures use calcium carbonate to biofabricate entire underwater cities and analyzed how 3D-printed recreations compare.
• While we still haven't replicated the toughness of coral skeletons, 3D printing and other methods of producing these structures offer sustainable solutions for the future.

Some technical innovations appeared long before human beings ever walked the Earth. Over 500 million years ago, corals began creating complex ecosystems that exhibited mechanical properties to rival anything made by humans eons later. Corals were essentially prototypes for 3D printers, biofabricating impressive skeletal structures capable of forming a metropolis on the ocean floor.

Around 247 million years ago, during the same period that witnessed the emergence of the first dinosaurs, Scleractinian corals diverged from their Cambrian ancestors. These corals look like alien flowers, but they're actually cnidarians related to jellyfish and anemones. They make up the majority of Australia's Great Barrier Reef, which is so large that it was famously observed by ESA's Envisat (Environmental Satellite) from almost 500 miles (800 km) above in 2012, and later photographed and filmed from the International Space Station.

What makes scleractinian (“hard rayâ€) corals special is that they're the main type of anthozoan (‘blooming animal') capable of synthesizing a massive mineral skeleton that remains after they die and their soft bodies dissolve. Scleractinian corals also mineralize faster than most marine organisms, gathering free-floating calcium and carbonate ions from the surrounding water to create chalky skeletons on top of older skeletons. Yet exactly how they do this hasn't been well understood. Now, an international team of researchers wants to leverage what they found out about the building abilities of these corals to potentially replicate it in the human sphere.

“Coral skeletal material exhibits exceptional precision, structural organization, and impressive mechanical properties, durability, and resilience against fractures, making it valuable for various applications in a range of sectors, from biomedical to engineering,†they said in a study recently published in Advanced Materials.

Besides calcium carbonate, corals form the crystalline microstructures of their skeletons using proteins, lipids and sugar molecules known as glycans. Lipids are involved in the growth and arrangement of skeletal crystals, while glycans shape growth by mediating interactions between minerals and the entire matrix. Corals also use proteins high in acid to create crystals and select variants of calcium carbonate, especially aragonite, that form radiating crystal clusters. What's really astounding is that corals merge their mineral and organic aspects into materials with properties that are equal and even superior to those of synthetics. There's one type of skeletal material that's ten times stronger than concrete and still twice as strong as reinforced concrete. Other materials are highly resistant to fractures.

There have been previous attempts at replicating the properties of coral through 3D printing and other methods. One research team tried printing a mixture of calcium carbonate and resin into complex structures using photopolymerization, a process that uses light to link monomers together into polymers. While the structures appeared remarkably like corals, the mechanical properties were not all there, and it wasn't clear how to avoid shrinkage, mitigate cracking, and pull off manufacturing the stuff across multiple scales. Another, more sustainable method converted calcium carbonate into crystalline forms, then added a magnesium ion to turn them into aragonite ceramics. The mechanical properties of this material were comparable to actual corals.

Another approach involves replicating corals by creating a living system in which microbes and engineered cells biomineralize calcium carbonate. The advantage of using live organisms is that they can grow and heal themselves with some help from scaffolds and synthetics. Although this process is slow and can only be done on a small scale so far, biomimicry may be the solution to fabricating coral-like materials. With this strategy, which can be easily adjusted and controlled, organic materials are used to mimic the carbonate chemistry corals use for their skeletons by capturing calcium carbonate molecules and forming crystals with them.

“Harnessing this interconnected multiscale, parallelized biotechnological framework for manufacturing CaCO3 and other (bio)materials could yield significant advancements,†the researchers said, “[both] in biomimetic designs and sustainable approaches to material engineering.â€

Someday, it might be possible to create entire self-building cities above water, but for now, that's all still in the realm of science fiction.

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Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.