Scientists discover how sea cucumbers change shape


Sea cucumbers can rapidly change the stiffness of their body, and scientists from Queen Mary University of London (QMUL) have discovered for the first time how they do it using data collected at ESRF. The research can provide a useful basis for developing novel biomaterials for applications in medicine.

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One of the most abundant molecules in the human body is collagen, a structural protein that forms our bones, ligaments and skin.  Once these tissues are formed, their mechanical properties can only be changed slowly over days or weeks.

All animals have collagen, but one group of marine invertebrates – the echinoderms, which includes starfish and sea cucumbers – have evolved to have collagenous tissues with a unique property: they can rapidly change their stiffness. This type of collagen is known as mutable collagenous tissue (MCT) and is controlled by the nervous system. It is useful when, for example the animals need to ‘turn to jelly’ so they can avoid predation.  However, the mechanisms by which the sea cucumber can change its stiffness were not known until now.

Lead author Himadri Gupta from QMUL's Institute of Bioengineering, said: “The sea cucumber's MCT may serve as a template for bio-inspired materials, which can mimic its remarkable properties. These could be useful in flexible scaffolds for tissue engineering, cosmetic treatments against skin ageing, implantable biosensors, and materials for soft robotics.”

Reporting in the journal Proceedings of the National Academy of Sciences, the QMUL team analysed the body wall of sea cucumbers at the ESRF.  The team used the technique of time-resolved synchrotron small-angle X-ray diffraction combined with in situ tensile testing carried out at the high-brilliance beamline ID02. Sylvain Prevost, scientist at the ESRF and co-author of the study explains that “this experiment required a high flux, a small beam (20 µm) at the sample matching domains size in the tissue, a very low background and a detector with high sensitivity and resolution, which we got thanks to the FReLoN camera developed inhouse”.


In situ nanomechanics with synchrotron SAXD. Experimental configuration: Tensile tester (Center) with MCT specimen mounted along the X-ray beam path in transmission geometry with CCD detector (Left). (Right, Inset) Magnified view of sample in chamber and incident X-ray beam (right) with SAXD scattering shown on left. The tensile strain is applied along the vertical direction. Credits: PNAS.

The sea cucumber's ability to change the shape of the body wall is due to the changes in the stiffness of a protein-rich interfibrillar matrix, which bonds with the collagen fibrils. Co-author Maurice Elphick from QMUL's School of Biological and Chemical Sciences, said: “Sea cucumbers are amazingly flexible and this study shows that their ability to shape-shift is not a result of any changes within the collagen fibrils themselves, but in the interfibrillar scaffold that cross-links with them.”    

The researchers hope to narrow down and isolate the molecules that lead to these properties of the sea cucumber's body wall, which in turn, can help in understanding how to apply this research in medicine and cosmetics.

Mo, J. et al, PNAS, October 5, 2016. DOI:10.1073/pnas.1609341113




Top image: A sea cucumber. Credits: Maxim Gavrilyuk.