The most powerful punch in the natural world

28 June 2022
Thorbjørn Erik Køppen Christensen studies how the properties of the stomatopod’s dactyl club surpass those of the components it is made of. That knowledge could be useful when developing stronger and more durable objects in the future.

The stomatopod, which is also nicknamed the mantis shrimp due to its shrimp-like appearance, is typically found around the equator and it varies between 10 and 38 centimetres in size. However, according to SDC PhD student Thorbjørn Erik Køppen Chrisensen, the truly impressive feature of the creature is its impressive weapon of choice.

The stomatopod is amazing. It hunts and kills crabs and mussels punching their shells with the force of a .22 calibre rifle using its two dactyl clubs. The shells of its prey break, but the clubs do not, even though they are made of roughly the same material. Therefore, it is interesting to understand not only the structure of the clubs, but also the chemistry that produces them. Maybe, in the future, we can imitate those structures and make stronger objects or buildings,’ says Thorbjørn Erik Køppen Chrisensen.

Thorbjørn began researching the stomatopod when he was still a master’s degree student at Aarhus University’s Interdisciplinary Nanoscience Center, iNANO. He was looking for an interesting thesis project and got the opportunity to research stomatopods with Professor Henrik Birkedal as his master’s thesis supervisor. After graduating, he received funding and was able to continue his work under Henrik Birkedal’s supervision as an SDC PhD.

Chasing Europe’s synchrotrons
The original idea for Thorbjørn was to carry out his experiments on the stomatopods using Chinese synchrotrons, but the coronavirus put a spanner in the works and instead he has carried out experiments on synchrotrons in France, Germany, and Sweden.

The synchrotron is a machine approximately the size of a football field that accelerates electrons to almost the speed of light producing an extremely brilliant light that is used for research. There are approximately 70 synchrotrons worldwide each costing billions of DKK to build. Therefore, when researchers want to use them for experiments, they must apply for a time slot.

Thorbjørn has primarily used DESY (Deutsches Elektronen-Synchrotron) in Hamborg, Germany and the shared European system ESRF (European Synchrotron Radiation Facility) in Grenoble, France. The ESRF can produce a light beam that is 50 nanometres wide, which means that he can scan for very small details.

When my research group is assigned a synchrotron time slot, we typically go there for a week and we more or less work 24/7, because time is precious, and we have to make the most of it. Once we are done, we have enough data to sort and analyse to keep us occupied for months,’ says Thorbjørn.
Once Thorbjørn is back from a trip he usually has millions of diffraction patterns to process and analyse. He does this by writing code on the computer that enables him to extract the data he needs in bulk.

Promising results
Thorbjørn’s research has shown that the crystal orientation distribution in the impact surface of the club is more complex, and that the chemical composition of the crystallites differs greatly throughout the club. The research also shows that the distribution of amorphous phases in the club are controlled, and that there is some degree of overengineering in the dactyl club.

We are getting a lot of good results that we will hopefully soon be able to publish. Our results help understanding the design of these fascinating biological hammers, which may serve as inspiration for future development of advanced bioinspired composites,’ he says.

Thorbjørn expects to conclude his PhD by the end of 2022. In the meantime, he still has a couple of trips to Grenoble left, some data processing at his office at iNANO and a couple of scientific articles to finish, but things are looking promising. After completing his PhD, Thorbjørn hopes to find a postdoc position.