Today (8 June) is World Oceans Day. The ocean is an important source for materials, and we are not just talking about ocean plastic or fishing nets that we throw in ourselves. Examples of things from the ocean we use are for example chitin, the main component of the exoskeleton of crustaceans, to make bioplastic, algae and seaweed, or fish leather. And if we don’t take materials out of the ocean, we use the ocean and its inhabitants as inspiration. The shell of the conch, for example, is one of the toughest shells out there. Researchers at MIT are now able to recreate that toughness using 3D printing. Happy World Oceans Day!

The shells of marine organisms have to be strong, to be able to take a beating during storms and tides, rocky shores and sharp-toothed predators. The shells of the conch take it a step further than that. Thanks to its unique structure, it is 10 times stronger than mother of pearl (nacre).

The structure, which is based on 3 different levels of hierarchy. make the shells particularly resistant to fractures. The layers form a zigzag matrix through which the crack has to go in order to spread. This maze makes it hard to do so.

The team at MIT developed a 3D printing technology that replicates this structure. They used composite materials with precisely controlled structures.

To test the relative importance of the three levels of structure, the researchers made variations of the material with different levels of hierarchy. Higher levels of hierarchy are introduced by incorporating smaller length-scale features into the composite, as in an actual conch shell. Sure enough, lower-level structures proved to be significantly weaker than the highest level pursued in this study, which consisted of the cross-lamellar features inherent in natural conch shells.

Testing proved that the geometry with the conch-like, criss-crossed features was 85 per cent better at preventing crack propagation than the strongest base material, and 70 per cent better than a traditional fibre composite arrangement.

This structure could for example be used for helmets and other impact-resistant gear, which require a combination of strength and toughness. Strength refers to a material’s ability to resist damage, which steel does well, for example. Toughness, on the other hand, refers to a material’s ability to dissipate energy, as rubber does. With this new metamaterial, the combination of these two qualities is distributed through the whole material. With 3D printing, the helmets could even be individualised.

Photos: Melanie Gonick/MIT