Modeling Bioinspired Fish Scale Designs via a Geometric and Numerical Approach.

Fish scales serve as a natural dermal armor with remarkable flexibility and puncture resistance. Through studying fish scales, researchers can replicate these properties and tune them by adjusting their design parameters to create biomimetic scales. Overlapping scales, as seen in elasmoid scales, can lead to complex interactions between each scale. These interactions are able to maintain the stiffness of the fish's structure with improved flexibility. Hence, it is important to understand these interactions in order to design biomimetic fish scales. Modeling the flexibility of fish scales, when subject to shear loading across a substrate, requires accounting for nonlinear relations. Current studies focus on characterizing these kinematic linear and nonlinear regions but fall short in modeling the kinematic phase shift. Here, we propose an approach that will predict when the linear-to-nonlinear transition will occur, allowing for more control of the overall behavior of the fish scale structure. Using a geometric analysis of the interacting scales, we can model the flexibility at the transition point where the scales start to engage in a nonlinear manner. The validity of these geometric predictions is investigated through finite element analysis. This investigation will allow for efficient optimization of scale-like designs and can be applied to various applications.

Micromorphology of osteoderms in Dasypodidae (Cingulata, Mammalia): Characterization and 3D-reconstructions.

Osteoderms are present in a variety of extinct and extant vertebrates, but among mammals, the presence of osteoderms is essentially restricted to armadillos (Cingulata, Dasypodidae). Osteoderms have been proposed to exhibit a variety of functionalities in Dasypodidae, mainly protection and thermoregulation, and they have been considered as one of the synapomorphies of this group. In this study, we use high-resolution microcomputed tomography to describe the osteoderm micromorphology of several extant species of Dasypodidae in a comparative context. This study allowed the identification, 3D-reconstruction and volume quantification of different internal structures of osteoderms as well as their interrelations. This detailed characterization of the internal osteoderm morphology was compared in a phylogenetic context to assess the evolutionary trends of the species involved. This enables the identification of distinctive patterns for the most widely recognized clades, the Dasypodinae and Euphractinae with a morphological homogeneity in the microstructure of their osteoderms, in comparison with Tolypeutinae where it has not been possible to establish a common morphological pattern. The most important features for linage differentiation is the degree of compaction of the osteoderms, the number of cavities and the development of hairs. It is likely that the differential development of the various structures occurred as adaptive response to climate changes.

A comparative study of bio-inspired protective scales using 3D printing and mechanical testing.

Flexible natural armors from fish, alligators or armadillo are attracting an increasing amount of attention for their unique combinations of hardness, flexibility and light weight. The extreme contrast of stiffness between hard scales and surrounding soft tissues gives rise to unusual and attractive mechanisms, which now serve as models for the design of bio-inspired armors. Despite this growing interest, there is little guideline for the choice of materials, optimum thickness, size, shape and arrangement for the protective scales. In this work, we explore how the geometry and arrangement of hard scales can be tailored to promote scale-scale interactions. We use 3D printing to fabricate arrays of scales with increasingly complex geometries and arrangements, from simple squares with no overlap to complex ganoid-scales with overlaps and interlocking features. We performed puncture tests and flexural tests on each of the 3D printed materials, and we report the puncture resistance - compliance characteristics of each design on an Ashby chart. The interactions between the scales can significantly increase the resistance to puncture, and these interactions can be maximized by tuning the geometry and arrangement of the scales. Interestingly, the designs that offer the best combinations of puncture resistance and flexural compliance are similar to the geometry and arrangement of natural teleost and ganoid scales, which suggests that natural evolution has shaped these systems to maximize flexible protection. This study yields new insights into the mechanisms of natural dermal armor, and also suggests new designs for personal protective systems. STATEMENT OF SIGNIFICANCE: Flexible natural armors from fishes, alligators or armadillos are attracting an increasing amount of attention for their unique and attractive combinations of hardness, flexibility and low weight. Despite a growing interest in bio-inspired flexible protection, there is still little guideline for the choice of materials, optimum thickness, size, shape and arrangement of the protective scales. In this work, we explore how the geometry and arrangement of hard scales affect puncture resistance and flexural compliance, using 3D printing and mechanical testing. Our main finding is that the performance of the scaled skin in terms of puncture resistance can be significantly improved by slight changes in their geometry and arrangement. Our results also suggest that natural evolution has shaped scaled skins to maximize flexible protection. This study yields new insights into the mechanics of natural dermal armors, and also suggests new designs for personal protective systems.

3D-printing and mechanics of bio-inspired articulated and multi-material structures.

3D-printing technologies allow researchers to build simplified physical models of complex biological systems to more easily investigate their mechanics. In recent years, a number of 3D-printed structures inspired by the dermal armors of various fishes have been developed to study their multiple mechanical functionalities, including flexible protection, improved hydrodynamics, body support, or tail prehensility. Natural fish armors are generally classified according to their shape, material and structural properties as elasmoid scales, ganoid scales, placoid scales, carapace scutes, or bony plates. Each type of dermal armor forms distinct articulation patterns that facilitate different functional advantages. In this paper, we highlight recent studies that developed 3D-printed structures not only to inform the design and application of some articulated and multi-material structures, but also to explain the mechanics of the natural biological systems they mimic.

Osteoderm histology of Proterochampsia and Doswelliidae (Reptilia: Archosauriformes) and their evolutionary and paleobiological implications.

Postcranial osteoderms are commonly developed in the major lineages of Archosauriformes, including forms such as proterochampsids and doswelliids. Here, we survey the histology of osteoderms of the doswelliids Archeopelta arborensis and Tarjadia ruthae, and the proterochampsids Chanaresuchus bonapartei and Pseudochampsa ischigualastensis to understand better the morphogenesis of these skeletal elements. Whereas, the Doswelliid osteoderms possess a trilaminar organization, in which two cortices (external and basal) can be differentiated from an internal core of cancellous bone, these elements are compact structures in proterochampsids. The osteoderms of P. ischigualastensis are avascular and they consist entirely of parallel-fibered bone. Conversely, the osteoderms of C. bonapartei are well vascularized structures composed of zones of woven-fibered bone and annuli of parallel-fibered bone. The rather simple microstructure observed in P. ischigualastensis osteoderms suggests that these elements grew at a constant, low rate. Compared with proterochampsids, doswelliid osteoderms possess a more complex histology, which appears to be linked to variations in the growth rate during the osteoderm formation and also to the development of the external ornamentation. A comparison of our findings with the results of earlier studies on other archosauriforms (phytosaurs and pseudosuchians) reveals that the general osteoderm histology of doswelliids bears a closer resemblance to that of phytosaurs and pseudosuchians than the proterochampsid osteoderm microstructure. If all archosauriform osteoderms are homologous structures, the closer resemblance of doswellid osteoderm microstructures to that of phytosaurs and pseudosuchians is in agreement with the hypothesis that doswellids are more closely related to archosaurs than proterochampsids. J. Morphol. 276:385-402, 2015. © 2015 Wiley Periodicals, Inc.

Bone histology of phytosaur, aetosaur, and other archosauriform osteoderms (Eureptilia, Archosauromorpha).

As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well-developed osteoderms. Here we provide a comparative study on the microstructure of phytosaur (five taxa) and aetosaur (thirteen taxa) osteoderms. For outgroup comparison, we sampled osteoderms of the sister taxon to Aetosauria, Revueltosaurus callenderi, and the doswelliid Jaxtasuchus salomoni. Phytosaur, aetosaur, and Jaxtasuchus osteoderms are composed of a diploe structure, whereas the Revueltosaurus osteoderm microanatomy is more compact. The external cortex of phytosaurs, Revueltosaurus and Jaxtasuchus osteoderms is mainly composed of parallel-fibered bone. In aetosaurs, the external cortex mainly consists of lamellar bone, with lines of resorption within the primary bone indicating successive cycles of bone erosion and deposition. The basal cortex in all the specimens is composed of parallel-fibered bone, with the cancellous internal core being more strongly developed in aetosaurs than in phytosaurs. Woven or fibro-lamellar bone was recorded in both phytosaurian and aetosaurian taxa, as well as in Jaxtasuchus. Structural fibers, which at least partly suggest metaplastic origin, were only recorded in the internal core of two phytosaurs and in the basal cortex of one aetosaur. Osteoderm thickness and cancellous to compact bone ratios appear to be subject to ontogenetic change. Minimum growth mark counts in osteoderms sampled indicate that some aetosaurs and phytosaurs lived for at least two decades. Bone microstructures are more uniform in phytosaur osteoderms and show a higher level of disparity among aetosaur osteoderms, and at least in the latter, histological features are potentially apomorphic for species/genus level.