SeaShells have something to teach us

A Scanning Electron Microscope (SEM) image of the region surrounding an indentation the researchers made in a piece of shell from Placuna placenta. The image shows the localization of damage to the area immediately surrounding the stress. Credits: Ling Li and James C. Weaver

Quite often I post news on researchers looking at Nature to solve problems, and this is just another one.

At the MIT researchers wanted to understand why the materials we are manufacturing to use as shields for protection tend to loose their strength after having been subjected to a localised trauma. Thinks about a windshield of a car. It is quite robust but if a pebble hits it does not just create a tiny dent on the impact point, chances are that the whole windshield, immediately or over days and week, will transform into a web of broken glass. Injuries spread around.

Not so in the case of seashells. A traumatic impact on the shell may break it where the impact occurs but does not diminish the overall strength.

By analysing at the electron microscope the deformation at the point of impact researchers have seen that the nano-deformation of the structure are self protecting one another so that the damage goes not expand. Additionally, they have seen that the way the molecules are organised lead to a high dissipation of energy that is what you want to have to keep the damage localised.

The material of the shell (mostly calcite) changes its structure as the impact strikes through a process called twinning where each crystal breaks up into a pair of symmetrical regions forming a sort of dam that keeps damage locally. Interestingly this not just preserves the robustness of the material on the global scale, it also preserve its transparency (if the material is transparent to start with). 

Now the plan is to replicate these nanostructure in artificial materials to get the same kind of characteristics.

Author - Roberto Saracco

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