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

Elasmoid fish scales as a natural fibre composite: microscopic heterogeneities in structure, mineral distribution, and mechanical properties

The elasmoid scales in teleost fish serve as exemplary models for natural fibre composites with integrated flexibility and protection. Yet, limited research has been focused on the potential structural, chemical, and mechanical heterogeneity within individual scales. This study presents systematic characterizations of the elasmoid scales from black drum fish (Pogonias cromis) at different zones within individual scales as a natural fibre composite, focusing on the microscopic structural heterogeneities and corresponding mechanical effects. The focus field at the centre of the scales exhibits a classical tri-layered collagen-based composite design, consisting of the mineralized outermost limiting layer, external elasmodine layer in the middle, and the unmineralized internal elasmodine layer. In comparison, the rostral field at the anterior end of the scales exhibits a two-layered design: the mineralized outermost limiting layer exhibits radii sections on the outer surface, and the inner elasmodine layer consists of collagen fibre-based sublayers with alternating mineralization levels. Chemical and nanoindentation analysis suggests a close correlation between the mineralization levels and the local nanomechanical properties. Comparative finite element modelling shows that the rostral-field scales achieve increased flexibility under both concave and convex bending. Moreover, the evolving geometries of isolated Mandle's corpuscles in the internal elasmodine layer, transitioning from irregular shapes to faceted octahedrons, suggest the mechanisms of mineral growth and space-filling to thicken the mineralized layers in scales during growth, which enhances the bonding strength between the adjacent collagen fibre layers. This work offers new insights into the structural variations in individual elasmoid scales, providing strategies for bioinspired fibre composite designs with local-adapted functional requirements.

The Behaviour of Stratified Fabrics of Aramid Fibres under Stabbing Conditions

This paper presents research on several factors influencing the stabbing behaviour of stratified panels made of aramid fabric Twaron® SRM509 Teijin Aramid BV (Arnhem, The Netherlands). The inputs in the test campaign were the number of layers, the impact energy, and the sample size. Tests were performed on small samples (130 mm × 130 mm) on an Instron® CEAST 9350 drop-tower impact system (Norwood, MA, USA) and on larger samples (400 mm × 400 mm) using a test installation with the same values of the impact energy. Knife type S1 was used, with the geometry recommended in NIJ Standard 0115.00 Stab Resistance of Body Armor SEM, and macro photography investigations revealed the failure mechanisms of panel, layers and fibres. A very important conclusion of this study regarding the stabbing performance of fabric Twaron® SRM 509 in particular, but also in general for panels for body protection is that a research study could start on small size samples, with an accurately instrumented machine, in order to establish the influence of significant factors of stab resistance (energy level, number of layers in a panel, etc.), as these samples are less expensive and less time consuming, but the study should be continued to examine larger size samples. The obtained data are useful for the prototype.

Programming Anisotropic Functionality of 3D Microdenticles by Staggered-Overlapped and Multilayered Microarchitectures

Natural sharkskin features staggered-overlapped and multilayered architectures of riblet-textured anisotropic microdenticles, exhibiting drag reduction and providing a flexible yet strong armor. However, the artificial fabrication of three-dimensional (3D) sharkskin with these unique functionalities and mechanical integrity is a challenge using conventional techniques. In this study, it is reported on the facile microfabrication of multilayered 3D sharkskin through the magnetic actuation of polymeric composites and subsequent chemical shape fixation by casting thin polymeric films. The fabricated hydrophobic sharkskin, with geometric symmetry breaking, achieves anisotropic drag reduction in frontal and backward flow directions against the riblet-textured microdenticles. For mechanical integrity, hard-on-soft multilayered mechanical properties are realized by coating the polymeric sharkskin with thin layers of zinc oxide and platinum, which have higher hardness and recovery behaviors than the polymer. This multilayered hard-on-soft sharkskin exhibits friction anisotropy, mechanical robustness, and structural recovery. Furthermore, coating the MXene nanosheets provides the fabricated sharkskin with a low electrical resistance of ≈5.3 Ω, which leads to high Joule heating (≈229.9 °C at 2.75 V). The proposed magnetomechanical actuation-assisted microfabrication strategy is expected to facilitate the development of devices requiring multifunctional microtextures.

Fish scale inspired structures-a review of materials, manufacturing and models

Fish scale inspired materials and structures can provide advanced mechanical properties and functionalities. These materials, inspired by fish scales, take the form of either composite materials or multi-material discrete exoskeleton type structures. Over the last decade they have been under intense scrutiny for generating tailorable and tunable stiffness, penetration and fracture resistance, buckling prevention, nonlinear damping, hydrodynamic and camouflaging functions. Such programmable behavior emerges from leveraging their unique morphology and structure-property relationships. Several advanced tools for characterization, manufacturing, modeling and computation have been employed to understand and discover their behavior. With the rapid proliferation of additive manufacturing techniques and advances in modeling and computational methods, this field is seeing renewed efforts to realize even more ambitious designs. In this paper we present a review and recapitulation of the state-of-the art of fish scale inspired materials.

Microstructure, mechanical properties and elemental composition of the terrestrial isopod Armadillidium vulgare cuticle

The exoskeletons of crustaceans are essential for providing protection from predators and other environmental threats. Understanding the structure and mechanical behavior of their natural armor could inspire the design of lightweight and high toughness synthetic materials. Most published work has focused on marine crustacea rather than their terrestrial counterparts, which are exposed to a multitude of unique threats. The interest in the terrestrial isopod Armadillidium vulgare (A. vulgare) has grown but the interrelationship between the microstructure, chemical composition, and mechanical properties has not been thoroughly investigated. Thus, this study aims to elucidate missing details concerning this biological mineralized composite. Exoskeleton specimens were fixated to preserve the intrinsic protein structure. We utilize scanning electron microscopy for microstructure analysis, Raman spectroscopy for elemental analysis, and nanoindentation property mapping to achieve mechanical characterization. The naturally fractured A. vulgare exoskeleton cross-section reveals four subregions with the repeating helicoidal 'Bouligand' arrangement most prominent in the endocuticle. The hardness and reduced modulus distributions exhibit a through-thickness exponential gradient with decreasing magnitudes from the outermost to the innermost layers of the exoskeleton. The Raman spectra show a graded spatial distribution of key constituents such as calcium carbonate across the thickness, some of which are consistent with the mechanical property gradient. Potential microstructure, elemental composition, and mechanical property relationships are discussed to explain how the hierarchical structure of this nanolaminate armor protects this species.

Intraspecific competition: A missing link in dermal armour evolution?

Predation is widely regarded as an important selective force in the evolution and maintenance of dermal armour; yet, the basic premise that predation and armour are strongly linked to each other has proven to be difficult to assess. In this concept, I put forward the fighting-advantage hypothesis, the view that aggressive interactions with conspecifics, not predation, might have been a key selective pressure in the evolution of dermal armour. Considering intraspecific competition as a potential explanation could not only reveal previously overlooked aspects of the functional and evolutionary significance of dermal armour, but also advance the emerging field of biomimetics in which such knowledge forms the starting point of technological innovation.

Porous morphology and graded materials endow hedgehog spines with impact resistance and structural stability

Hedgehog spines with evolved unique structures are studied on account of their remarkable mechanical efficiency. However, because of limitations of existing knowledge, it remains unclear how spines work as a material with a balance of stiffness and toughness. By combining qualitative three-dimensional (3D) structural characterization, material composition analysis, biomechanical analysis, and parametric simulations, the relationship between microstructural characteristic and multifunctional features of hedgehog spines is revealed here. The result shows that the fibers transform from the outer cortex to the interior cellular structures by the "T" section composed of the "L" section and a deltoid. The outer cortex, however, shows an arrangement of a layered fibrous structure. An inward change in Young's moduli is observed. In addition, these spines are featured with a sandwich structure that combines an inner porous core with an outer dense cortex. This feature confirms that the hedgehog spines are a kind of biological functionally graded fiber-reinforced composite. Biomimetic models based on the spine are then built, and the corresponding mechanical performance is tested. The results confirm that the internal cellular structure of the spine effectively improve impact resistance. Furthermore, the transverse diaphragm can prevent ellipticity, which may delay buckling. The longitudinal stiffeners also contribute to promote buckling resistance. The design strategies of the spine proposed here provide inspirations for designing T-joint composites. It also exhibits potential applications in low-density, impact and buckling resistance artificial composites. STATEMENT OF SIGNIFICANCE: The spines of a hedgehog are its protective armor that combines strength and toughness. The animal can not only withstand longitudinal and radial forces that are 1 × 10⁶∼ 3 × 10⁶ times the gravity generated by its own weight, but it can also survive unscathed by elastic buckling while dropping to the ground at a speed of up to 15 m/s. Here, we first demonstrate that hedgehog spines are biological graded fiber-reinforced structural composites and reveal their superior impact and buckling resistance mechanism through simulation analysis. Our results broaden the understanding of the relationship among morphology, materials, and function of hedgehog spines. It is anticipated that the survival strategies of hedgehog revealed here could provide inspirations for the development of synthetic composites with impact resistance and structural stability.

Damage-tolerant material design motif derived from asymmetrical rotation

Motifs extracted from nature can lead to significant advances in materials design and have been used to tackle the apparent exclusivity between strength and damage tolerance of brittle materials. Here we present a segmental design motif found in arthropod exoskeleton, in which asymmetrical rotational degree of freedom is used in damage control in contrast to the conventional interfacial shear failure mechanism of existing design motifs. We realise this design motif in a compression-resisting lightweight brittle material, demonstrating a unique progressive failure behaviour that preserves material integrity with 60–80% of load-bearing capacity at >50% of compressive strain. This rotational degree of freedom further enables a periodic energy absorbance pattern during failure yielding 200% higher strength than the corresponding cellular structure and up to 97.9% reduction of post-damage residual stress compared with ductile materials. Fifty material combinations covering 27 types of materials analysed display potential progressive failure behaviour by this design motif, thereby establishing a broad spectrum of potential applications of the design motif for advanced materials design, energy storage/conversion and architectural structures.

A review of the osteoderms of lizards (Reptilia: Squamata)

Osteoderms are mineralised structures consisting mainly of calcium phosphate and collagen. They form directly within the skin, with or without physical contact with the skeleton. Osteoderms, in some form, may be primitive for tetrapods as a whole, and are found in representatives of most major living lineages including turtles, crocodilians, lizards, armadillos, and some frogs, as well as extinct taxa ranging from early tetrapods to dinosaurs. However, their distribution in time and space raises questions about their evolution and homology in individual groups. Among lizards and their relatives, osteoderms may be completely absent; present only on the head or dorsum; or present all over the body in one of several arrangements, including non-overlapping mineralised clusters, a continuous covering of overlapping plates, or as spicular mineralisations that thicken with age. This diversity makes lizards an excellent focal group in which to study osteoderm structure, function, development and evolution. In the past, the focus of researchers was primarily on the histological structure and/or the gross anatomy of individual osteoderms in a limited sample of taxa. Those studies demonstrated that lizard osteoderms are sometimes two-layered structures, with a vitreous, avascular layer just below the epidermis and a deeper internal layer with abundant collagen within the deep dermis. However, there is considerable variation on this model, in terms of the arrangement of collagen fibres, presence of extra tissues, and/or a cancellous bone core bordered by cortices. Moreover, there is a lack of consensus on the contribution, if any, of osteoblasts in osteoderm development, despite research describing patterns of resorption and replacement that would suggest both osteoclast and osteoblast involvement. Key to this is information on development, but our understanding of the genetic and skeletogenic processes involved in osteoderm development and patterning remains minimal. The most common proposition for the presence of osteoderms is that they provide a protective armour. However, the large morphological and distributional diversity in lizard osteoderms raises the possibility that they may have other roles such as biomechanical reinforcement in response to ecological or functional constraints. If lizard osteoderms are primarily for defence, whether against predators or conspecifics, then this 'bony armour' might be predicted to have different structural and/or mechanical properties compared to other hard tissues (generally intended for support and locomotion). The cellular and biomineralisation mechanisms by which osteoderms are formed could also be different from those of other hard tissues, as reflected in their material composition and nanostructure. Material properties, especially the combination of malleability and resistance to impact, are of interest to the biomimetics and bioinspired material communities in the development of protective clothing and body armour. Currently, the literature on osteoderms is patchy and is distributed across a wide range of journals. Herein we present a synthesis of current knowledge on lizard osteoderm evolution and distribution, micro- and macrostructure, development, and function, with a view to stimulating further work.

Bioinspired buckling of scaled skins

Natural flexural armors combine hard, discrete scales attached to soft tissues, providing unique combinations of surface hardness (for protection) and flexibility (for unimpeded motion). Scaled skins are now inspiring synthetic protective materials which offer attractive properties, but which still suffer from limited trade-offs between flexibility and protection. In particular, bending a scaled skin with the scales on the intrados side jams the scales and stiffen the system significantly, which is not desirable in systems like gloves where scales must cover the palm side. Nature appears to have solved this problem by creating scaled skins that can form wrinkles and folds, a very effective mechanism to accommodate large bending deformations and to maintain flexural compliance. This study is inspired from these observations: we explored how rigid scales on a soft membrane can buckle and fold in a controlled way. We examined the energetics of buckling and stability of different buckling modes using a combination of discrete element modeling and experiments. In particular, we demonstrate how scales can induce a stable mode II buckling, which is required for the formation of wrinkles and which could increase the overall flexural compliance and agility of bioinspired protective elements.

The multiscale architecture of tessellated cartilage and its relation to function

When describing the architecture and ultrastructure of animal skeletons, introductory biology, anatomy and histology textbooks typically focus on the few bone and cartilage types prevalent in humans. In reality, cartilage and bone are far more diverse in the animal kingdom, particularly within fishes (Chondrichthyes and Actinopterygii), where cartilage and bone types are characterized by features that are anomalous or even pathological in human skeletons. This review discusses the curious and complex architectures of shark and ray tessellated cartilage, highlighting similarities and differences with their mammalian skeletal tissue counterparts. By synthesizing older anatomical literature with recent high-resolution structural and materials characterization work, this review frames emerging pictures of form-function relationships in this tissue and of the evolution and true diversity of cartilage and bone.

Structural and mechanical properties of fish scales for the bio-inspired design of flexible body armors: A review

Natural protection offered to living beings is the result of millions of years of biological revolution. The protections provided in fishes, armadillos, and turtles by unique hierarchal designs help them to survive in surrounding environments. Natural armors offer protections with outstanding mechanical properties, such as high penetration resistance and toughness to weight ratio. The mechanical properties are not the only key features that make scales unique; they are also highly flexible and breathable. In this study, we aim to review the structural and mechanical characteristics of the scales from ray-finned or teleost fishes, which can be used for new bio-inspired armor designs. It is also essential to consider the hierarchical structure of extinct and existing natural armors. The basic characteristics, as mentioned above, are the foundation for developing high-performance, well-structured flexible natural armors. Furthermore, the present review justifies the importance of interaction between toughness, hardness, and deformability in well-engineered bio-inspired body armor. At last, some suggestions are proposed for the design and fabrication of new bio-inspired flexible body armors.

Bending behavior of biomimetic scale covered beam with tunable stiffness scales

Biomimetic scales provide a convenient template to tailor the bending stiffness of the underlying slender substrate due to their mutual sliding after engagement. Scale stiffness can therefore directly impact the substrate behavior, opening a potential avenue for substrate stiffness tunability. Here, we have developed a biomimetic beam, which is covered by tunable stiffness scales. Scale tunability is achieved by specially designed plate like scales consisting of layers of low melting point alloy (LMPA) phase change materials fully enclosed inside a soft polymer. These composite scales can transition between stiff and soft states by straddling the temperatures across LMPA melting points thereby drastically altering stiffness. We experimentally analyze the bending behavior of biomimetic beams covered with tunable stiffness scales of two architectures—one with single enclosure of LMPA and one with two enclosures of different melting point LMPAs. These architectures provide a continuous stiffness change of the underlying substrate post engagement, controlled by the operating temperature. We characterize this response using three-point bending experiments at various temperature profiles. Our results demonstrate for the first time, the pronounced and reversible tunability in the bending behavior of biomimetic scale covered beam, which are strongly dependent on the scale material and architecture. Particularly, it is shown that the bending stiffness of the biomimetic scale covered beam can be actively and reversibly tuned by a factor of up to 7. The developed biomimetic beam has applications in soft robotic grippers, smart segmented armors, deployable structures and soft swimming robots.

Bioinspired hierarchical impact tolerant materials

The quest for new light-weight materials with superior mechanical properties is a goal of materials scientists and engineers worldwide. A promising route in this pursuit is drawing inspiration from nature to design and develop materials with enhanced properties. By emulating the graded mineral content and hierarchical structure of fish scales of the Arapaima gigas from the nano to macro scales, we were able to develop bioinspired laminated composites with improved impact resistance. Activated by the addition of nano-particles of Al₂O₃ and nano-layers of TiN to a thermoplastic fiber substrate, new energy dissipation mechanisms operating at the nanoscale enhanced the energy absorption and stiffness of the bioinspired material. Remarkably, the newly developed materials are easily transferred to the industry with minimum associated manufacturing costs.

Multiscale Toughening Mechanisms in Biological Materials and Bioinspired Designs

Biological materials found in Nature such as nacre and bone are well recognized as light-weight, strong, and tough structural materials. The remarkable toughness and damage tolerance of such biological materials are conferred through hierarchical assembly of their multiscale (i.e., atomic- to macroscale) architectures and components. Herein, the toughening mechanisms of different organisms at multilength scales are identified and summarized: macromolecular deformation, chemical bond breakage, and biomineral crystal imperfections at the atomic scale; biopolymer fibril reconfiguration/deformation and biomineral nanoparticle/nanoplatelet/nanorod translation, and crack reorientation at the nanoscale; crack deflection and twisting by characteristic features such as tubules and lamellae at the microscale; and structure and morphology optimization at the macroscale. In addition, the actual loading conditions of the natural organisms are different, leading to energy dissipation occurring at different time scales. These toughening mechanisms are further illustrated by comparing the experimental results with computational modeling. Modeling methods at different length and time scales are reviewed. Examples of biomimetic designs that realize the multiscale toughening mechanisms in engineering materials are introduced. Indeed, there is still plenty of room mimicking the strong and tough biological designs at the multilength and time scale in Nature.

Comparative assessment of the interface between poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and fish scales in composites: Preparation, characterization, and applications

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composites containing fish scales (FSs) were prepared and used in the fabrication of three-dimensional printing filaments. Maleic anhydride (MA)-grafted polyhydroxyalkanoate (PHBV-g-MA) and FS were used to improve the compatibility of FS within a PHBV matrix. Mechanical and morphological characterization indicated that improved adhesion between FS and PHBV-g-MA enhanced the tensile strength of the composite compared with that of PHBV/FS. The PHBV-g-MA/FS composites were also more water-resistant than the PHBV/FS composites. Human foreskin fibroblasts (FBs) were seeded on two series of these composites to assess cytocompatibility. FB proliferation was greater on PHBV/FS composites than on PHBV-g-MA/FS composites. Cell-cycle assays with FBs on PHBV/FS and PHBV-g-MA/FS series composites were unaffected. Moreover, FS enhanced the antioxidant and antimicrobial properties of PHBV-g-MA/FS and PHBV/FS composites, demonstrating the potential of PHBV-g-MA/FS and PHBV/FS composites for biomedical material applications.

Bioinspirational understanding of flexural performance in hedgehog spines

In this research, the flexural performance of hedgehog spines is investigated in four ways. First, X-ray micro-computed tomography (μCT) is employed to analyze the complex internal architecture of hedgehog spines. μCT images reveal distinct structural morphology, characterized by longitudinal stringers and transverse central plates, which enhance flexural performance. Second, computer-aided design (CAD) is utilized to create and produce different three-dimensional (3D) computational models that gradually approach resemblance to hedgehog spines. Various levels of models are constructed by including and excluding key internal features of hedgehog spines, resulting in the formation of model levels from the simplest to the most realistic form. Third, finite element analysis (FEA) is exploited to simulate flexural behavior of hedgehog spines undergoing three-point bending. FEA results aim to identify and elucidate how internal structural features affect flexural stiffness and bending stress contours. Fourth, flexural analytical modeling is performed to calculate flexural shear flow and twist angle during transverse loading. The effects of the number of hedgehog outer cells, the spine wall thickness ratio and radius ratio are theoretically investigated to predict the shear stress and twist angle of the hedgehog spine structure. Results demonstrate that longitudinal stringers of the hedgehog spine significantly increase the overall flexural stiffness, while the transverse central plates provide support and rigidity to prevent spines from buckling and collapsing. Interestingly, the 3D model level that most realistically resembles the actual hedgehog spine is evidenced to have the highest specific bending stiffness, demonstrating nature's most efficient design. The findings of this study may be useful for developing hedgehog-inspired lightweight, high-stiffness, impact-tolerant structures. STATEMENT OF SIGNIFICANCE: This research has given much needed insight on the inner morphology of hedgehog spines and the structure-property relationship to the spine's flexural performance. X-ray μCT images reveal inner structural morphology, characterized by longitudinal stringers and transverse plates. Finite element analysis shows that longitudinal stringers significantly increase flexural stiffness, while the transverse plates provide support and rigidity to prevent buckling. The model that resembles the actual hedgehog spine is evidenced to have the highest specific bending stiffness, demonstrating nature's most efficient design. Analytical model studies influence on cell number, spine geometrical ratios, and further confirms nature's perfect design with lowest flexural shear flow and twist angle during transverse loading. This work paths future design for hedgehog-inspired lightweight, high-stiffness, impact-tolerant structures.

Looking deep into nature: A review of micro-computed tomography in biomimicry

Albert Einstein once said "look deep into nature, and then you will understand everything better". Looking deep into nature has in the last few years become much more achievable through the use of high-resolution X-ray micro-computed tomography (microCT). The non-destructive nature of microCT, combined with three-dimensional visualization and analysis, allows for the most complete internal and external "view" of natural materials and structures at both macro- and micro-scale. This capability brings with it the possibility to learn from nature at an unprecedented level of detail in full three dimensions, allowing us to improve our current understanding of structures, learn from them and apply them to solve engineering problems. The use of microCT in the fields of biomimicry, biomimetic engineering and bioinspiration is growing rapidly and holds great promise. MicroCT images and three-dimensional data can be used as generic bio-inspiration, or may be interpreted as detailed blueprints for specific engineering applications, i.e., reverse-engineering nature. In this review, we show how microCT has been used in bioinspiration and biomimetic studies to date, including investigations of multifunctional structures, hierarchical structures and the growing use of additive manufacturing and mechanical testing of 3D printed models in combination with microCT. The latest microCT capabilities and developments which might support biomimetic studies are described and the unique synergy between microCT and biomimicry is demonstrated. STATEMENT OF SIGNIFICANCE: This review highlights the growing use of X-ray micro computed tomography in biomimetic research. We feel the timing of this paper is excellent as there is a significant growth and interest in biomimetic research, also coupled with additive manufacturing, but still no review of the use of microCT in this field. The use of microCT for structural biomimetic and biomaterials research has huge potential but is still under-utilized, partly due to lack of knowledge of the capabilities and how it can be used in this field. We hope this review fills this gap and fuels further advances in this field using microCT.

Recent Progress in Biomimetic Additive Manufacturing Technology: From Materials to Functional Structures

Nature has developed high-performance materials and structures over millions of years of evolution and provides valuable sources of inspiration for the design of next-generation structural materials, given the variety of excellent mechanical, hydrodynamic, optical, and electrical properties. Biomimicry, by learning from nature's concepts and design principles, is driving a paradigm shift in modern materials science and technology. However, the complicated structural architectures in nature far exceed the capability of traditional design and fabrication technologies, which hinders the progress of biomimetic study and its usage in engineering systems. Additive manufacturing (three-dimensional (3D) printing) has created new opportunities for manipulating and mimicking the intrinsically multiscale, multimaterial, and multifunctional structures in nature. Here, an overview of recent developments in 3D printing of biomimetic reinforced mechanics, shape changing, and hydrodynamic structures, as well as optical and electrical devices is provided. The inspirations are from various creatures such as nacre, lobster claw, pine cone, flowers, octopus, butterfly wing, fly eye, etc., and various 3D-printing technologies are discussed. Future opportunities for the development of biomimetic 3D-printing technology to fabricate next-generation functional materials and structures in mechanical, electrical, optical, and biomedical engineering are also outlined.

3D-printing a 'family' of biomimetic models to explain armored grasping in syngnathid fishes

Seahorses and pipehorses evolved at least two independent strategies for tail grasping, despite being armored with a heavy body plating. To help explain mechanical trade-offs associated with the different designs, we created a 'family' of 3D-printed models that mimic variations in the presence and size of their armored plates. We measured the performance of the biomimetic proxies across several mechanical metrics, representative of their protective and prehensile capacities. Our results show that the models mimicking the tails of seahorses are the best all-around performers, while those of the distal-most, prehensile region of pipehorses are more flexible, but less protected. The comparison also reveals that different adaptive strategies provide different task-specific performance advantages, which could be leveraged for the design of armored manipulators or other bio-inspired technologies.

Deformation mechanics of non-planar topologically interlocked assemblies with structural hierarchy and varying geometry

Structural hierarchy is known to enhance the performance of many of Nature's materials. In this work, we apply the idea of hierarchical structure to topologically interlocked assemblies, obtained from measurements under point loading, undertaken on identical discrete block ensembles with matching non-planar surfaces. It was demonstrated that imposing a hierarchical structure adds to the load bearing capacity of topological interlocking assemblies. The deformation mechanics of these structures was also examined numerically by finite element analysis. Multiple mechanisms of surface contact, such as slip and tilt of the building blocks, were hypothesised to control the mechanical response of topological interlocking assemblies studied. This was confirmed using as a model a newly designed interlocking block, where slip was suppressed, which produced a gain in peak loading. Our study highlights the possibility of tailoring the mechanical response of topological interlocking assemblies using geometrical features of both the element geometry and the contact surface profile.