The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties

Albéric, Marie; Gourrier, Aurélien; Wagermaier, Wolfgang; Fratzl, Peter; Reiche, Ina

doi:10.1016/j.actbio.2018.02.016

Cited by 31 publications

(19 citation statements)

References 55 publications

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“…At the microscale, the mineralised collagen fibers are arranged essentially in cylindrical layers perpendicular to the tubules. By contrast to human dentin which has the fibrils oriented randomly within the plane of the layers in tusk they tend to be oriented within ±15°of the axial direction [13,14] (see Fig. 1d).…”

Section: Introductionmentioning

confidence: 92%

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Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

Fernández

Bradley

et al. 2019

SSRN Journal

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a b s t r a c tUnderstanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45°and 70°to the long axis of the tubules (i.e. radial to the tusk). For the 0°sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70°test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45°test-piece showed intermediate behaviour.In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. Statement of SignificanceThis paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin.

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Section: Introductionmentioning

confidence: 92%

“…The hierarchical microstructure of elephant dentin is well studied. At the mesoscale elephant dentin includes dentinal tubules that run radially from the central pulp to the periphery of the dentin following a wavy trajectory with a periodicity of $1 mm [12,13] (Fig. 1b).…”

Section: Introductionmentioning

confidence: 99%

Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

Fernández

Bradley

et al. 2019

SSRN Journal

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“…A prime advantage is to strengthen the mechanical properties along required directions considering that the applied stress/strain conditions are rarely equiaxed in practice. This is represented by the vertical alignment of nanoscale hydroxyapatite crystals in mammal tooth enamels, which helps maximize the stiffness against masticatory loads . Additionally, the anisotropic structuring gives opportunities for deriving unique functionalities in biological systems, such as robust but easily releasable adhesion and spontaneous adaptation to external stimuli …”

Section: Introductionmentioning

confidence: 99%

“…This is represented by the vertical alignment of nanoscale hydroxyapatite crystals in mammal tooth enamels, which helps maximize the stiffness against masticatory loads. [47,[71][72][73][74][75][76] Additionally, the anisotropic structuring gives opportunities for deriving unique functionalities in biological systems, such as robust but easily releasable adhesion and spontaneous adaptation to external stimuli. [77][78][79][80][81][82][83] Many engineering materials are also made anisotropic, e.g., by the development of rolling textures in metals; [84][85][86] nevertheless, their architectures are invariably far less designed with lower levels of complexity and delicacy as compared to biological systems.…”

Section: Introductionmentioning

confidence: 99%

Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

Liu

Zhang

Ritchie

2020

Adv Funct Materials

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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.

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“…These rod-shaped apatite crystals (~20-100 nm in length) surround the fibril-forming collagen molecules (~300 nm in length), which are oriented along the length of the tusk (see Figure 1). The microscopic structure of ivory includes also a three-dimensional microtubule network within the ivory matrix [16,17]. The structure of ivory is therefore similar to the dentin of teeth and bones, including human ones [18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Bio-Inspired Synthetic Ivory as a Sustainable Material for Piano Keys

2019

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Natural ivory is no longer readily or legally available, as it is obtained primarily from elephant tusks, which now enjoy international protection. Ivory, however, is the best material known for piano keys. We present a hydroxylapatite-gelatin biocomposite that is chemically identical to natural ivory but with functional properties optimized to replace it. As this biocomposite is fabricated from abundant materials in an environmentally friendly process and is furthermore biodegradable, it is a sustainable solution for piano keys with the ideal functional properties of natural ivory.

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The three-dimensional arrangement of the mineralized collagen fibers in elephant ivory and its relation to mechanical and optical properties

Cited by 31 publications

References 55 publications

Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

Bio-Inspired Synthetic Ivory as a Sustainable Material for Piano Keys

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