Tag Archives: sea urchins

Heart urchin shells and air

This is a microscale (1 millionth) rather than a nanoscale (1 billionth) story but I find the idea of shells that are mostly composed of air quite intriguing. From a Nov. 10, 2015 news item on ScienceDaily,

Materials researchers love sea creatures. Mother-of-pearl provokes ideas for smooth surfaces, clams inspire gluey substances, shark’s skin is used to develop materials that reduce drag in water, and so on. Researchers have now found a model for strong, lightweight materials by diving below the sea surface to investigate a sea urchin cousin known as the heart urchin.

A Nov. 9, 2015 University of Copenhagen press release (also on EurekAlert), which originated the news item, provides more details,

Heart urchins (Echinocardium cordatum), also known as sea potatoes, measure up to 5 cm in diameter, are heart shaped and burrow in sand. They extend a channel to feed upon organic particles from the waters above their burrow. Like “regular” sea urchins, these “irregular” heart urchins are soft creatures that use their calcium carbonate exoskeletons to protect their otherwise edible bodies from predation. And as it turns out, their shells are unexpectedly robust.

The idea to study heart urchin shells dawned upon a vacationing Müter while he was walking down a Croatian beach. The paper-thin urchin shells were washed up onto the beach, and Müter [Dirk Müter, assistant professor in the Department of Chemistry’s NanoGeoScience research group] observed that they had astonishingly few blemishes despite being so thin.

To understand the sturdy calcium carbonate shells, Müter and his colleagues used a relatively new technology called x-ray microtomography. The technique was used to create three-dimensional images of the material contents, without having to break the shells up into pieces. The x-ray images are so fine that it is possible to distinguish structures of less than one-thousandth of a millimetre. This ultra fine resolution proved decisive in coming to understand the shell’s strength.

Anyone who has ever broken a piece of chalk knows that calcium carbonate is fragile. And, heart urchin shells consist of more air than chalk. In fact, as one gets up close to the shell material, it begins to resemble soapsuds. The material consists of an incredible number of microscopic cavities held together by slender calcium carbonate (chalk) struts. There are between 50,000 and 150,000 struts per cubic millimetre, and in some areas, the material is composed of up to 70% air.

Calcium carbonate can be many things, from unyielding marble to the soft and somewhat brittle chalk that we use to write with. While heart urchin shells and writing chalk share a similar porosity, the urchin shells are up to six times stronger than chalk. Müter’s studies demonstrate that heart urchin shells have a structure that nears a theoretical ideal for foam structure strength – a must for a creature that has evolved to withstand life under 10 metres of water and an additional 30 centimetres of sand.

Müter explains that to their great surprise, heart urchin shell strength varied between shell regions due to greater or lesser concentrations of struts within specific regions, not because of thinner or thicker struts.

“We found an example of a surprisingly simple construction principle. This is an easy way to build materials. It allows for great variation in structure and strength. And, it is very near optimal from a mechanical perspective,” states Assistant Professor Dirk Müter.

Müter and his NanoGeoScience colleagues expect that their new insights will serve to improve shock- absorbent materials among other outcomes.

Here is Müter holding up a sea potato or sea heart,

Caption: The heart urchin lives its entire life dug into the sea bottom. Its fragile looking calcium shell needs to withstand the combined pressure of half a meter of sand and a couple of meters water. Dirk Müter of University of copenhagen Department of Chemistry, discovered, that this makes it one of the toughest creatures known. Credit Photo: Jes Andersen/University of Copenhagen

Caption: The heart urchin lives its entire life dug into the sea bottom. Its fragile looking calcium shell needs to withstand the combined pressure of half a meter of sand and a couple of meters water. Dirk Müter of University of copenhagen Department of Chemistry, discovered, that this makes it one of the toughest creatures known. Credit Photo: Jes Andersen/University of Copenhagen

Here’s a link to and a citation for the paper,

Microstructure and micromechanics of the heart urchin test from X-ray tomography by D. Müter, , H.O. Sørensen, J. Oddershede, K.N. Dalby, and S.L.S. Stipp. Acta Biomaterialia Volume 23, 1 September 2015, Pages 21–26 doi:10.1016/j.actbio.2015.05.007

This paper is behind a paywall.

Sea urchins taste yummy and (might) hold key to carbon capture

A prized sushi food item, sea urchins use nickel particles to convert carbon dioxide according to a Feb. 5, 2013 news item on ScienceDaily,

The discovery that sea urchins use nickel particles to harness carbon dioxide from the sea could be the key to capturing tons of carbon dioxide (CO2) from the atmosphere.

Experts at Newcastle University, UK, have discovered that in the presence of a nickel catalyst, CO2 can be converted rapidly and cheaply into the harmless, solid mineral, calcium carbonate.

This discovery, which is published February 5 in the academic journal Catalysis Science & Technology, has the potential to revolutionize the way we capture and store carbon enabling us to significantly reduce CO2 emissions — the key greenhouse gas responsible for climate change.

The Newcastle University Feb. 5, 2013 news release, which originated the news item, details how this discovery came about,

Dr Lidija Šiller, a physicist and Reader in Nanoscale Technology at Newcastle University, says the discovery was made completely by chance.

“We had set out to understand in detail the carbonic acid reaction – which is what happens when CO2 reacts with water – and needed a catalyst to speed up the process,” she explains.

“At the same time, I was looking at how organisms absorb CO2 into their skeletons and in particular the sea urchin which converts the CO2 to calcium carbonate.

“When we analysed the surface of the urchin larvae we found a high concentration of Nickel on their exoskeleton.  Taking Nickel nanoparticles which have a large surface area, we added them to our carbonic acid test and the result was the complete removal of CO2.”

Before discussing the implications it’s useful to understand the current situation regarding carbon capture processes, from the news release,

At the moment, pilot studies for Carbon Capture and Storage (CCS) systems propose the removal of CO2 by pumping it into holes deep underground.  However, this is a costly and difficult process and carries with it a long term risk of the gas leaking back out – possibly many miles away from the original downward source.

An alternative solution is to convert the CO2 into calcium or magnesium carbonate.

“One way to do this is to use an enzyme called carbonic anhydrase,” explains Gaurav Bhaduri, lead author on the paper and a PhD student in the University’s School of Chemical Engineering and Advanced Materials.

“However, the enzyme is inactive in acid conditions and since one of the products of the reaction is carbonic acid, this means the enzyme is only effective for a very short time and also makes the process very expensive.

“The beauty of a Nickel catalyst is that it carries on working regardless of the pH and because of its magnetic properties it can be re-captured and re-used time and time again. It’s also very cheap – 1,000 times cheaper than the enzyme.  And the by-product – the carbonate – is useful and not damaging to the environment.

“What our discovery offers is a real opportunity for industries such as power stations and chemical processing plants to capture all their waste CO2 before it ever reaches the atmosphere and store it as a safe, stable and useful product.”

Each year, humans emit on average 33.4 billion metric tons of CO2 – around 45% of which remains in the atmosphere.  Typically, a petrol-driven car will produce a ton of CO2 every 4,000 miles.

Calcium carbonate, or chalk, makes up around 4% of the Earth’s crust and acts as a carbon reservoir, estimated to be equivalent to 1.5 million billion metric tons of carbon dioxide.

It is the main component of shells of marine organisms, snails, pearls, and eggshells and is a completely stable mineral, widely used in the building industry to make cement and other materials and also in hospitals to make plaster casts.

The process developed by the Newcastle team involves passing the waste gas directly from the chimney top, through a water column rich in Nickel nano-particles and recovering the solid calcium carbonate from the bottom.

Dr Šiller adds: “The capture and removal of CO2 from our atmosphere is one of the most pressing dilemmas of our time.

“Our process would not work in every situation – it couldn’t be fitted to the back of a car, for example – but it is an effective, cheap solution that could be available world-wide to some of our most polluting industries and have a significant impact on the reduction of atmospheric CO2.”

According the news release the researchers have patented the process and are looking for investors as they plan for future development.