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Matrix-induced pre-strain and mineralization-dependent interfibrillar shear transfer enable 3D fibrillar deformation in a biogenic armour

DOI: 10.1016/j.actbio.2019.09.036 DOI Help

Authors: Yanhong Wang (Queen Mary University of London) , Yi Zhang (Institute of High Energy Physics, Chinese Academy of Science) , Nicholas J. Terrill (Diamond Light Source) , Ettore Barbieri (Japan Agency for Marine-Earth Science and Technology (JAMSTEC)) , Nicola M. Pugno (University of Trento; Queen Mary University of London; Via del Politecnico snc) , Himadri Gupta (Queen Mary University of London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Biomaterialia

State: Published (Approved)
Published: September 2019
Diamond Proposal Number(s): 17869

Abstract: The cuticle of stomatopod is an example of a natural mineralized biomaterial, consisting of chitin, amorphous calcium carbonate and protein components with a multiscale hierarchical structure, and forms a protective shell with high impact resistance. At the ultrastructural level, cuticle mechanical functionality is enabled by the nanoscale architecture, wherein chitin fibrils are in intimate association with enveloping mineral and proteins. However, the interactions between these ultrastructural building blocks, and their coupled response to applied load, remain unclear. Here, we elucidate these interactions via synchrotron microbeam wide-angle X-ray diffraction combined with in situ tensile loading, to quantify the chitin crystallite structure of native cuticle – and after demineralization and deproteinization – as well as time-resolved changes in chitin fibril strain on macroscopic loading. We demonstrate chitin crystallite stabilization by mineral, seen via a compressive pre-strain of approximately 0.10% (chitin/protein fibre pre-stress of ∼20 MPa), which is lost on demineralization. Clear reductions of stiffness at the fibrillar-level following matrix digestion are linked to the change in the protein/matrix mechanical properties. Furthermore, both demineralization and deproteinization alter the 3D-pattern of deformation of the fibrillar network, with a non-symmetrical angular fibril strain induced by the chemical modifications, associated with loss of the load-transferring interfibrillar matrix. Our results demonstrate and quantify the critical role of interactions at the nanoscale (between chitin-protein and chitin-mineral) in enabling the molecular conformation and outstanding mechanical properties of cuticle, which will inform future design of hierarchical bioinspired composites.

Journal Keywords: Chitin-based biomaterials; Nanoscale mechanics; in situ synchrotron wide-angle; X-ray diffraction; Fibrillar deformation; Arthropod cuticle

Subject Areas: Biology and Bio-materials

Instruments: I22-Small angle scattering & Diffraction