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Abiotic tooth enamel

Abstract

Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix1,2,3. This structural motif is unusually consistent across all species from all geological eras4,5,6. Such invariability—especially when juxtaposed with the diversity of other tissues—suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels—we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth’s normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

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Figure 1: Columnar motifs in biocomposites.
Figure 2: Schematic illustration of the preparation and structure of columnar biomimetic composites produced by sequential LBL infiltration of ZnO nanowires with polymers.
Figure 3: Mechanical properties of artificial columnar composites.
Figure 4: Dynamic mechanical properties of the artificial columnar composites.
Figure 5: Energy dissipation (tanδ) and load-bearing characteristics (E′/ρ) of (ZnO/LBL)n compared to manufactured materials and biocomposites.

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Acknowledgements

We acknowledge support from DARPA (grant HR0011-10-C-0192, MATLOG programme) and NextGen Aeronautics. We also acknowledge support from the NSF under grants ECS-0601345, CBET 0933384, CBET 0932823 and CBET 1036672. This work was also partially supported by the US Department of Defense under grant award no. MURI W911NF-12-1-0407. We thank the University of Michigan’s Electron Microscopy and Analysis Laboratory (EMAL) for assistance with electron microscopy, and the NSF for grants (numbers DMR-0320740 and DMR-9871177) funding the purchase of the JEOL 2010F analytical electron microscope used in this work. This work was supported by a National Research Foundation of Korea (NRF) grant (no. NRF-2015R1D1A1A01058029) funded by the Government of Korea (Ministry of Education). We also thank A. Jung for help with scanning electron microscopy.

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Authors

Contributions

N.A.K. and B.Y. conceived the project and designed the experiments. B.Y. and S.H.C. carried out the design and fabrication of the columnar composites and LBL films, and performed the mechanical testing experiments. T.S., A.M.W. and E.M.A. were responsible for the finite-element modelling data and assisted in the mechanical testing of the composites. N.L. was responsible for selecting the coarse grained model, and for performing molecular dynamics simulations and analysing the data. D.B. performed SEM imaging of the teeth. N.A.K., B.Y., T.S. and N.L. co-wrote the paper.

Corresponding author

Correspondence to Nicholas A. Kotov.

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The authors declare no competing financial interests.

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Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1-10, Supplementary Tables 1-2, Supplementary Comments 1-2 and additional references. (PDF 1289 kb)

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Yeom, B., Sain, T., Lacevic, N. et al. Abiotic tooth enamel. Nature 543, 95–98 (2017). https://doi.org/10.1038/nature21410

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