Architecture of Columnar Nacre, and Implications for Its Formation Mechanism

Metzler, Rebecca A.; Abrecht, Mike; Olabisi, Ronke M.; Ariosa, D.; Johnson, Christopher; Frazer, B. H.; Coppersmith, S. N.; Gilbert, Benjamin

doi:10.1103/physrevlett.98.268102

Cited by 93 publications

(83 citation statements)

References 25 publications

(37 reference statements)

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“…Unexpectedly and unprecedentedly, these columns of co-oriented tablets start and end abruptly. A possible explanation for this architecture relies on a specific formation mechanism for nacre, as described by Metzler et al (13). In that simple static model, nucleation sites are randomly distributed on pre-existing organic matrix layers, and coorientation of tablets n+1 and n+2 is only possible if a nucleation site happens to be present between the two.…”

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Polarization-dependent imaging contrast in abalone shells

et al. 2008

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ABSTRACT. Many biominerals contain micro-or nano-crystalline mineral components, organized accurately into architectures that confer the material with improved mechanical performance at the macroscopic scale. We present here a new effect, which enables to observe the relative orientation of individual crystals at the sub-micron scale. We call it polarization-dependent imaging contrast (PIC), as it is an imaging development of the well-known x-ray linear dichroism. Most importantly PIC is obtained in situ, in pristine biominerals. We present here PIC in the prismatic and nacreous layers of Haliotis rufescens (red abalone), confirm it in geologic calcite and aragonite, and corroborate the experimental data with theoretical simulated spectra. PIC reveals new and unexpected aspects of nacre architecture that have inspired theoretical models for nacre formation.2 INTRODUCTION. Nacre, or mother-of-pearl, is intensely studied by materials scientists, mineralogists, physicists as well as chemists, because of its remarkable mechanical properties and its fascinating and poorly understood formation (1,2). Nacre is a composite of layered 400-nm thick aragonite tablets (3), and 30-nm thick organic matrix layers (4,5). Aragonite, an orthorhombic CaCO 3 polymorph, is hard but brittle. Aragonite accounts for 95% of nacre's mass, leading one to expect the mechanical characteristics of nacre to be similar to those of aragonite, yet nacre is 3000 times more resistant to fracture than aragonite (6). Materials scientists have only recently began to learn how to prepare synthetic composites outperforming their components by such large factors, and do so inspired by nacre (7,8,9,10), although not as efficiently and orderly organized as natural nacre. It is therefore of extreme interest to understand and possibly harness the mechanisms of nacre formation. Here we report unprecedented observations on the structure and architecture of nacre enabled by the use of x-ray absorption near edge (XANES) spectroscopy (11), combined with PhotoElectron Emission spectroMicroscopy (X-PEEM)(12). These observations inform and inspire new theoretical models for nacre formation mechanisms (13).

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Polarization-dependent imaging contrast in abalone shells

et al. 2008

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“…The recently developed polarization-dependent imaging contrast (PIC) displays with varying gray levels, different angles between the c axis of a carbonate crystal and the X-ray polarization vector (15, 16 19). Although the method is not quantitative, it can highlight and spatially resolve regions of cooriented or misaligned crystals (15,16,19,20). Microbeam X-ray diffraction can probe volumes in the micrometer regime (10-m beam size in this work) to obtain local crystal orientation in 3-dimensions.…”

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“…X-ray photoelectron emission spectromicroscopy (X-PEEM), combined with X-ray absorption near-edge structure (XANES) spectroscopy, provide structural (13), compositional (14), and orientational (15,16) information. X-PEEM has a best resolution of 10 nm (17) (20 nm in this work) and a probing depth of a few nanometers (3 nm for carbon, 5 nm for oxygen, 12 nm for magnesium K-edges, and 3 nm for calcium L-edge) (16,18).…”

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The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Aichmayer

Paris

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools. echinoderms ͉ grinding tool ͉ self-sharpening ͉ spectromicroscopy ͉ X-ray microdiffraction

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“…However, synchrotron spectromicroscopy and X-ray absorption near-edge structure spectroscopy measurements suggest that individual tablets behave as single crystals under polarized X-ray illumination, and the nanograins are all co-oriented within each tablet (Metzler et al 2007). The same authors showed that the growth direction of such crystal is not oriented parallel to the c-axis of the individual tablet and that there are columns of co-oriented tablets, with the number of tablets per co-oriented column varying between 1 and 40.…”

Section: Structure Of Nacrementioning

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Biomimetic design of materials and biomaterials inspired by the structure of nacre

Luz

Mano

2009

Phil. Trans. R. Soc. A.

203

138

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The micro-architecture of nacre (mother of pearl) has been classically illustrated as a 'brick-and-mortar' arrangement. It is clear now that hierarchical organization and other structural features play an important role in the amazing mechanical properties of this natural nanocomposite. The more important structural characteristics and mechanical properties of nacre are exposed as a base that has inspired scientists and engineers to develop biomimetic strategies that could be useful in areas such as materials science, biomaterials development and nanotechnology. A strong emphasis is given on the latest advances on the synthetic design and production of nacre-inspired materials and coatings, in particular to be used in biomedical applications.

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Architecture of Columnar Nacre, and Implications for Its Formation Mechanism

Cited by 93 publications

References 25 publications

Polarization-dependent imaging contrast in abalone shells

Polarization-dependent imaging contrast in abalone shells

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Biomimetic design of materials and biomaterials inspired by the structure of nacre

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