Nacre-inspired nanocomposites have attracted a great deal of attention in recent years because of their special mechanical properties and universality of the underlying principles of materials engineering. The ability to respond to external stimuli will augment the high toughness and high strength of artificial nacre-like composites and open new technological horizons for these materials. Herein, we fabricated robust artificial nacre based on montmorillonite (MMT) that combines robustness with reversible thermochromism. Our artificial nacre shows great potential in various fields such as aerospace and sensors and opens an avenue to fabricate artificial nacre responsive to other external stimuli in the future.Keywords: artificial nacre; montmorillonite; nanocomposite; robust; thermochromic;

Inspired by interfacial interactions of protein matrix and the crystal platelets in nacre, herein, a super-tough artificial nacre was produced through constructing the synergistic interface interactions of π-π interaction and hydrogen bonding between graphene oxide (GO) nanosheets and sulfonated styrene-ethylene/butylene-styrene copolymer synthesized with multifunctional benzene. The resultant GO-based artificial nacre showed super-high toughness of 15.3 ± 2.5 MJ/m3, superior to natural nacre and other GO-based nanocomposites. The ultra-tough property of the novel nacre was attributed to synergistic effect of π-π stacking interactions and hydrogen bonding. This bioinspired synergistic toughening strategy opens a new avenue for constructing high performance GO-based nanocomposites in the near future.

AbstractNatural materials, including nacre, bone, and the lobster cuticle, exhibit excellent mechanical properties, combining high strength and toughness. Such materials have the added benefit of being light in weight. These advantageous features are due to such natural materials' orderly hierarchical architectures and abundant interface interactions. How to utilize these design principles created by nature to fabricate high-performance bioinspired nanocomposites remains a great research challenge. A logical roadmap for developing these nanocomposites can be described as “discovery, invention, and creation.” Here, the discovery of the relationship between natural materials' design principles and such materials' extraordinary mechanical properties is discussed. Then, the invention of bioinspired strategies for mimicking natural materials is considered and representative strategies addressed. Next, the creation of multifunctional nanocomposites is discussed and bioinspired nanocomposites, including fiber nanocomposites, 2D film nanocomposites, and 3D bulk nanocomposites reviewed. Finally, a perspective and outlook for future directions in making bioinspired nanocomposites is provided to offer inspiration to the community and a clear vision for future research.

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The hierarchical micro/nanoscale layered formation of organic and inorganic components of natural nacre, results in abundant interfacial interactions, providing an inspiration for fabricating bioinspired nanocomposites through constructing the interfacial interactions. Herein, we demonstrated the synergistic interfacial interactions of hydrogen bonding from hydroxypropyl cellulose and ionic bonding from copper ions upon the reduced graphene oxide based bioinspired nanocomposites, which show the integrated tensile strength, toughness and excellent fatigue-resistant property, as well as high electrical conductivity. These extraordinary properties allow this kind of bioinspired nanocomposites to potentially utilize in the fields of aerospace, flexible electronics devices, etc. This study also opens a door for fabricating excellent mechanical performance graphene-based bioinspired nanocomposites via synergistic interfacial interactions in the future.

After billions of years of evolution, natural materials, such as bamboo, bone, and nacre, show unique mechanical properties, due to their intrinsic hierarchical micro/nanoscale architecture and abundant interfacial interactions. This relationship between architecture, interfacial interactions, and mechanical properties of natural materials, supplies the inspiration for constructing high performance lightweight nanocomposites. Graphene's high tensile strength, Young's modulus, and electrical conductivity when compared with other nanomaterials make it an ideal building block for constructing high performance bioinspired nanocomposites. Such nanocomposites demonstrate promise for applications in many fields, including aerospace, aeronautics, submarine devices, car, and flexible electronic devices. In this review, we focus on the bioinspired strategy for preparing graphene-based nanocomposites (GBNs), and discuss the various interfacial interactions. Then the synergistic effects from building blocks and interfacial interactions are discussed in detail, along with the resultant GBNs used in the applications of sensors, actuators, supercapacitors, and nanogenerators, are also illustrated. These GBNs include, for example, one-dimensional (1D) fiber, two-dimensional (2D) film, and three-dimensional (3D) bulk nanocomposites. Finally, we provide our perspective on GBNs, and discuss how to efficiently mimic natural materials for creating new multifunctional bioinspired nanocomposites for practical applications in the near future.

Due to the small size and special physical properties of nanometer materials, polymer nanocomposites, combined nanoscale reinforcements with polymer matrix, possess outstanding mechanical properties and functional performances, which play a key role in many fields, especially for application in fields of industry and aerospace. However, poor dispersion and weak interfacial interactions are the critical factors that restrict the great improvement in performance of polymer nanocomposites. Although these issues have been solved in some extent via various methods, such as surfactant adsorption, polymer wrapping, surface modification, it still remains a great challenge for achieving high performance polymer nanocomposites as theoretically expected. Nacre, with 95% (volume fraction) inorganic calcium carbonate and 5% (volume fraction) biopolymers, is a typical binary cooperative complementary material system with hard inorganic component and soft organic matrix. Its typical “brick-and-mortar” hierarchical micro/nano-scale structure provides an excellent guideline for constructing polymer nanocomposites. It skillfully overcomes the bottleneck of traditional approaches for fabricating polymer nanocomposites, such as poor dispersion, low loading, and weak interfacial interactions. Recently, we have successfully demonstrated the bioinspired concept is a successful approach for constructing high performance polymer nanocomposites based on different reinforcement fillers, such as nanoclay, carbon nanotubes, and graphene. The resultant bioinspired polymer nanocomposites (BPNs) show layered hierarchical micro/nano-scale structure and outstanding mechanical properties. This feature article reviews our group's work and other groups' research results on BPNs in recent years, and discuss the advantages of BPNs through comparing with traditional methods, as shown in Fig. 1, including: i) Bioinspired assembly approaches for achieving the homogeneous dispersion and layered structure of reinforcement fillers in polymer matrix, such as layer-by-layer, infiltration, evaporation, freeze casting.; ii) various approaches for designing interfacial interactions; iii) the effect of synergy on the performance of BPNs; iv) representative applications of BPNs, such as energy storage devices, filter, sensors. Finally, this feature article also focuses on a perspective of BPNs, commenting on whether the bioinspired concept is viable and practical for polymer nanocomposites, and on what has been achieved to date. Most importantly, a roadmap of BPNs for near future will be depicted, including integrated mechanical properties and functions, intelligent properties, etc.

The gold standard of natural nacre provides the inspiration for assembling bioinspired nanocomposites. Herein, the gel-film transformation method, a feasible and economical strategy, was applied to fabricate flexible, large-area, and hierarchical porous graphene oxide (GO)-based nanocomposites with excellent properties. In this study, the GO-polymer nanocomposite hydrogels could be transformed into nanocomposite films with hierarchically laminated structures via the evaporation self-assembly technique, followed by introduction of ionic cross-linking into the nanocomposite films. The obtained bioinspired nanocomposites, with synergistic effect originating from hydrogen bonds and ionic bonds, have an excellent tensile strength of 475.2 ± 13.0 MPa and a toughness of 6.6 ± 0.3 MJ m−3, as well as a high electrical conductivity of 297.1 S cm−1. Therefore, this type of strong integrated nacre-like graphene nanocomposites have great potential applications in aerospace and flexible supercapacitor electrodes.

With its extraordinary properties as the strongest and stiffest material ever measured and the best-known electrical conductor, graphene could have promising applications in many fields, especially in the area of nanocomposites. However, processing graphene-based nanocomposites is very difficult. So far, graphene-based nanocomposites exhibit rather poor properties. Nacre, the gold standard for biomimicry, provides an excellent example and guidelines for assembling two-dimensional nanosheets into high performance nanocomposites. The inspiration from nacre overcomes the bottleneck of traditional approaches for constructing nanocomposites, such as poor dispersion, low loading, and weak interface interactions. This tutorial review summarizes recent research on graphene-based artificial nacre nanocomposites and focuses on the design of interface interactions and synergistic effects for constructing high performance nanocomposites. This tutorial review also focuses on a perspective of the dynamic area of graphene-based nanocomposites, commenting on whether the concept is viable and practical, on what has been achieved to date, and most importantly, what is likely to be achieved in the future.

Inspired by the relationship between interface interactions and the high performance mechanical properties of nacre, a strong and tough nacre-inspired nanocomposite was demonstrated based on graphene oxide (GO) and polyacrylic acid (PAA) prepared via a vacuum-assisted filtration self-assembly process. The abundant hydrogen bonding between GO and PAA results in both high strength and toughness of the bioinspired nanocomposites, which are 2 and 3.3 times higher than that of pure reduced GO film, respectively. In addition, the effect of environmental relative humidity on the mechanical properties of bioinspired nanocomposites is also investigated, and is consistent with previous theoretical predictions. Moreover, this nacre-inspired nanocomposite also displays high electrical conductivity of 108.9 S cm−1. These excellent physical properties allow this type of nacre-inspired nanocomposite to be used in many applications, such as flexible electrodes, aerospace applications, and artificial muscles etc. This nacre-inspired strategy also opens an avenue for constructing integrated high performance graphene-based nanocomposites in the near future.

Inspired by the nacre, we demonstrated the integrated ternary artificial nacre nanocomposites through synergistic toughening of graphene oxide (GO) and nanofibrillar cellulose (NFC). In addition, the covalent bonding was introduced between adjacent GO nanosheets. The synergistic toughening effects from building blocks of one-dimensional NFC and two-dimensional GO, interface interactions of hydrogen and covalent bonding together result in the integrated mechanical properties including high tensile strength, toughness, and fatigue life as well as high electrical conductivity. These extraordinary properties of the ternary synthetic nacre nanocomposites allow the support for advances in diverse strategic fields including stretchable electronics, transportation, and energy. Such bioinspired strategy also provides a new insight in designing novel multifunctional nanocomposites.Keywords: bioinspired; graphene oxide; mechanical properties; nanofibrillar cellulose; ternary artificial nacre

Natural nacre exhibits extraordinary strong and tough properties with its brick-and-mortar structure that was perfected after millions of years of evolution. Inspired by nacre's hierarchical structure, we fabricated multifunctional bioinspired nanocomposites of graphene oxide (GO) and montmorillonite (MMT) nanosheets with poly(vinyl alcohol) (PVA) via a vacuum-assisted filtration self-assembly process. By combining graphene oxide and montmorillonite with PVA, we demonstrated an effective synergistic toughening effect and obtained integrated strong and tough bioinspired nanocomposites. Furthermore, these nanocomposites show high fatigue-resistant properties, high electrical conductivity and good fire retardant properties. As such, they have promising potential in many applications, including flexible electrodes, flame retardant insulation and as aerospace materials. The technique developed here provides new insights for designing nanocomposites with a complex hierarchical structure that mimic nacre.

Inspired by the nano/micro-scale hierarchical structure of nacre, we developed a new method for fabricating highly electrically conductive graphene–epoxy layered composites. In this new method, the graphene loading can be easily controlled, and the intrinsic three-dimensional network of graphene in the composites results in high electrical conductivity. Through effective surface modification, the interface strength between graphene and epoxy matrix was dramatically improved, leading to the 23-fold improvement in tensile strength, 136-fold in Young's modulus, and 8-fold in electrical conductivity compared with the pure graphene foam. These high performance bioinspired graphene–epoxy layered composites have a great potential for applications in electromagnetic interference (EMI) shielding, aerospace, and other electrical devices.

Natural nacre supplies a number of properties that can be used in designing high-performance bioinspired materials. Likewise, due to the extraordinary properties of graphene, a series of bioinspired graphene-based materials have recently been demonstrated. Compared to other approaches for constructing graphene-based materials, bioinspired concepts result in high-loading graphene, and the resultant high-performance graphene-based artificial nacres demonstrate isotropic mechanical and electrical properties. In this Perspective, we describe how to construct integrated graphene-based artificial nacre through the synergistic relationship between interface interactions and building blocks. These integrated graphene-based artificial nacres show promising applications in many fields, such as aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.Keywords: bioinspired; graphene; integrated materials; nacre;

Graphene is the strongest and stiffest material, leading to the development of promising applications in many fields. However, the assembly of graphene nanosheets into macrosized nanocomposites for practical applications remains a challenge. Nacre in its natural form sets the “gold standard” for toughness and strength, which serves as a guide to the assembly of graphene nanosheets into high-performance nanocomposites. Here we show the strong, tough, conductive artificial nacre based on graphene oxide through synergistic interactions of hydrogen and covalent bonding. Tensile strength and toughness was 4 and 10 times higher, respectively, than that of natural nacre. The exceptional integrated strong and tough artificial nacre has promising applications in aerospace, artificial muscle, and tissue engineering, especially for flexible supercapacitor electrodes due to its high electrical conductivity. The use of synergistic interactions is a strategy for the development of high-performance nanocomposites.Keywords: artificial nacre; chitosan; graphene oxide; synergistic interaction;

With its synergistic toughening effect and hierarchical micro/nanoscale structure, natural nacre sets a “gold standard” for nacre-inspired materials with integrated high strength and toughness. We demonstrated strong and tough ternary bioinspired nanocomposites through synergistic toughening of reduced graphene oxide and double-walled carbon nanotube (DWNT) and covalent bonding. The tensile strength and toughness of this kind of ternary bioinspired nanocomposites reaches 374.1 ± 22.8 MPa and 9.2 ± 0.8 MJ/m3, which is 2.6 and 3.3 times that of pure reduced graphene oxide film, respectively. Furthermore, this ternary bioinspired nanocomposite has a high conductivity of 394.0 ± 6.8 S/cm and also shows excellent fatigue-resistant properties, which may enable this material to be used in aerospace, flexible energy devices, and artificial muscle. The synergistic building blocks with covalent bonding for constructing ternary bioinspired nanocomposites can serve as the basis of a strategy for the construction of integrated, high-performance, reduced graphene oxide (rGO)-based nanocomposites in the future.Keywords: double-walled carbon nanotube; graphene oxide; integrated; synergistic toughening; ternary bioinspired nanocomposite;

Inspired by the ternary structure of natural nacre, robust ternary artificial nacre is constructed through synergistic toughening of graphene oxide (GO) and molybdenum disulfide (MoS2) nanosheets via a vacuum-assisted filtration self-assembly process. The synergistic toughening effect from high mechanical properties of GO and lubrication of MoS2 nanosheets is successfully demonstrated. Meanwhile, the artificial nacre shows high electrical conductivity. This approach for constructing robust artificial nacre by synergistic effect from GO and MoS2 provides a creative opportunity for designing and fabricating integrated artificial nacre in the near future, and this kind of ternary artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.Keywords: graphene oxide; mechanical properties; molybdenum disulfide; synergistic toughening; ternary artificial nacre;

Nature has inspired researchers to construct structures with ordered layers as candidates for new materials with high mechanical performance. As a prominent example, nacre, also known as mother of pearl, consists of a combination of inorganic plates (aragonite calcium carbonate, 95% by volume) and organic macromolecules (elastic biopolymer, 5% by volume) and shows a unique combination of strength and toughness. Investigations of its structure reveal that the hexagonal platelets of calcium carbonate and the amorphous biopolymer are alternatively assembled into the orderly layered structure. The delicate interface between the calcium carbonate and the biopolymer is well defined. Both the building blocks that make up these assembled layers and the interfaces between the inorganic and organic components contribute to the excellent mechanical property of natural nacre.In this Account, we summarize recent research from our group and from others on the design of bioinspired materials composed by layering various primitive materials. We focus particular attention on nanoscale carbon materials. Using several examples, we describe how the use of different combinations of layered materials leads to particular properties. Flattened double-walled carbon nanotubes (FDWCNTs) covalently cross-linked in a thermoset three-dimensional (3D) network produced the materials with the highest strength. The stiffest layered materials were generated from borate orthoester covalent bonding between adjacent graphene oxide (GO) nanosheets, and the toughest layered materials were fabricated with Al2O3 platelets and chitosan via hydrogen bonding. These new building blocks, such as FDWCNTs and GO, and the replication of the elaborate micro-/nanoscale interface of natural nacre have provided many options for developing new high performance artificial materials.The interface designs for bioinspired layered materials are generally categorized into (1) hydrogen bonding, (2) ionic bonding, and (3) covalent bonding. Using these different strategies, we can tune the materials to have specific mechanical characteristics such as high strength, excellent strain resistance, or remarkable toughness. Among these design strategies, hydrogen bonding affords soft interfaces between the inorganic plates and the organic matrix. Covalent cross-linking forms chemical bonds between the inorganic plates and the organic matrix, leading to much stronger interfaces. The interfaces formed by ionic bonding are stronger than those formed by hydrogen bonding but weaker than those formed by covalent bonding.

Demands of the strong integrated materials have substantially increased across various industries. Inspired by the relationship of excellent integration of mechanical properties and hierarchical nano/microscale structure of the natural nacre, we have developed a strategy for fabricating the strong integrated artificial nacre based on graphene oxide (GO) sheets by dopamine cross-linking via evaporation-induced assembly process. The tensile strength and toughness simultaneously show 1.5 and 2 times higher than that of natural nacre. Meanwhile, the artificial nacre shows high electrical conductivity. This type of strong integrated artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.Keywords: artificial nacre; bioinspired; graphene oxide; integrated high performance; mechanical properties;

Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites.Keywords: artificial nacre; bioinspired; clay; mechanical properties; synergistic toughening

Montmorillonite/poly(vinyl alcohol) (MMT/PVA) nanocomposites spanning the complete range of MMT content (0–100 wt%) are prepared by simple evaporation-induced assembly. Effects of MMT content on the structure and mechanical properties of nanocomposites are systematically investigated and exhibit two important transitions at MMT contents of 30 wt% and 70 wt%. In the range of 0–30 wt%, the nanocomposites show a random structure. With the content of PVA increasing, the mechanical properties of the resultant nanocomposites were dramatically enhanced and were higher than that by prediction according to the conventional composite model. In the range of 30–70 wt%, the nanocomposites show a nacre-like layered structure with alternating MMT platelets and PVA layers, and all PVA is completely restricted by MMT platelets. The mechanical properties of nanocomposites were further improved by increasing the content of MMT, and reached the maximum value at the MMT content of 70 wt%. The 70 wt% MMT/PVA nanocomposite has a tensile strength of 219 ± 19 MPa, which is 5.5 times higher than that of a pure PVA film and surpasses nacre and reported biomimetic layered clay/PVA composites. When the MMT content is higher than 70 wt%, the layered structure is transformed to tactoids, which deteriorate mechanical properties. These results offer comprehensive understanding for developing high-performance biomimetic layered nanocomposite materials with high nanofiller loading.

Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO3) platelets and 5 vol% elastic biopolymers), possesses a unique combination of remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organic–inorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organic–inorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).

Robust graphene-based nanocomposites show promising applications in fields of flexible, wearable and intelligent devices. But, it is still a big challenge to construct high performance macroscopic graphene-based nanocomposites for practical application through cost-efficient graphene oxide (GO) nanosheets. Inspired by the hierarchical layered structure and interfacial interactions of nacre, we demonstrated robust graphene-based nanocomposites via synergistic interfacial interactions, which are constructed via divalent ions of zinc (Zn2+), and linear molecules of 10,12-pentacosadiyn-1-ol (PCDO) with GO nanosheets. The synergistic interfacial interactions result in integrated high strength, toughness and fatigue life. Furthermore, the resultant bioinspired graphene-based nanocomposites (BGBNs) also possess high electrical conductivity. The extraordinary performance allows this kind of BGBN to be potentially utilized in aerospace, flexible electrodes of supercapacitors and other intelligent devices. The demonstration of synergistic interfacial interactions of ionic and covalent bonding also supplies an effective approach for building robust graphene-based nanocomposites in the future.

Natural nacre exhibits extraordinary strong and tough properties with its brick-and-mortar structure that was perfected after millions of years of evolution. Inspired by nacre's hierarchical structure, we fabricated multifunctional bioinspired nanocomposites of graphene oxide (GO) and montmorillonite (MMT) nanosheets with poly(vinyl alcohol) (PVA) via a vacuum-assisted filtration self-assembly process. By combining graphene oxide and montmorillonite with PVA, we demonstrated an effective synergistic toughening effect and obtained integrated strong and tough bioinspired nanocomposites. Furthermore, these nanocomposites show high fatigue-resistant properties, high electrical conductivity and good fire retardant properties. As such, they have promising potential in many applications, including flexible electrodes, flame retardant insulation and as aerospace materials. The technique developed here provides new insights for designing nanocomposites with a complex hierarchical structure that mimic nacre.

Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO3) platelets and 5 vol% elastic biopolymers), possesses a unique combination of remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organic–inorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organic–inorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).

With its extraordinary properties as the strongest and stiffest material ever measured and the best-known electrical conductor, graphene could have promising applications in many fields, especially in the area of nanocomposites. However, processing graphene-based nanocomposites is very difficult. So far, graphene-based nanocomposites exhibit rather poor properties. Nacre, the gold standard for biomimicry, provides an excellent example and guidelines for assembling two-dimensional nanosheets into high performance nanocomposites. The inspiration from nacre overcomes the bottleneck of traditional approaches for constructing nanocomposites, such as poor dispersion, low loading, and weak interface interactions. This tutorial review summarizes recent research on graphene-based artificial nacre nanocomposites and focuses on the design of interface interactions and synergistic effects for constructing high performance nanocomposites. This tutorial review also focuses on a perspective of the dynamic area of graphene-based nanocomposites, commenting on whether the concept is viable and practical, on what has been achieved to date, and most importantly, what is likely to be achieved in the future.