Morphometric structural diversity of a natural armor assembly investigated by 2D continuum strain analysis
Journal of Structural Biology
Many armored fish scale assemblies use geometric heterogeneity of subunits as a design parameter to provide tailored biomechanical flexibility while maintaining protection from external penetrative threats. This study analyzes the spatially varying shape of individual ganoid scales as a structural element in a biological system, the exoskeleton of the armored fish P. senegalus (bichir). X-ray microcomputed tomography is used to generate digital 3D reconstructions of the mineralized scales.
... ark-based geometric morphometrics is used to measure the geometric variation among scales and to define a set of geometric parameters to describe shape variation. A formalism using continuum mechanical strain analysis is developed to quantify the spatial geometry change of the scales and illustrate the mechanisms of shape morphing between scales. Five scale geometry variants are defined (average, anterior, tail, ventral, and pectoral fin) and their functional implications are discussed in terms of the interscale mobility mechanisms that enable flexibility within the exoskeleton. The results suggest that shape variation in materials design, inspired by structural biological materials, can allow for tunable behavior in flexible composites made of segmented scale assemblies to achieve enhanced user mobility, custom fit, and flexibility around joints for a variety of protective applications. different given geometries are from each other. Geometric heterogeneity in scale shape divides the P. senegalus exoskeleton into five variants (average, anterior, tail, ventral, and pectoral fin) which utilize different shape-based joint articulation mechanism to move relative to each other within the integument. The technique can also be used to morph a shape into a target geometry with the application of a heterogeneous strain field. In the future, this technique may be used to analyze the geometry change and concomitant changes in interscale mobility mechanisms during the fish's growth and development, for instance comparing the juvenile elasmoid scales of P. senegalus to the adult ganoid scales (Sire, 1989) . The results can be used to develop computational shape morphing algorithms such as our MetaMesh model (Duro-Royo et al., 2014), which defines local, regional, and global hierarchies of design rules of an articulated assembly of P. senegalus-inspired sub-units that adapts to complex hosting surfaces. We postulate that shape and shape variation can be used as materials design parameters to tailor the mechanical behavior of materials. Our concurrent work fabricates flexible composite prototypes based on the P. senegalus exoskeleton and experimentally characterizes their mechanical behavior. Our future work also seeks to integrate both material heterogeneity, as explored by Araya et al. (2013) , and geometric heterogeneity into armor materials that are tailorable to the needs of a wide variety of protective applications, such as custom fit, user mobility, and flexibility around joints. Conflict of interest statement The authors have no financial and personal relationships with other people or organizations that could influence their work. 4 5 6 7 8