Natural Biocomposites Research Articles

Nanomaterials based on natural protein fibers

Human hair and sheep wool—natural biocomposites of complex structure, composed of α-keratin chains—are analyzed as basic components for the fabrication of nanomaterials. We demonstrate that metallic nanoparticles can be immobilized both on the surface of and inside hair and wool fibers, and discuss the underlying mechanisms.

Heterogeneous chitin fibers of Tumblebug cuticle and pullout energy of dendritic fiber

Insect cuticle is a kind of natural biocomposite. There are many eximious microstructures in the cuticle which come through biologic evolution over many centuries and endow the cuticle with excellent mechanical properties. In this work, the microstructures of a Tumblebug cuticle are observed through a scanning electronic microscope (SEM). Several kinds of different fiber distributions and fiber shapes are found at the different locations of the cuticle, which may provide beneficial information to the design of high-performance synthetic composites. The maximum pullout energy of a kind of particular dendritic fibers found in the cuticle is investigated and compared with that of conventional straight fibers based on their pullout models. It indicates that the maximum pullout energy of the dendritic fiber is markedly larger than that of the conventional straight fiber, and that the more the branches of the dendritic fiber is, the more the maximum pullout energy of the dendritic fiber will increase compared to that of the conventional straight fiber, which is experimentally validated.

Structure and Gas Barrier Properties of Poly(propylene-graft-maleic anhydride)/Phosphate Glass Composites Prepared by Microlayer Coextrusion

Alternating (A−B−A)n polymer films with individual layer thicknesses in the 3−25 μm range were produced using a robust layer multiplying coextrusion process. Such a film with layers of a poly(propylene-graft-maleic anhydride) (PPgMA) alternating with layers of PPgMA containing a phosphate glass (Pglass) upon biaxial orientation exhibited percolation of high barrier filler platelets resulting in reduction in gas permeation by two to 3 orders of magnitude. This unprecedented reduction in oxygen permeability was attributed to the high volume fraction of highly aligned Pglass platelets in the polymer matrix resembling a brick wall microstructure. Biaxially oriented films with 20 vol % Pglass content exhibited a microstructure resembling alternating organic and inorganic layers, a close replica of natural biocomposites. Structural models for permeability indicated that enhanced barrier resulted from increased tortuosity of the diffusion pathway provided by the aligned high aspect ratio platelets. Aspect ratios...

Structural distortion of biogenic aragonite in strongly textured mollusc shell layers

The stabilisation of strong textures in mollusc shells has for long been a strong drawback towards precise structural determinations of these natural biocomposites. We demonstrate here on several crossed lamellar and nacre layers from two gastropods ( Charonia lampas lampas and Haliotis tuberculata tuberculata) and one bivalve ( Pinctada maxima), that on real specimens (without grinding or specific preparation), the textural information can be used efficiently for precise structural determination of the biogenic aragonite. This is done through the combination of orientation distribution function and cyclic Rietveld refinements on several hundreds to thousands of diffractions diagrams.

Enamel—A functionally graded natural coating

Objective The aim of this study is to illustrate the graded proper properties of enamel from the outer (near occlusal surface) to the inner region (near enamel–dentine junction) in a cross-sectioned surface and discuss how natural design achieve the graded functions. Methods Nanoindentation, Raman spectroscopes, and SEM were employed to compare the inner and outer regions of the cross-sectioned enamel from different angles, namely mechanical properties such as elastic modulus and hardness, indentation energy absorption ability, indentation creep ability, indentation residual stress distribution pattern, compositional differences, and microstructural differences. Results Inner enamel has lower elastic modulus and hardness but higher creep and stress redistribution abilities than outer counterpart, which is related to the gradual compositional change through the enamel. Significance Enamel can be regarded as a functionally graded natural biocomposite, which will require special attention using numerical analysis to fully appreciate the consequences of such a structure for the mechanical behaviour of teeth and restorations placed therein. Moreover, the smart design of nature can be a good model for us in functional graded materials/coatings design and development.

Thermal-Induced Wear Mechanisms of Sheet Nacre in Dry Friction

Sheet nacre is a natural biocomposite with a multiscale structure including a mineral phase of calcium carbonate (97 wt.%) and two organic matrices (3 wt.%). The mineral phase is constituted by an arrangement of CaCO3 biocrystal nanograins (ca 40 nm in size) drowned in an ‘‘intracrystalline'' organic matrix (4 nm thick) in order to form a microsized flat organomineral aragonite platelet. These platelets are themselves surrounded by an ‘‘intercrystalline'' organic matrix (40 nm thick) building up a very tough materials. This microarchitecture referred to as ‘‘bricks and mortar'' nacre structure, is mainly studied for the creation of new organic/inorganic hybrid materials. Currently, only little is known about the nacre mechanical behaviour under dynamical loading and more particularly under tribological conditions which involve shocks and thermal effects simultaneously. This paper brings out the thermal-induced damage mechanisms effect on the wear of sheet nacre by the assessment of the thermal component of the friction with a scanning thermal microscope. Results reveal that the mean contact pressure is the main driving force involved in the degradation of the organic constituents. For the lowest mean contact pressure (\0.4 MPa), wear is rather weak because the friction-induced thermal component is not sufficient for degrading the organic matrices. In contrast, beyond 0.4 MPa, the friction-induced contact temperature rises up over the melting point of the organic matrices, and may even reach the temperature of the aragonite– calcite phase transformation increasing dramatically the wear of sheet nacre.

Bond lengths differences between the mollusk-made and geological calcium carbonate

We used high-resolution neutron powder diffraction technique in order to accurately measure the atomic positions and bond lengths in calcium carbonates of biogenic (mollusk-made) and geological origin. As a result, in biogenic calcium carbonate we identified atomic bonds, first of all the C O bonds and some O O bonds, which obey significant modification (about 1%) with respect to those in geological calcium carbonate. Bond length changes are presumably due to the organic/inorganic interactions in natural bio-composites. Generally, the effect is more pronounced for aragonite, which is structurally more flexible (nine unfixed parameters in atomic positions) than calcite (one parameter of this kind only). The observed bond modifications can be a source of the reported changes in the frequencies of normal vibrations of the carbonate groups measured by Raman or Fourier-transform infrared spectroscopy (FTIR) techniques.

Biocomposite materials from flax plants: Preparation and properties

Abstract Natural biocomposite materials were prepared consisting of a crosslinked natural matrix and natural fibres. Non-woven flax fibres material was chosen as a reinforcement and mucilage polysaccharides, extracted from linseeds, were used as a matrix. The matrix was crosslinked with glutaraldehyde and glycerol was added as plasticizer. The kinetic of the sorption of the water vapour by the composite was the lowest when the material was made with mucilage extracted at 40 °C. The largest swelling was 33% for 97% of relative humidity. The best mechanical performances of the composite were also obtained when the 40 °C mucilage was used as matrix: σB = 15 MPa, eB = 8%, E = 500 MPa. The increase of both rigidity and strength might be due to the high protein content that crosslinked with glutaraldehyde. Glycerol made the composites less brittle.

Nanostructural Organization of Naturally Occurring Composites—Part I: Silica‐Collagen‐Based Biocomposites

Glass sponges, as examples of natural biocomposites, inspire investigations aiming at both a better understanding of biomineralization mechanisms and novel developments in the synthesis of nanostructured biomimetic materials. Different representatives of marine glass sponges of the class Hexactinellida (Porifera) are remarkable because of their highly flexible basal anchoring spicules. Therefore, investigations of the biochemical compositions and the micro‐ and nanostructure of the spicules as examples of naturally structured biomaterials are of fundamental scientific relevance. Here we present a detailed study of the structural and biochemical properties of the basal spicules of the marine glass sponge Monorhaphis chuni. The results show unambiguously that in this glass sponge a fibrillar protein of collagenous nature is the template for the silica mineralization in all silica‐containing structural layers of the spicule. The structural similarity and homology of collagens derived from M. chuni spicules to other sponge and vertebrate collagens have been confirmed by us using FTIR, amino acid analysis and mass spectrometric sequencing techniques. We suggest that nanomorphology of silica formed on proteinous structures could be determined as an example of biodirected epitaxial nanodistribution of amorphous silica phase on oriented fibrillar collagen templates. Finally, the present work includes a discussion relating to silica‐collagen‐based hybrid materials for practical applications as biomaterials.

Temperature dependence of electric conductivity of bamboo coral skeleton and glass sponge spicules, the marine origin biomaterials

Natural structural biomaterials of marine origin including corals and sponges provide an abundant source of novel bone and cartilage replacements. Even though mechanical and optical properties of these natural biocomposites have been treated extensively in the literature, there is no available data on their electric properties. In the paper electric conductivity along with enthalpy of the process of electric charge conduction process were determined. The conductivity–temperature (σ–T) characteristics of native and deproteinated spicules of marine glass sponge and the mineral phase of bamboo corals provide information on the process of water release and phase transition in collagen. Denaturation temperature for coral was found at 203°C. The peaks at 160° and 195°C for the native glass sponge spicules may be explained by more complicated denaturation process where probably, less ordered regions of collagen denaturated at lower temperature and regions of high crystallinity at higher temperature. The decrease in electric conductivity observed after deproteination of glass sponge spicules showed that electric charge in the native glass sponge spicules was probably transported along the paths formed by collagen. Deproteination changed also σ–T characteristics, the kink at 140°C is caused by glass transition of collagen, whereas the peak at 175°C was probably caused by thermal denaturation of residual collagen of perturbed structure.

Characterization of nanoindentation-induced residual stresses in human enamel by Raman microspectroscopy

The objective of this research was to investigate nanoindentation-induced residual stresses in human enamel using Raman microspectroscopy and establish if this approach can be used as a stress meter. Healthy human premolars and sintered hydroxyapatite samples were embedded, cut, and the surfaces were polished finely with a 0.05 microm polishing paste before Berkovich and spherical indentations were made with a force of 100 mN. Spectra were collected using a Renishaw Raman InVia reflex microscope equipped with an air-cooled charge-coupled device (CCD) camera. Sample excitation was achieved using either an argon ion laser emitting at 514.5-nm or a NIR diode laser emitting at 830-nm. The residual micro stresses within and surrounding the indentation impressions were monitored by mapping the position of the nu(1)(PO(4)) band of (crystalline) hydroxyapatite. The Raman maps coincided well with the optical micrographs of the samples. Despite the presence of a fluorescence background from the organic component of human enamel, spectra collected using 514.5-nm excitation exhibited more significant shifts in the position of the nu(1)(PO(4)) band than spectra collected using 830-nm excitation. This implies that the former excitation may be a more appropriate excitation for stress detection. It was concluded that Raman microspectroscopy provides a novel high-resolution and non-destructive method for exploring the role of microstructure on the residual stress distribution within natural biocomposites.

SEM Localization of Proteoglycans in Abalone Shell (Haliotis rufescens)

The formation of hard biomineralized tissues such as bone, teeth, exoskeletons and shells, is a well-regulated process involving control over crystal nucleation, growth, polymorphism and morphology [1]. This process involves the occurrence of a three-dimensional organic matrix framework composed of macromolecules [2]. Molusk shells are natural biocomposites formed by well-organized calcium carbonate crystals mainly in the form of calcite or aragonite. It has been postulated that the stabilization of a more unstable polymorph, such as aragonite or vaterite, depends of its interaction with the organic matrix [3, 4]. Different kind of proteins have been associated with the control of shell mineralization [5-8]. Together with proteins, a different kind of macromolecules, referred to as proteoglycans, has been demostrated to control calcium carbonate crystallization in some biomineralization models [9, 10] and suggested to be present in mollusk shells [11-14]. However, the nature of the proteoglycans involved in molusk shell structure has not been established.

Interfacial assembly of bioinspired nanostructures mediated by supersensitive crystals

Laboratory-designed biocomposites structured by organic matrices impregnated with oriented biominerals have been significantly progressed by mimicking biological processes, although several problems associated with their formulation or antigenicity remain to be solved. Here, we describe a new strategy for the formulation of bioinspired nanostructures that involves spontaneous mediation by cooperative interactions between inorganic nanocrystals and host cells without the complex procedures required for laboratory-designed biocomposites. In the present study, osteoblastic cells were cultured on hydroxyapatite and beta-tricalcium phosphate nanocrystals prepared by discharging in electrolytes. Specifically, a high level of assembly of collagenous proteins associated with cell proliferation was achieved on nanoscale beta-tricalcium phosphate crystals by catalysis of polyphosphate chains produced during cell culture. Furthermore, a spatial structure that was practically composed of natural biocomposites found in bone and teeth was obtained on the nanocrystals due to increased cross-linking between inorganic molecules and biomolecules. Suggestions for the spontaneous formulation of bioinspired nanostructures in a living body mediated by inorganic biomaterials are also discussed.

Helicoidal microstructure of Scarabaei cuticle and biomimetic research

Insect cuticles as a natural biocomposite include many favorable microstructures which have been refined over centuries and endow the cuticles excellent mechanical and physical properties, such as light weight, high strength and toughness, etc. The various microstructures of a Scarabaei cuticle are investigated with a scanning electronic microscope and reported in this paper. It is found that the cuticle is a kind of fiber-reinforced biocomposite composed of chitin-fiber layers and sclerous protein matrixes. Different chitin-fiber layers have different orientations, composed of crossed and helicoidal structures at different location. In the helicoidal structure, each fiber layer rotates with an almost fixed angle against its neighboring layer. The maximum pullout energy of the helicoidal structure is analyzed based on the representative model of the structure. The result shows that the pullout energy of the helicoidal structure is markedly larger than that of the conventional 0°-structure. A biomimetic composite with the observed helicoidal structure is designed and fabricated. A comparative test shows that the fracture toughness of the biomimetic composite is markedly larger than that of the 0°-layer composite.

Nanostructured Composites with Layered Morphology: Structure and Properties

AbstractUsing different microscopic techniques, we investigate the morphology and the micro‐deformation processes in two entirely different classes of polymer based composites: natural biocomposites and synthetic polymer composites. The emphasis has been put on the comparison of the micromechanical properties of those composite materials. In the natural layered composites exemplified by human cortical bone, analogous to the synthetic glassy polymers, craze‐like deformation zones were formed. A strong dependence of deformation mechanisms (such as transition from formation of single crazes to multiple crazing behaviour) on the layer dimension was observed in the layered composites made up of different amorphous polymers.

NANOMETER CHITIN FIBER AND LAYUP OF THE CHAFER CUTICLE

Most structural materials existing in nature take the form of a composite. After centuries of evolution, these materials have gained highly optimized microstructures and performance. In this work, a natural biocomposite, chafer cuticle, was observed with SEM, and it was found that the insect cuticle has a laminated structure with chitin fiber and protein matrix. Special helicoidal layups of chitin fibers were found with the chitin fiber being of nanometer scale. The relationship between the nanometer scale of the chitin fiber and the fracture strength of the cuticle was analyzed. The results show that the nanometer scale of the chitin fiber is profitable to maintain and improve the fracture strength of the biocomposite.

Spiry-layup model of Rutelidae cuticle

In this study, the microstructures of Rutelidae cuticle, a natural biocomposite, were observed with scanning electronic microscope (SEM). It was found that the insect cuticle has a laminated microstructure consisting of chitin fiber and protein matrix. There are particular spiry layups in the cuticle. The maximal pull-out force of the spiry layup is analyzed and compared with that of conventional 0°-layup based on their representative models. The result shows that the pull-out force of the spiry layup is markedly larger than that of the conventional 0°-layup. The corresponding experiment on the maximal pull-out forces of both spiry layup and the 0°-layup is conducted, and it shows that the maximal pull-out force of the spiry layup is markedly larger than that of the 0°-layup, which verifies and demonstrates the validity of the presented model.

Investigation of fiber configurations of chafer cuticle by SEM, mechanical modeling and test of pullout forces

Insect cuticle as a natural biocomposite includes many favored microstructures which have been refined over centuries and endow the cuticle eminent mechanical properties. This paper first studies the microstructures of chafer cuticle through SEM observations. Several peculiar fiber configurations and fiber-ply arrangements such as branched fiber, acanth-fiber and helicoid plies are observed. These microstructures are useful for man-made fiber-reinforced composites to improve their mechanical properties. Then, a special configuration of the branched fiber found in chafer cuticle is in details analyzed through a mechanical model and experimental verification. The pullout force of fibers as an index is firstly studied through parameter study. The factors, which can improve the pullout forces, are identified. Finally, the maximal pullout force of the branched fiber is experimentally tested and compared with that of plain straight fiber. It is proved that the maximal pullout force of branched fibers is obviously greater than that of the plain straight fibers.

Nanostructured artificial nacre.

Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important. Here, we demonstrate that both structural features can be reproduced by sequential deposition of polyelectrolytes and clays. This simple process results in a nanoscale version of nacre with alternating organic and inorganic layers. The macromolecular folding effect reveals itself in the unique saw-tooth pattern of differential stretching curves attributed to the gradual breakage of ionic crosslinks in polyelectrolyte chains. The tensile strength of the prepared multilayers approached that of nacre, whereas their ultimate Young modulus was similar to that of lamellar bones. Structural and functional resemblance makes clay- polyelectrolyte multilayers a close replica of natural biocomposites. Their nanoscale nature enables elucidation of molecular processes occurring under stress.