Macro-to-nano scale investigation of wall-plate joints in the acorn barnacle Semibalanus balanoides: correlative imaging, biological form and function, and bioinspiration

Abstract

1.AbstractCorrelative imaging combines information from multiple modalities (physical-chemical-mechanical properties) at various length-scales (cm to nm) to understand complex biological materials across dimensions (2D-3D). Here, we have used numerous coupled systems: X-ray microscopy (XRM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), optical light microscopy (LM), and focused-ion beam (FIB-SEM) microscopy to ascertain the microstructural and crystallographic properties of the wall-plate joints in the barnacle Semibalanus balanoides. The exoskeleton is composed of six interlocking wall-plates, and the interlocks between neighbouring plates (alae) allow barnacles to expand and grow whilst remaining sealed and structurally strong. Our results indicate that the ala contain functionally-graded orientations and microstructures in their crystallography, which has implications for naturally functioning microstructures, potential natural strengthening, and preferred oriented biomineralisation. Elongated grains at the outer edge of the ala are oriented perpendicularly to the contact surface, and the c-axis rotates with the radius of the ala. Additionally, we identify for the first time three-dimensional nano-scale ala pore networks revealing that the pores are only visible at the tip of the ala, and that pore thickening occurs on the inside (soft-bodied) edge of the plates. The pore networks appear to have the same orientation as the oriented crystallography, and we deduce that the pore networks are probably organic channels and pockets which are involved with the biomineralisation process. Understanding these multi-scale features contributes towards an understanding of the structural architecture in barnacles, but also their consideration for bioinspiration of human-made materials. The work demonstrates that correlative methods spanning different length-scales, dimensions and modes enable the extension of structure-property relationships in materials to form and function of organisms.

Microstructure and crystallography of the wall plates of the giant barnacleAustromegabalanus psittacus: a material organized by crystal growth

“…In their EBSD study on the alae of Semibalanus balanoides, Mitchell et al [10] revealed areas of even orientations, which, in the absence of an SEM study, they interpreted as individual grains. Given their sizes, they are rather CCRs of the type recognized here.…”

“…At the base plate, the calcite crystals' c-axes are perpendicular to the base plate close to the substrate and later change to become parallel to the attachment surface towards the middle of the base plate. EBSD maps obtained on the margins of the alae in the horizontal section revealed crystalline domains with complex boundaries, which elongated perpendicular to the growth margin, thus having a radial arrangement [10]. The c-axes of these domains display a similar distribution.…”

Macro-to-nanoscale investigation of wall-plate joints in the acorn barnacle Semibalanus balanoides : correlative imaging, biological form and function, and bioinspiration

“…Additional files supporting this article have been uploaded as part of the electronic supplementary material, S1–S4. XRM scans (tiff stacks) of whole barnacles mounted in resin and individual plates are available from the Dryad Digital Repository at: [74].…”

“…However, little is understood about how macro-micro-nanoscale structures, particularly in the shell, are linked. Correlative imaging provides an opportunity to discover the multiscale interactions and mechanisms involved in the structure of complex systems at varying length scales [26][27][28][29] and, specifically for barnacles, provides an opportunity to correlate optical, analytical, structural and mechanical information [30] for the first time. Here, we have coupled numerous systems at various length scales: X-ray microscopy (XRM), scanning electron microscopy (SEM), light microscopy (LM) and focussed ion beam microscopy (FIB-SEM) to ascertain the macro-to-nanoscale structure, crystallographic orientation and mechanical properties of wall-plate joints in the parietal exoskeleton of the barnacle Semibalanus balanoides.…”