#worldoceansday How marine organisms create super tough skeletons

08-06-2022

Marine organisms are experts in engineering.  After decades of research on them, a team from Technion – Israel Institute of Technology has discovered the mechanisms the creatures use to create extremely tough structures through biomineralisation.

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For decades, scientists have searched inspiration in nature for the development of new materials or the improvement of existing ones. Oceans and its inhabitants can teach us a lot about innovative, super strong structures.

A team from Technion- Israel Institute of Technology, together with scientists from different beamlines at the ESRF, has found how different organisms, namely algae, corals, sea urchins, starfish or brittle stars, can create a super hard skeleton through the process of biomineralisation. The collaboration with the ESRF led the team to carry out experiments using different techniques, such as X-ray powder diffraction and micro- and nanotomography (beamlines ID22, ID19 and ID16B, respectively) to investigate the specimens at different length scales.

The way they do this is by depositing calcite particles in magnesium-poor substances to create compression in the organisms’ skeletons that increase their rigidity. Each organism studied has a slightly different strategy to reach toughness.

Lessons from the brittle star

The brittle star Ophiomastix wendtii, which lives in coral reefs, has hundreds of super resistant focal lenses made of chalk on its arms.

How does this creature make brittle material durable under natural conditions? Thanks to the experiments at the ESRF, the researchers discovered that the crucial stage in the process of lens formation is the transition from the amorphous phase – the phase between liquid and solid – to the crystalline phase. At this stage, calcite nanoparticles, which are rich in magnesium and characterised by a relatively low density, separate from the rest of the material. The difference in concentration of magnesium in the calcite particles causes various degrees of hardness, density, and pressure in different regions of the material. Magnesium-rich particles compress the inner part of the lens as it crystallizes and “temper” it into a clear and tough crystalline material.

Boaz Pokroy, professor at the Technion and leading scientist, explains: “Nature exhibits tremendous creativity in improving the organism’s abilities in various contexts such as strength, sensing, and self-defense. Here, too, in the process of creating hardy and precise transparent lenses, we see tremendous efficiency in the use of existing raw materials under conditions in the natural environment”. Brittle starts could hence open the door to new engineering processes for tempered glass, optical lenses or even biomaterial implants.

An alga’s special resistant shape

The effect of magnesium also had a big impact in another marine organism: the alga Jania sp. Research done by Pokroy and his team on ID16B, ID19 and ID22, showed that the alga has a structure of 64% porosity and it develops a helix shape that makes it 20% more compliant to resist the bending forces the sea currents inflict on it.

“These findings are of great importance in deepening the understanding of nature’s designs, and it is potentially relevant for the development of new low-weight, high-compliance structures”, adds Pokroy. One example that could benefit from this research is concrete. This material is very brittle and does not stand bending forces, and so today manufacturers add steel into it. If it could adopt a helical open-cells structure, it could bring down the weight and make it more flexible and resistant.

References:

 Nuphar Bianco-Stein, et al. PNAS, 119(16) e2120177119, https://doi.org/10.1073/pnas.2120177119

Polischuk, I. et al, ​Science  08 Dec 2017: Vol. 358, Issue 6368, pp. 1294-1298. DOI: 10.1126/science.aaj2156

Bianco-Stein N, et al, Advanced Science, 21 April 2020. https://doi.org/10.1002/advs.202000108

Text by Montserrat Capellas Espuny. Video by Mark McGee and Montserrat Capellas Espuny.