Structure Of Nacre Research Articles

Interfacial strength-controlled energy dissipation mechanism and optimization in impact-resistant nacreous structure

Nacre with a combination of superior strength and toughness is one of the best natural body armors due to its unique brick-and-mortar structure, which is recently regarded as the model system for the lightweight and high impact performance composite design. However, most of the studies of nacreous structure focused on static loadings or simple one-dimensional dynamic load. Our study presents 3D finite element simulation, 3D printing and drop-tower impact testing to reveal the role of interfacial strength and impact velocity in impact resistance of the nacreous structure. An optimal interfacial strength is observed at which the impact resistance reaches a maximum. Sorting of various evolving damage patterns demonstrates that the simultaneous intralayer radial cracks propagation and interlayer delamination lead to a maximal energy dissipation in the presence of the optimal interfacial strength. The phase diagram of damage patterns depending on interfacial strength and impact velocity reveals that the optimal interfacial strength decreases with increasing impact velocity. This study demonstrates that the impact-resistance of nacreous structure under different impact velocities can be enhanced by tuning the interfacial strength, and gives some guidance for advanced protective materials designs.

Effect of Mussel‐Inspired Poly(Dopamine)‐Functionalized Carbon Nanotubes/Graphene Nanohybrids on Interfacial Adhesion of Soy Protein‐Based Nanocomposites

The demands for strong integrated biopolymer materials have substantially increased across various industries. In this study, a biomimic strategy was proposed to prepare the poly(dopamine)‐functionalized carbon nanotubes (PDCNTs) via mussel‐inspired chemistry. The graphene dispersion was prepared in aqueous bovine serum albumin solution by ultrasonic treatment through a facile and green approach. Inspired by the excellent integration of mechanical properties and hierarchical nano/microscale structure of natural nacre, we fabricated soy isolate protein (SPI)‐based nanocomposite film with 2D graphene nanosheets and 1D surface‐functionalized PDCNTs through a layer‐by‐layer assembly process. The morphology and thickness of graphene nanosheets were analyzed by atomic force microscopy. The successful surface modification of PDCNTs was confirmed by X‐ray photoelectron spectroscopy and transmission electron microscopy. The cross‐linking hierarchical structure of the SPI hybrid film was observed in scanning electron microscopy images. A combination of multiple interfacial interactions and enhanced adhesion between the PDCNTs‐graphene conjugation and SPI matrix resulted in a remarkable improvement in the mechanical properties of the SPI‐based nanocomposites. When compared with the unmodified film, the tensile strength and elongation at break of the hybrid film were simultaneously increased by 158.93 and 78.67%, respectively. As a result of the enhanced tortuosity effect, the water vapor permeability was significantly reduced by 33.65%. In addition, the resultant film also possessed favorable water resistance, thermal stability, and ultraviolet–visible light barrier behavior. This work provided a novel bio‐inspired interfacial toughening strategy for constructing high performance biopolymer nanocomposites. POLYM. COMPOS., 40:E1649–E1661, 2019. © 2018 Society of Plastics Engineers

Tough and conductive bio-based artificial nacre via synergistic effect between water-soluble cellulose acetate and graphene

Inspired by the hierarchical structure of natural nacre, a binary artificial nacre with excellent mechanical performance, tensile strength and toughness was successfully constructed based on water-soluble cellulose acetate (WSCA) and reduced graphene oxide (rGO). The tensile strength and toughness of the hybrid films were markedly improved by the introduction of rGO, and the tensile strength and toughness of the rGO/WSCA composite films reached 499.3 MPa and 9.6 MJ/m3 (rGO-WSCA-III), respectively, which are approximately 5.0 and 5.3 times that of natural nacre. In addition, the hybrid rGO/WSCA films showed better flame retardancy and stability in water, and high electrical conductivity. In this study, we provide a strategy to design and fabricate exceptionally strong and tough artificial nacre, which has potential application in tissue engineering and as a humidity sensor.

Artificial Bicontinuous Laminate Synergistically Reinforces and Toughens Dilute Graphene Composites.

Strength and toughness are usually exclusive in polymer nanocomposites with dispersed nanofillers. This intrinsic conflict has been relieved in a high filler loading range by mimicking the nacre structure of natural selection. However, at the low loading extreme, it still remains a great challenge. Here, we design a bicontinuous lamellar (BCL) structure to synergistically reinforce and toughen nanocomposites in the dilute range of nanofiller below 1 wt %. At a typical loading of 0.3 wt %, the BCL composite of graphene oxide (GO) and poly(vinyl alcohol) (PVA) has an 8200% toughness and a comparably reinforced hardness of the dispersed counterpart, accompanying a 53-fold higher failure elongation that even exceeds that of pure PVA. Theoretical modeling and experimental analyses reveal that the continuous generation of massive crazes of GO layers endows the BCL composite with high toughness and surprising breakage elongation beyond those of pure PVA. The BCL organization is an alternatively optimal structure model to merge the exclusive strength and toughness together for damage-tolerant nanocomposites with a dilute range of nanofillers, other than nacre-like and well-dispersed structure, providing an alternative methodology to fabricate mechanically robust composites.

An aqueous-only, green route to exfoliate boron nitride for preparation of high thermal conductive boron nitride nanosheet/cellulose nanofiber flexible film

With the rapid development of electronic device, thermal management material is currently in great demand. Therefore, to design material of efficient thermal management is of high significance. In this work, we report a green route that using only water exfoliate boron nitride (BN) powder and obtain hydroxylate boron nitride nanosheets (BNNS-OH) aqueous dispersion. The BNNS-OH as high thermally conductive nanofillers composited with cellulose nanofiber (CNF) is prepared a flexible film which has high thermal conductivity, superior mechanical properties and good thermal stability. In BNNS-OH/CNF film, BNNS-OH and CNF are stacked layer-by-layer to form a natural nacre structure, where CNF acted as the mortar filled in the interlayer space. The in-plane thermal conductivity of the 25 wt%BNNS-OH/CNF film is 22.67 W m−1 K−1, corresponding to thermal boundary resistance is 3.26 × 10−6 m2 kW−1 calculated by the Maxwell-Garnett effective medium theory (EMT) which is lower than that by previously reported methods. We demonstrate the potential usefulness of BNNS-OH/CNF film in electronic device-cooling application.

Inside Back Cover: Laser imaging polarimetry of nacre (J. Biophotonics 10/2018)

Nacre, or mother of pearl, is a complex self‐assembled biomaterial that has high resistance against breakage. It is made of micronsized aragonite‐crystal tablets embedded in organic matter, in a brick‐and‐mortar type of structure. Analysis of the transformation of polarized light passing through this natural structure reveals the great uniformity of the layered arrangement of bivalve nacre (left image), and quite distinctly, the non‐uniform columnar structure of gastropod nacre (right image).Further details can be found in the article by Joshua A. Jones, Rebecca A. Metzler, Anthony J. D'Addario et, al. (e201800026). image

Thin Nacre-Biomimetic Coating with Super-Anticorrosion Performance.

The rigorous organic and inorganic laminated structure of nacre has been developed by millions of years of biological evolution against various external impacts, including mechanical loadings and chemical attacks. Nacre-biomimetic materials have been recognized as an effective strategy to achieve high strength and toughness simultaneously. However, the understanding of nacre-like structure from the perspective of corrosion protection is still very limited. This work investigates the anticorrosion performance of nacre-biomimetic GO/epoxy (NBGE) coatings with alternating layers. Potentiodynamic polarization measurements indicated that the corrosion rate of steel protected by the NBGE coating with 5 layers of GO and 6 layers of epoxy (5NBGE) and a total thickness of 17 μm was 20 times slower than that of steel under the pure epoxy coating twice as thick in 3.5 wt % NaCl solution. Electrochemical impedance spectroscopy measurements revealed the importance and functions of the GO layers in NBGE coatings. The 5NBGE coating exhibited better performance than carbon-based nanoparticle/epoxy mixed coatings. The superior anticorrosion performance of the NB5G6E coating was supported by photographic observations, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chloride diffusion measurements. The strong cross-linking layer-by-layer structure of NBGE coatings was proved by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analyses. The anticorrosion mechanism of the NBGE coatings was interpreted by the mitigation of chemical reactions occurring at the steel-coating interface due to the restricted intrusion of O2, H2O, and Cl- through the reduced pores and defects by the intercalated GO layers in the coatings.

Artificial Nacre from Supramolecular Assembly of Graphene Oxide.

Inspired by the "brick-and-mortar" structure and remarkable mechanical performance of nacre, many efforts have been devoted to fabricating nacre-mimicking materials. Herein, a class of graphene oxide (GO) based artificial nacre material with quadruple hydrogen-bonding interactions was fabricated by functionalization of polydopamine-capped graphene oxide (PDG) with 2-ureido-4[1 H]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units followed by supramolecular assembly process. The artificial nacre displays a strict "brick-and-mortar" structure, with PDG nanosheets as the brick and UPy units as the mortar. The resultant nanocomposite shows an excellent balance of strength and toughness. Because of the strong strengthening via quadruple hydrogen bonding, the tensile strength and toughness can reach 325.6 ± 17.8 MPa and 11.1 ± 1.3 MJ m-3, respectively, thus exceeding natural nacre, and reaching 3.6 and 10 times that of a pure GO artificial nacre. Furthermore, after further H2O treatment, the resulting H2O-treated PDG-UPy actuator displays significant bending actuations when driven by heat. This work provides a pathway for the development of artificial nacre for their potential applications in energy conversion, temperature sensor, and thermo-driven actuator.

A Hydrogel-Film Casting to Fabricate Platelet-Reinforced Polymer Composite Films Exhibiting Superior Mechanical Properties.

The fabrication of mechanically superior polymer composite films with controllable shapes on various scales is difficult. Despite recent research on polymer composites consisting of organic matrices and inorganic materials with layered structures, these films suffer from complex preparations and limited mechanical properties that do not have even integration of high strength, stiffness, and toughness. Herein, a hydrogel-film casting approach to achieve fabrication of simultaneously strong, stiff, and tough polymer composite films with well-defined microstructure, inspired from a layer-by-layer structure of nacre is reported. Ca2+ -crosslinked alginate hydrogels incorporated with platelet-like alumina particles are dried to form composite films composed of horizontally aligned alumina platelets and alginate matrix with uniformly layered microstructure. Alumina platelets are evenly distributed parallel without precipitations and contribute to synergistic enhancements of strength, stiffness and toughness in the resultant film. Consequentially, Ca2+ -crosslinked alginate/alumina (Ca2+ -Alg/Alu) films show exceptional tensile strength (267 MPa), modulus (17.9 GPa), and toughness (3.60 MJ m-3 ). Furthermore, the hydrogel-film casting allows facile preparation of polymer composite films with controllable shapes and various scales. The results suggest an alternative approach to design and prepare polymer composites with the layer-by-layer structure for superior mechanical properties.

A Nacre-Like Carbon Nanotube Sheet for High Performance Li-Polysulfide Batteries with High Sulfur Loading.

Lithium‐sulfur (Li‐S) batteries are considered as one of the most promising energy storage systems for next‐generation electric vehicles because of their high‐energy density. However, the poor cyclic stability, especially at a high sulfur loading, is the major obstacles retarding their practical use. Inspired by the nacre structure of an abalone, a similar configuration consisting of layered carbon nanotube (CNT) matrix and compactly embedded sulfur is designed as the cathode for Li‐S batteries, which are realized by a well‐designed unidirectional freeze‐drying approach. The compact and lamellar configuration with closely contacted neighboring CNT layers and the strong interaction between the highly conductive network and polysulfides have realized a high sulfur loading with significantly restrained polysulfide shuttling, resulting in a superior cyclic stability and an excellent rate performance for the produced Li‐S batteries. Typically, with a sulfur loading of 5 mg cm−2, the assembled batteries demonstrate discharge capacities of 1236 mAh g−1 at 0.1 C, 498 mAh g−1 at 2 C and moreover, when the sulfur loading is further increased to 10 mg cm−2 coupling with a carbon‐coated separator, a superhigh areal capacity of 11.0 mAh cm−2 is achieved.

Effects of tablet waviness on the mechanical response of architected multilayered materials: Modeling and experiment

The excellent mechanical properties that biological materials possess are greatly influenced by the geometrical properties of their small scale constituents. Nacre, also known as Mother of Pearl, is an organic-inorganic composite material that makes up the inner layer of seashells. Nacre is observed for its impressive combination of stiffness, strength, and toughness which can be attributed to its waviness and the layering pattern of the brick and mortar structure of ceramic and protein that allows nacre to exhibit great mechanical energy and dissipate it over a large volume. In this study, the effect of this waviness on a model architected multilayered material system is analyzed numerically and experimentally in order to understand its effects on the stiffness, strength, and toughness of nacre. 3-D printed composites with auxetic and nacreous structure were created and tested in tensile boundary conditions. Finite element analysis was used to study the stress distribution and mechanical response of these composites. Results from the finite element models and the mechanical tests results show that increasing the tablet’s waviness increases the stiffness, however, there is an optimum value of tablet waviness for the highest strength and tensile toughness. Increasing waviness level can improve the elastic modulus by about 23%, strength by about 65% and toughness by about 42%. Using the proposed modeling approach, more detailed studies can be done on the toughening mechanisms of composite multilayered materials. These results can be used as a guide to design super-tough composites with multilayered structures.

An extended analytic model for the elastic properties of platelet-staggered composites and its application to 3D printed structures

The load transfer mechanism in the unique staggered platelet structure of nacre has been intensively analyzed, and its structural features have been mimicked by various manufacturing methods such as 3D printing. However, due to the limited applicability of most analytical models and the limitations of 3D printers, it remains difficult to quantitatively predict and design the properties of nacre-inspired synthetic structures. In this study, we improve the analytic models to predict the effective elastic properties of various staggered platelet structures for a wide range of constituent materials’ elastic moduli and geometric parameters by carefully accounting for the volume average of elastic properties. We also systematically investigate the effect of the printing orientation and width of the composite structure fabricated by a 3D printer. We show that our improved analytic model accurately predicts the properties of a 3D printed composite when the manufacturing-condition-dependent material properties are used as input. Our study reveals the origin of discrepancy between theory and 3D printed structures and enables a rational design of nacre-inspired structures.

Nacre-mimic Reinforced Ag@reduced Graphene Oxide-Sodium Alginate Composite Film for Wound Healing

With the emerging of drug-resistant bacterial and fungal pathogens, there raise the interest of utilizing versatile antimicrobial biomaterials to treat the acute wound. Herein, we report the spraying mediated assembly of a bio-inspired Ag@reduced graphene-sodium alginate (AGSA) composite film for effective wound healing. The obtained film displayed lamellar microstructures similar to the typical “brick-and-mortar” structure in nacre. In this nacre-mimic structure, there are abundant interfacial interactions between nanosheets and polymeric matrix, leading to remarkable reinforcement. As a result, the tensile strength, toughness and Young’s modulus have been improved 2.8, 2.3 and 2.7 times compared with pure sodium alginate film, respectively. In the wound healing study, the AGSA film showed effective antimicrobial activities towards Pseudomonas aeruginosa, Escherichia coli and Candida albicans, demonstrating the ability of protecting wound from pathogenic microbial infections. Furthermore, in vivo experiments on rats suggested the effect of AGSA film in promoting the recovery of wound sites. According to MTT assays, heamolysis evaluation and in vivo toxicity assessment, the composite film could be applied as a bio-compatible material in vitro and in vivo. Results from this work indicated such AGSA film has promising performance for wound healing and suggested great potential for nacre-mimic biomaterials in tissue engineering applications.

Transformation of ACC into aragonite and the origin of the nanogranular structure of nacre

Currently a basic tenet in biomineralization is that biominerals grow by accretion of amorphous particles, which are later transformed into the corresponding mineral phase. The globular nanostructure of most biominerals is taken as evidence of this. Nevertheless, little is known as to how the amorphous-to-crystalline transformation takes place. To gain insight into this process, we have made a high-resolution study (by means of transmission electron microscopy and other associated techniques) of immature tablets of nacre of the gastropod Phorcus turbinatus, where the proportion of amorphous calcium carbonate is high. Tablets displayed a characteristic nanoglobular structure, with the nanoglobules consisting of an aragonite core surrounded by amorphous calcium carbonate together with organic macromolecules. The changes in composition from the amorphous to the crystalline phase indicate that there was a higher content of organic molecules within the former phase. Within single tablets, the crystalline cores were largely co-oriented. According to their outlines, the internal transformation front of the tablets took on a complex digitiform shape, with the individual fingers constituting the crystalline cores of nanogranules. We propose that the final nanogranular structure observed is produced during the transformation of ACC into aragonite.

Nacre-inspired design of CFRP composite for improved energy absorption properties

Discontinuous unidirectional fiber-reinforced composites are shown to possibly exhibit pseudo-ductile failure that is lacking in continuous fiber composites. The aim of this paper is to use a discontinuous and interdigitated design strategy which mimicks the nacre structure to improve the specific energy absorption (SEA) of a carbon/expoxy composite tube. Quasi-static axial compressive experiment is combined with a digital image correlation system to analyze the failure process of the specimens. Four kinds of tubular specimens which are based on different ply cut intervals and distributions are fabricated and crushed. The load-crushed displacement curves and the SEA values are obtained showing that circular shaped continuous ply cuts result is the highest fluctuation of the compressive force. Moreover, the tubes with helical and nacre mimicking ply cut structures result in a flatter load-crushed displacement curve. This work demonstrates that in a crush process, unidirectional composites with a well-designed discontinuity at the ply level can improve the SEA over 51% as compared to the unidirectional continuous tubes.

Review on 3D Prototyping of Damage Tolerant Interdigitating Brick Arrays of Nacre

The complex hierarchal architecture of nacre has revolutionized the field of materials science and engineering due to its unparalleled properties of strength, stiffness, damage tolerance and toughness. The characteristics of interdigitating brick and mortar structure is attributed as a conspicuous architecture for its unique combination of properties, which is organized over multiple hierarchal level from macro to nanometer in size. Despite the development of adequate methodologies such as layer-by-layer and self-assembly, imitating these physical and morphological intricacies in “one step” is still a complex and complicated phenomenon. Therefore, additive manufacturing techniques such as 3D printing can be a plausible candidate for manufacturing futuristic design concepts of composite, inspired from naturally graded functionality. In this review article, we have outlined the possibility of utilizing 3D printing technology and its challenges for bionic prototyping of nacre structure in artificial materials.

Fatigue Resistant Bioinspired Composite from Synergistic Two-Dimensional Nanocomponents.

Portable and wearable electronics require much more flexible graphene-based electrode with high fatigue life, which could repeatedly bend, fold, or stretch without sacrificing its mechanical properties and electrical conductivity. Herein, a kind of ultrahigh fatigue resistant graphene-based nanocomposite via tungsten disulfide (WS2) nanosheets is synthesized by introducing a synergistic effect with covalently cross-linking inspired by the orderly layered structure and abundant interfacial interactions of nacre. The fatigue life of resultant graphene-based nanocomposites is more than one million times at the stress level of 270 MPa, and the electrical conductivity can be kept as high as 197.1 S/cm after 1.0 × 105 tensile testing cycles. These outstanding properties are attributed to the synergistic effect from lubrication of WS2 nanosheets for deflecting crack propagation, and covalent bonding between adjacent GO nanosheets for bridging crack, which is verified by the molecular dynamics (MD) simulations. The WS2 induced synergistic effect with covalent bonding offers a guidance for constructing graphene-based nanocomposites with high fatigue life, which have great potential for applications in flexible and wearable electronic devices, etc.

Bio-Inspired nacre-like nanolignocellulose-poly (vinyl alcohol)-TiO2 composite with superior mechanical and photocatalytic properties

Nacre, the gold standard for biomimicry, provides an excellent example and guideline for assembling high-performance composites. Inspired by the layered structure and extraordinary strength and toughness of natural nacre, nacre-like nanolignocellulose/poly (vinyl alcohol)/TiO2 composites possessed the similar layered structure of natural nacre were constructed through hot-pressing process. Poly (vinyl alcohol) and TiO2 nanoparticles have been used as nanofillers to improve the mechanical performance and synchronously endow the superior photocatalytic activity of the composites. This research would be provided a promising candidate for the photooxidation of volatile organic compounds also combined with outstanding mechanical property.

Nacre-inspired design of graphene oxide–polydopamine nanocomposites for enhanced mechanical properties and multi-functionalities

Inspired by the hierarchical structure of nacre and the robust adhesive ability of mussel threads, graphene oxide–polydopamine (GO–PDA) nanocomposites are designed and synthesized to achieve enhanced mechanical properties and to provide additional functionalities. Here we report a joint experimental/computational investigation of GO–PDA nanocomposites, proposing a probable chemical reduction mechanism of PDA to convert GO to reduced GO (rGO), which helps increase the electrical conductivity. The most stable chemical connection between PDA and GO is also proposed. Our artificial nacre-like GO–PDA nanocomposites are shown to have higher tensile strength and toughness compared to natural nacre. The pulling tests conducted by molecular dynamics simulations, which are supported by our experiments, reveal that the enhanced mechanical strength of GO–PDA nanocomposites mainly originates from the additional non-covalent interactions provided by PDA. The humidity-driven shrinking mechanism of GO–PDA nanocomposites due to non-uniform stresses on the GO–PDA sheets is also discovered in our simulations and supported by our experiments. The findings in this work can help improve and tune the properties of GO–PDA nanocomposites and might also apply to other 2D materials.

Fabrication of bioinspired structured glass–ceramics with enhanced fracture toughness

Nature has the amazing ability to evolve materials with combined strength and toughness that far exceed those of their individual constituents. This study aims to develop a bioceramic that mimics the hierarchical organisation of the structure of nacre on multiple scale levels by using a widespread ceramics processing technique and bioactive components. We synthesised hexagonal-shaped platelets of β-tricalcium phosphate (β-TCP) with high aspect ratio (diagonal length of ~800 nm and thickness of ~150 nm) to mimic the aragonite (CaCO3) platelets in nacre. Bioactive glass nanoparticles (BGn, median size of 50 nm) with composition (mol%) of: B2O3 9.98, SiO2 49.02, CaO 39.64, P2O5 1.54 were fabricated to mimic bridges and asperities on the surface of platelets in nacre. Hierarchically organised structures were achieved by freeze-casting of a suspension containing β-TCP platelets and various concentrations of BGn in a custom-designed mould by adjusting the casting parameters. Results demonstrated successful self-organisation of all structural features during the freezing stage, including local alignment of platelets and entrapment of BGn between the platelets. The most significant mechanical results were obtained for nacre-structured β-TCP/5 wt% BGn sintered at an unconventionally low temperature (900 °C), which showed an indentation fracture toughness of 1.6 MPa m1/2, compared to reported values of 0.3–1.1 MPa m1/2 for β-TCP sintered at 1100–1300 °C, as well as other conventional bioceramics and glasses.