Mantis shrimp's 'armed' power

Feng Zengkun The Straits Times AsiaOne 24 Apr 14;

SINGAPORE - The future of medical devices such as hip implants and prosthetic limbs, and even body armour, could literally lie in the arms of a tiny sea creature.

Researchers in Singapore have found out why the tiny mantis shrimp is able to strike its prey at the speed of a 5.56mm rifle bullet while suffering little to no damage to its club-like arms.

The team identified not only the arm's components but also how its inner arrangement improves its ability to absorb forces without harm. This work could lead to incredibly damage-resistant products for people.

The team, led by Assistant Professor Ali Miserez and graduate student Shahrouz Amini from Nanyang Technological University (NTU), published its findings in the prestigious scientific journal Nature Communications in January.

The findings put researchers globally one step closer to replicating the material. But the team - from NTU's School of Materials Science and Engineering and School of Biological Sciences and elsewhere - said this would likely take at least three to four years.

While the components are easy to find and reproduce, said Prof Miserez, "the challenge is to reproduce the structure with the same level of organisation that you would find in the natural system".

The mantis shrimp arm's key element is a mineral called fluorapatite.

This is also found in shark's teeth. More importantly, it is very similar to the hydroxyapatite in human teeth and bone.

"You would need to have the proper tests and controls, but there is no reason why it wouldn't be biocompatible with people," said Prof Miserez. "It's almost the exact same thing we already have in our bodies."

Biocompatible implants would address bone loss from wear and tear, as well as toxic and immunity reactions from fine particles in metal implants.

The shrimp's arm also contains calcium sulphate, a common chemical used in plaster of Paris, and calcium carbonate, which exists naturally as chalk and limestone and also helps form mollusc shells and stony corals.

The sulphate helps the fluorapatite become more crystalline in the arm's outer layers, adding to its hardness. The fluorapatite in the inner layers, on the other hand, exists in a softer glassy form, which helps the arm absorb forces like a cushion.

"With these findings we can take calcium sulphate - which is easy enough to buy - and use it to try and crystallise fluorapatite to create strong and biocompatible materials," said Prof Miserez.

The scientists plan to further study the arm's structure, chemistry and mechanics, and how the shrimp is able to strike so quickly. They will also use computer simulations to examine exactly what happens to the arm when it hits an object.
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