When a crustacean exoskeleton becomes a remarkable biological harpoon
The findings of a multidisciplinary study involving three laboratories of the University of Liège used multiple material science characterization methods to investigate the spike of the mantis shrimp, a biological harpoon based on chitin. They revealed several morphological, compositional, microstructural and biomechanical features allowing this harpoon to combine high stiffness and toughness with low weight. These results have been published in the top-tier journal “Natural Sciences” and featured on the front cover.
Nature is an endless source of inspiration for developing new engineering materials. Spearing mantis shrimps are aggressive crustaceans using specialized appendages with sharp spikes to capture fish. These legs are deployed incredibly fast, and the spikes have to combine high toughness, as required by the initial impact with the prey, with high stiffness and strength to ensure sufficient penetration while avoiding breaking. Yann Delaunois, co-supervised by Philippe Compère from the functional and evolutionary morphology lab (Faculty of Sciences) and Davide Ruffoni from the MBBM lab (School of Engineering / AM), performed a multimodal analysis to uncover the design strategies of these biological harpoons. The work was performed in collaboration with Alexandra Tits and Quentin Grossman from the MBBM lab, Sarah Smeets from the FOCUS research unit, Cédric Malherbe and Gauthier Eppe from the MolSys Research Unit (Faculty of Sciences) and Harry van Lenthe from KU Leuven.
“The central aim of the project was to elucidate the structure-function relationship and the mechanical behaviour of the spike,” explains Yann Delaunois, leader of the project. To do this, the expertise of several laboratories was exploited to combine many techniques, including micro-computed tomography, electron microscopy, spectroscopy, depth sensing nanoindentation and multi-material 3D printing. “We found that each spike of the shrimp is a slightly hooked hollow beam with the outer surface decorated by serrations and grooves to enhance cutting and interlocking. The material constituting the spikes is an exoskeleton that is a multilayer composite, with each region having specific morphological and mechanical features,” continues Yann. The study's central finding is the presence of a tiny interphase integrating the outer and inner regions having very different behaviours. Such a small region has the remarkable ability to hamper crack propagation. “To further highlight the mechanical role of this interphase, we used 3D multi-material printing, mimicking the observed construction principles into synthetic materials”, explains Yann. Those tests revealed that spike-inspired composites could provide superior damage resistance.
“In the light of the endless advancement in nano- and microscale manufacturing methods, the biological tool investigated here could inspire the design of new man-made composites, for example, based on environmentally friendly and recyclable building units as seen in the spike cuticle, with improved wear resistance and puncture abilities for repeated piercing on different surfaces”, concludes Davide Ruffoni, head of the MBBM lab and co-supervisor of the project.
Scientific reference
Yann Delaunois, Alexandra Tits, Quentin Grossman, Sarah Smeets, Cedric Malherbe, Gauthier Eppe, Harry van Lenthe, Davide Ruffoni, and Philippe Compere, Design Strategies of the Mantis Shrimp Spike: How the Crustacean Cuticle Became a Remarkable Biological Harpoon?, Natural Sciences, 9 March 2023.
Article is available in open access : https://doi.org/10.1002/ntls.20220060
