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Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials. Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers. The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures. In particular, the double-Bouligand architecture can effectively deflect cracking paths, alleviate strain localization, and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite, representing a successful implementation of the property-optimizing mechanisms in fish scales. The strength of the composites, specifically the effect of their bioinspired architectures, was interpreted based on the adaptation of classical laminate theory. This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.

The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials; nevertheless, it is challenging to reproduce in metals. Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers. These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization. The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures. In particular, under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening, stretching, interfacial sliding with the matrix, and the cooperative kinking deformation of fiber grids, representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness. This study may serve to promote the development of new high-performance tungsten-copper composites for applications, e.g., as electrical contacts or heat sinks, and offer a viable approach for constructing bioinspired architectures in metallic materials.

Bioinspired nacre-like structures are effective in toughening materials, yet are difficult to construct in Mg-ceramic systems. Here, a set of Mg-MAX phase composites with nacre-like lamellar and brick-and-mortar architectures were fabricated by pressureless infiltration of the Mg melt into ice-templated ceramic scaffolds. The structure and mechanical properties of the composites were elucidated with a special focus on the effects of the types of architectures (lamellar or brick-and-mortar) and matrices (pure Mg or Mg alloy) on the toughening mechanisms. The nacre-like architectures were found to play a role in blunting the cracks via plastic deformation and microcracking, and shielding the cracks from applied stress by promoting crack deflection and uncracked-ligament bridging mechanisms. These composites achieved a good combination of (specific) strength and fracture toughness which are superior to other reported Mg-ceramic and nacre-like metal-ceramic composite materials.

The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions. Here we characterized the microstructure and mechanical properties of natural cornstalk pith, which has a large annual output yet lacks an effective exploitation, and evaluated its feasibility for applications as a substitute for synthetic foam materials. The cornstalk pith was revealed to be a cellular material composed of closed cells elongated along the growth direction of corn plant and reinforced by well-aligned vascular bundles penetrating the foam matrix. The compressive behavior is featured by a stable stress plateau which is favorable for energy absorption with its mechanical properties largely dependent on the hydration state and loading configuration. In particular, the initial dimension and mechanical properties of cornstalk pith can be effectively recovered after deformation simply by hydration treatment owing to swelling effect caused by the turgor pressure from osmosis. The cornstalk pith demonstrates an outstanding combination of low density and high energy absorption efficiency among various foam materials, specifically with its plateau stress and energy absorption comparable or even superior to those of some typical synthetic foam materials. These along with the huge resources and good biodegradability make it a promising natural energy absorbing cellular material for replacing synthetic counterparts.

Replicating the architecture of natural nacre has become an important approach for enhancing the damage tolerance of man-made materials. Nevertheless, this is principally limited to systems composed of chemically different constituents and demonstrates a difficulty in realizing structural hierarchy at multiple length-scales. Here a proof of concept is presented about the implementation of bioinspired nacre-like designs in a hybrid composite of pure carbon comprising its two basic allotropic forms, i.e., natural graphite flakes and amorphous carbon from the carbonization of organics. Multiscale micro/nano-architectures with three levels of hierarchy were constructed in the composite based on the preferential alignment of graphite flakes using bidirectional freeze casting method. The composite exhibited a remarkable mechanical efficiency, specifically featured by good damage tolerance with rising R-curve behavior, owing to the activation of hierarchical toughening mechanisms at micro to nano length-scales. This verifies the potency of nacre-inspired designs for generating enhanced fracture toughness in carbon systems, even using simple raw materials, which is significant for promoting their structural applications.

Porous gypsum materials are of notable significance and demonstrate a broad application in construction and biomedical engineering; nevertheless, it is challenging to simultaneously enhance their mechanical and functional properties. Here by replicating the designs of natural wood, new gypsum materials containing unidirectional micro-pores were fabricated by employing a modified ice-templating technique. The retention of ice-templated architectures was realized based on the hydration-induced self-hardening characteristic of gypsum without using the traditionally long-time freeze drying treatment. The porosities of the wood-like gypsum can be readily adjusted in wide ranges from lower than 60 vol.% to over 80 vol.% by controlling the solid loads in initial slurries. The wood-like gypsum exhibits a notable improvement in compressive strength and energy absorption efficiency along the lamellar direction by more than twofold compared to the unfrozen gypsum materials containing random pores of similar porosity. Additionally, it displays the lowest level of thermal conductivity among gypsum materials along the normal direction of lamellae, which ranges from above 0.21 to ~0.1 W (m K)−1 depending on porosity, thereby demonstrating an outstanding effectiveness for thermal insulation. It can also be easily modified from hydrophilic to hydrophobic towards enhanced water resistance. The high strength and multi-functionalities along with the feasible fabrication approach make the wood-like gypsum appealing for applications, e.g., as construction and biomedical materials. The unidirectionally open pores may also provide new possibilities for regulating the cell behavior in gypsum-based bone implants.

Progress toward developing metal implants as permanent hard-tissue substitutes requires both osteointegration to achieve load-bearing support, and energy-dissipation to prevent overload-induced bone resorption. However, in existing implants these two properties can only be achieved separately. Optimized by natural evolution, tooth-periodontal-ligaments with fiber-bundle structures can efficiently orchestrate load-bearing and energy dissipation, which make tooth-bone complexes survive extremely high occlusion loads (>300 N) for prolonged lifetimes. Here, a bioinspired peri-implant ligament with simultaneously enhanced osteointegration and energy-dissipation is presented, which is based on the periodontium-mimetic architecture of a polymer-infiltrated, amorphous, titania nanotube array. The artificial ligament not only provides exceptional osteoinductivity owing to its nanotopography and beneficial ingredients, but also produces periodontium-similar energy dissipation due to the complexity of the force transmission modes and interface sliding. The ligament increases bone-implant contact by more than 18% and simultaneously reduces the effective stress transfer from implant to peri-implant bone by ≈30% as compared to titanium implants, which as far as is known has not previously been achieved. It is anticipated that the concept of an artificial ligament will open new possibilities for developing high-performance implanted materials with increased lifespans.

Seeking strategies to enhance the overall combinations of mechanical properties is of great significance for engineering materials, but still remains a key challenge because many of these properties are often mutually exclusive. Here we reveal from the perspective of materials science and mechanics that adaptive structural reorientation during deformation, which is an operating mechanism in a wide variety of composite biological materials, functions more than being a form of passive response to allow for flexibility, but offers an effective means to simultaneously enhance rigidity, robustness, mechanical stability and damage tolerance. As such, the conflicts between different mechanical properties can be "defeated" in these composites merely by adjusting their structural orientation. The constitutive relationships are established based on the theoretical analysis to clarify the effects of structural orientation and reorientation on mechanical properties, with some of the findings validated and visualized by computational simulations. Our study is intended to give insight into the ingenious designs in natural materials that underlie their exceptional mechanical efficiency, which may provide inspiration for the development of new man-made materials with enhanced mechanical performance. STATEMENT OF SIGNIFICANCE: It is challenging to attain certain combinations of mechanical properties in man-made materials because many of these properties - for example, strength with toughness and stability with flexibility - are often mutually exclusive. Here we describe an effective solution utilized by natural materials, including wood, bone, fish scales and insect cuticle, to "defeat" such conflicts and elucidate the underlying mechanisms from the perspective of materials science and mechanics. We show that, by adaptation of their structural orientation on loading, composite biological materials are capable of developing enhanced rigidity, strength, mechanical stability and damage tolerance from constrained flexibility during deformation - combinations of attributes that are generally unobtainable in man-made systems. The design principles extracted from these biological materials present an unusual yet potent new approach to guide the development of new synthetic composites with enhanced combinations of mechanical properties.

Operating mainly as a type of weapon, the beetle horn develops an impressive mechanical efficiency based on chitinous materials to maximize the injury to opponent and simultaneously minimize the damage to itself and underlying brain under stringent loading conditions. Here the cephalic horn of the beetle Allomyrina dichotoma is probed using multiscale characterization combined with finite element simulations to explore the origins of its biomechanical functionality from the perspective of materials science. The horn is revealed to be highly regulated from the macroscopic shape, geometry, and connection with the body to the meso- and microscopic architecture, moisture content, and chemical and structural characteristics. Varying kinds of gradients are integrated at all length-scales. Such designs are demonstrated to benefit the mechanical performance by mitigating stress concentrations, retarding crack propagation, and modulating local properties to better adapt to stress. Enhanced rigidity, robustness and stability are additionally generated from the constrained flexibility endowed by the nanocomposite plywood structure through the reorientation of chitin nanofibrils within the proteinaceous matrix. These findings shed light on the intriguing materials-design strategies of nature in creating synergy of offence and persistence. They may even offer inspiration for the synthesis of high-performance materials and structures, in particular beams to resist bending and torsion.

Crustacean exoskeletons demonstrate exceptional mechanical efficiency owing to their intricate architectures. However, the translation of their underlying structural design to man-made material sys...

Brittle materials, such as oxide glasses, are usually very sensitive to flaws, giving rise to a macroscopic fracture strength that is much lower than that predicted by theory. The same applies to bulk-metallic glasses (BMGs), with the important difference that these glasses can exhibit certain plastic strain prior to the catastrophic failure. Here we consider the strongest metallic alloy known, a ternary Co55Ta10B35 BMG. We show that this macroscopically brittle glass is flaw-insensitive at the micrometer scale. This discovery emerges when the testing pre-cracked specimens with self-similar geometries, where the fracture stress does not decrease with increasing pre-crack size. The fracture toughness of this ultra-strong glassy alloy is further shown to increase with increasing sample size. Both these findings deviate from our classical understanding of fracture mechanics, and are attributed to a transition from toughness-controlled to strength-controlled fracture below a critical sample size.

Fatigue resistance is invariably critical for structural materials, but is rarely considered in the development of new bioinspired materials. Here the fatigue behavior and damage mechanisms of a nacre-like ceramic (yttria-stabilized zirconia) - polymer (polymethyl methacrylate) composite, which resembles human tooth enamel in its stiffness and hardness, were investigated under cyclic compression to simulate potential service conditions. The composite has a brick-and-mortar structure which exhibits a staircase-like fracture behavior; it displays a transition in cracking mode from intergranular splitting of ceramic bricks to separation along the inter-brick polymer phase with increasing stress amplitude. The nacre-like structure functions to induce crack deflection, increase the roughness of crack surfaces, and promote the mutual sliding between bricks during fracture; this results in high fatigue resistance, which enhances the potential of this composite for dental applications.

Taking lessons from nature offers an increasing promise toward improved performance in man‐made materials. Here new cement materials with unidirectionally porous architectures are developed by replicating the designs of natural wood using a simplified ice‐templating technique in light of the retention of ice‐templated architectures by utilizing the self‐hardening nature of cement. The wood‐like cement exhibits higher strengths at equal densities than other porous cement‐based materials along with unique multifunctional properties, including effective thermal insulation at the transverse profile, controllable water permeability along the vertical direction, and the easy adjustment to be water repulsive by hydrophobic treatment. The strengths are quantitatively interpreted by discerning the effects of differing types of pores using an equivalent element approach. The simultaneous achievement of high strength and multifunctionality makes the wood‐like cement promising for applications as new building materials, and verifies the effectiveness of wood‐mimetic designs in creating new high‐performance materials. The simple fabrication procedure by omitting the freeze‐drying treatment can also promote a better efficiency of ice‐templating technique for the mass production in engineering and may be extended to other material systems., By learning from natural wood, new cement materials with unidirectionally porous architectures are developed using a simplified ice‐templating technique. The wood‐like cement exhibits markedly higher strengths at equal densities than conventional cement materials. This is accompanied by a simultaneous achievement of multifunctional properties, including effective thermal insulation, controllable water permeability, and easy adjustment between hydrophilic and hydrophobic characteristics.

A 3D printed magnesium alloy with an interpenetrating NiTi phase shows remarkable strength, damping, and self-healing properties., It is of significance, but still remains a key challenge, to simultaneously enhance the strength and damping capacities in metals, as these two properties are often mutually exclusive. Here, we provide a multidesign strategy for defeating such a conflict by developing a Mg-NiTi composite with a bicontinuous interpenetrating-phase architecture through infiltration of magnesium melt into three-dimensionally printed Nitinol scaffold. The composite exhibits a unique combination of mechanical properties with improved strengths at ambient to elevated temperatures, remarkable damage tolerance, good damping capacities at differing amplitudes, and exceptional energy absorption efficiency, which is unprecedented for magnesium materials. The shape and strength after deformation can even be largely recovered by heat treatment. This study offers a new perspective for the structural and biomedical applications of magnesium.

The tooth enamel of vertebrates comprises a hyper-mineralized bioceramic, but is distinguished by an exceptional durability to resist impact and wear throughout the lifetime of organisms; however, enamels exhibit a low resistance to the initiation of large-scale cracks comparable to that of geological minerals based on fracture mechanics. Here we reveal that the tooth enamel, specifically from the giant panda, is capable of developing durability through counteracting the early stage of damage by partially recovering its innate geometry and structure at nano- to micro- length-scales autonomously. Such an attribute results essentially from the unique architecture of tooth enamel, specifically the vertical alignment of nano-scale mineral fibers and micro-scale prisms within a water-responsive organic-rich matrix, and can lead to a decrease in the dimension of indent damage in enamel introduced by indentation. Hydration plays an effective role in promoting the recovery process and improving the indentation fracture toughness of enamel (by ∼73%), at a minor cost of micro-hardness (by ∼5%), as compared to the dehydrated state. The nano-scale mechanisms that are responsible for the recovery deformation, specifically the reorientation and rearrangement of mineral fragments and the inter- and intra-prismatic sliding between constituents that are closely related to the viscoelasticity of organic matrix, are examined and analyzed with respect to the structure of tooth enamel. Our study sheds new light on the strategies underlying Nature's design of durable ceramics which could be translated into man-made systems in developing high-performance ceramic materials. STATEMENT OF SIGNIFICANCE: Tooth enamel plays a critical role in the function of teeth by providing a hard surface layer to resist wear/impact throughout the lifetime of organisms; however, such enamel exhibits a remarkably low resistance to the initiation of large-scale cracks, of hundreds of micrometers or more, comparable to that of geological minerals. Here we reveal that tooth enamel, specifically that of the giant panda, is capable of partially recovering its geometry and structure to counteract the early stages of damage at nano- to micro-scale dimensions autonomously. Such an attribute results essentially from the architecture of enamel but is markedly enhanced by hydration. Our work discerns a series of mechanisms that lead to the deformation and recovery of enamel and identifies a unique source of durability in the enamel to accomplish this function. The ingenious design of tooth enamel may inspire the development of new durable ceramic materials in man-made systems.

Fatigue resistance is invariably critical for structural materials, but is rarely considered in the development of new bioinspired materials. Here the fatigue behavior and damage mechanisms of a nacre-like ceramic (yttria-stabilized zirconia) - polymer (polymethyl methacrylate) composite, which resembles human tooth enamel in its stiffness and hardness, were investigated under cyclic compression to simulate potential service conditions. The composite has a brick-and-mortar structure which exhibits a staircase-like fracture behavior; it displays a transition in cracking mode from the fracture of the ceramic bricks to separation along the inter-brick polymer phase with increasing stress amplitude. The nacre-like structure functions to induce crack deflection, increase the roughness of the crack surfaces, and promote the mutual sliding between bricks during fracture; this results in high fatigue resistance, which enhances the potential of this composite for dental applications.

For composite materials applied for energy absorption and vibration/noise reduction, it is of particular significance to clarify the role of strain rate and temperature on their mechanical properties. Here we present a study on the effects of strain rate (from 10−3 s−1 to 1 s−1) and temperature (from room temperature to 350 °C) on the compressive properties of a 3-D printed Mg–NiTi interpenetrating-phase composite, which features high energy absorption efficiency and good damping capacity. Within the regimes of strain rate and temperature, the composite constantly exhibits a stable stress plateau on the stress-strain curves, yet displays markedly different damage mechanisms depending on the specific strain rate and temperature. The 3-D interpenetrating-phase architecture promotes an effective stress transfer in the composite and resists the propagation of local damages, thereby conferring a high strengthening efficiency and outstanding damage tolerance. The unique combination of mechanical properties makes the composite appealing for applications under various conditions, especially for absorbing mechanical energy and reducing vibrations and noise.

Living organisms have ingeniously evolved functional gradients and heterogeneities to create high-performance biological materials from a fairly limited choice of elements and compounds during long-term evolution and selection. The translation of such design motifs into synthetic materials offers a spectrum of feasible pathways towards unprecedented properties and functionalities that are favorable for practical uses in a variety of engineering and medical fields. Here, we review the basic design forms and principles of naturally-occurring gradients in biological materials and discuss the functions and benefits that they confer to organisms. These gradients are fundamentally associated with the variations in local chemical compositions/constituents and structural characteristics involved in the arrangement, distribution, dimensions and orientations of the building units. The associated interfaces in biological materials invariably demonstrate localized gradients and a variety of gradients are generally integrated over multiple length-scales within the same material. The bioinspired design and applications of synthetic functionally graded materials that mimic their natural paradigms are revisited and the emerging processing techniques needed to replicate the biological gradients are described. It is expected that in the future bioinspired gradients and heterogeneities will play an increasingly important role in the development of high-performance materials for more challenging applications.

Suture interfaces are one of the most common architectural designs in natural material-systems and are critical for ensuring multiple functionalities by providing flexibility while maintaining connectivity. Despite intensive studies on the mechanical role of suture structures, there is still a lack of understanding on the fracture mechanics of suture interfaces in terms of their interactions with impinging cracks. Here we reveal an interfacial toughening effect of suture structures by means of "excluding" cracks away from interfaces based on a dimensionless micro-mechanical model for single-leveled and hierarchical suture interfaces with triangular-shaped suture teeth. The effective stress-intensity driving forces for crack deflection along, versus penetration through, an interface at first impingement and on subsequent kinking are formulated and compared with the corresponding resistances. Quantitative criteria are established for discerning the cracking modes and fracture resistance of suture interfaces with their dependences on sutural tooth sharpness and interfacial toughness clarified. Additionally, the effects of structural hierarchy are elucidated through a consideration of hierarchical suture interfaces with fractal-like geometries. This study may offer guidance for designing bioinspired suture structures, especially for toughening materials where interfaces are a key weakness. STATEMENT OF SIGNIFICANCE: Suture interfaces are one of the most common architectural material designs in biological systems, and are found in a wide range of species including armadillo osteoderms, boxfish armor, pangolin scales and insect cuticles. They are designed to provide flexibility while maintaining connectivity. Despite many studies on the mechanical role of suture structures, there is still little understanding of their role in terms of interactions with impinging cracks. Here we reveal an interfacial toughening effect of suture structures by means of "excluding" cracks away from interfaces based on a dimensionless micro-mechanical model for single-leveled and hierarchical suture interfaces with triangular-shaped suture teeth. Quantitative criteria are established for discerning the cracking mode and fracture resistance of the interfaces with their dependences on sutural tooth sharpness and interfacial toughness clarified.

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.

Upon reducing the sample size into micrometer scale, an obvious brittle-to-ductile transition accompanied by a drastic change of failure mode from shattering to shear-banding was observed when compressing the brittle but strong Co55Ta10B35 bulk metallic glass (BMG). The shattering failure under macroscopic compression is dominated by splitting cracking, which completely differs from shear-banding and originates from extrinsic defects like inclusions. To reveal the critical conditions for shear-banding and splitting cracking, various micropillar specimens with intentionally introduced holes as extrinsic defects were tested, and the stress distributions at the failure moment were analyzed with finite element simulation. The shear plane criterion was found to be quite effective to estimate the nominal stress required for the failure dominated by shear-banding. However, brittle splitting cracking does not occur although the maximum tensile stress reaches the critical value, which is different from traditional brittle solids. To initiate splitting cracking, a high-tensile-stress region over a critical distance, which depends on defect size and fracture toughness of the BMG, is required. The critical conditions for shear failure and splitting cracking demonstrated in this approach can be used to estimate the failure conditions of various BMG components with complex geometries in a wide range of length scales, and to design tough composites based on brittle BMGs. As an example, a design criterion to avoid brittle splitting fracture of porous BMG materials is proposed.

The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications. However, the architectural construction of W/WC systems is challenging because of the difficulty of assembly due to their large densities. Here we present the generation of unidirectionally porous architectures, with high porosities exceeding 65%, for W and WC scaffolds using direct ice-templating techniques, which in many respects reproduce the design motif of wood. This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing. The processing, structural characteristics and mechanical properties of the resulting scaffolds were investigated and the correlations between them explored. Quantitative relationships were established to describe their strengths based on a simple model taking into account both inter- and intra-lamellar pores. The fracture mechanisms were also identified, especially in light of the porosity. This study extends the effectiveness of ice-templating techniques for systems with large densities or particle sizes. It further provides preforms for developing new nature-inspired multifunctional materials, as represented by W/WC-Cu composites.

Living organisms are adept at resisting contact deformation and damage by assembling protective surfaces with spatially varied mechanical properties, i.e. , by creating functionally graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the two prime characteristics of many biological materials to be translated into engineering design. Here, we examine one design motif from a variety of biological tissues and materials where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation over multiple length-scales, without manipulation of composition or microstructural dimension. Quantitative correlations are established between the structural orientations and local mechanical properties, such as stiffness, strength and fracture resistance; based on such gradients, the underlying mechanisms for the enhanced protective role of these materials are clarified. Theoretical analysis is presented and corroborated through numerical simulations of the indentation behavior of composites with distinct orientations. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally graded mechanical properties in synthetic materials for improved contact damage resistance. Statement of Significance Living organisms are adept at resisting contact damage by assembling protective surfaces with spatially varied mechanical properties, i.e. , by creating functionally-graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the prime characteristics of many biological materials. Here, we examine one design motif from a variety of biological tissues where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation at multiple length-scales, without changes in composition or microstructural dimension. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally-graded mechanical properties in synthetic materials for improved damage resistance.

The structural evolution of Cu45Zr45Ag10 metallic glass was investigated by in situ transmission electron microscopy heating experiments. The relationship between phase separation and crystallization was elucidated. Nucleation and growth-controlled nanoscale phase separation at early stage were seen to impede nanocrystallization, while a coarser phase separation via aggregation of Ag-rich nanospheres was found to promote the precipitation of Cu-rich nanocrystals. Coupling of composition and dynamics heterogeneities was supposed to play a key role during phase separation preceding crystallization.

Biological materials exhibit anisotropic characteristics because of the anisometric nature of their constituents and their preferred alignment within interfacial matrices. The regulation of structural orientations is the basis for material designs in nature and may offer inspiration for man-made materials. Here, how structural orientation and anisotropy are designed into biological materials to achieve diverse functionalities is revisited. The orientation dependencies of differing mechanical properties are introduced based on a 2D composite model with wood and bone as examples; as such, anisotropic architectures and their roles in property optimization in biological systems are elucidated. Biological structural orientations are designed to achieve extrinsic toughening via complicated cracking paths, robust and releasable adhesion from anisotropic contact, programmable dynamic response by controlled expansion, enhanced contact damage resistance from varying orientations, and simultaneous optimization of multiple properties by adaptive structural reorientation. The underlying mechanics and material-design principles that could be reproduced in man-made systems are highlighted. Finally, the potential and challenges in developing a better understanding to implement such natural designs of structural orientation and anisotropy are discussed in light of current advances. The translation of these biological design principles can promote the creation of new synthetic materials with unprecedented properties and functionalities.

Low-cost Fe80P12−xC8Bx (x = 0, 1, 2, 3 and 4 at.%) bulk metallic glasses (BMGs) with good soft magnetic and mechanical properties were prepared, and effects of metalloid B addition on the glass-forming ability (GFA) as well as thermal, magnetic, and mechanical properties of the BMGs were investigated. It was found that the proper B substitution for P improves the GFA of the Fe–P–C BMGs. The alloy with 2 at.% B addition manifests the highest GFA with critical diameter for glass formation of 2 mm. Besides, these BMGs exhibit good soft magnetic properties featured by high saturation magnetization of 1.35–1.57 T and low coercivity of 2.2–7.7 A/m as well as unique mechanical properties of high fracture strength of ∼3.3 GPa and visible plastic strain of 0.4%–2.5%. The combination of high GFA, good soft magnetic and mechanical properties as well as low cost makes the present Fe–P–C–B BMGs promising as soft magnetic materials for industrial applications.

Feather shaft, which is primarily featured by a cylinder filled with foam, possesses a unique combination of mechanical robustness and flexibility with a low density through natural evolution and selection. Here the hierarchical structures of peacock’s tail coverts shaft and its components are systematically characterized from millimeter to nanometer length scales. The variations in constituent and geometry along the length are examined. The mechanical properties under both dry and wet conditions are investigated. The deformation and failure behaviors and involved strengthening, stiffening and toughening mechanisms are analyzed qualitatively and quantitatively and correlated to the structures. It is revealed that the properties of feather shaft and its components have been optimized through various structural adaptations. Synergetic strengthening and stiffening effects can be achieved in overall rachis owing to increased failure resistance. This study is expected to aid in deeper understandings on the ingenious structure–property design strategies developed by nature, and accordingly, provide useful inspiration for the development of high-performance synthetic foams and foam-filled materials.

Effects of minor Sn addition on the glass-forming ability (GFA) as well as thermal, magnetic, and mechanical properties of Fe–P–C–B–Si bulk metallic glasses (BMGs) with compositions of Fe 80− x Sn x P 9 C 8 B 2 Si 1 ( x =0, 1, 2 and 3 at%) were investigated. The minor Sn substitution for Fe effectively enhances the GFA. The fully glassy rods can be produced up to 3 and 3.5 mm in diameter for the alloys with 1 and 2 at% Sn addition, respectively. Moreover, these Sn-containing BMGs exhibit good soft magnetic properties including high saturation magnetization ( M s ) of 1.46−1.51 T, low coercivity ( H c ) of 3.8−5.0 A/m and good mechanical properties, i.e., high fracture strength ( σ f ) above 3.2 GPa and limited plastic strain ( e p ) above 0.4%. The combination of large GFA, good soft magnetic and mechanical properties as well as low cost makes the Fe–Sn–P–C–B–Si BMGs promising as soft magnetic materials for industrial applications.