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Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography.
Acta Biomater 2019; 96:400-411AB

Abstract

Understanding 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

SIGNIFICANCE:

This 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.

Authors+Show Affiliations

Henry Royce Institute, School of Materials, University of Manchester, Manchester M13 9PL, UK; Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, London WC1E 7JE, UK.Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth PO1 3DJ, UK.Henry Royce Institute, School of Materials, University of Manchester, Manchester M13 9PL, UK; Geotek Ltd, 4 Sopwith Way, Daventry NN11 8PB, UK.Henry Royce Institute, School of Materials, University of Manchester, Manchester M13 9PL, UK.Henry Royce Institute, School of Materials, University of Manchester, Manchester M13 9PL, UK.Carl Zeiss X-ray Microscopy Inc., Pleasanton, CA, USA.Carl Zeiss X-ray Microscopy Inc., Pleasanton, CA, USA.Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, Portsmouth PO1 3DJ, UK.Henry Royce Institute, School of Materials, University of Manchester, Manchester M13 9PL, UK. Electronic address: p.j.withers@manchester.ac.uk.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31254684

Citation

Lu, Xuekun, et al. "Anisotropic Crack Propagation and Deformation in Dentin Observed By Four-dimensional X-ray Nano-computed Tomography." Acta Biomaterialia, vol. 96, 2019, pp. 400-411.
Lu X, Fernández MP, Bradley RS, et al. Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography. Acta Biomater. 2019;96:400-411.
Lu, X., Fernández, M. P., Bradley, R. S., Rawson, S. D., O'Brien, M., Hornberger, B., ... Withers, P. J. (2019). Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography. Acta Biomaterialia, 96, pp. 400-411. doi:10.1016/j.actbio.2019.06.042.
Lu X, et al. Anisotropic Crack Propagation and Deformation in Dentin Observed By Four-dimensional X-ray Nano-computed Tomography. Acta Biomater. 2019 Sep 15;96:400-411. PubMed PMID: 31254684.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Anisotropic crack propagation and deformation in dentin observed by four-dimensional X-ray nano-computed tomography. AU - Lu,Xuekun, AU - Fernández,Marta Peña, AU - Bradley,Robert S, AU - Rawson,Shelley D, AU - O'Brien,Marie, AU - Hornberger,Benjamin, AU - Leibowitz,Marty, AU - Tozzi,Gianluca, AU - Withers,Philip J, Y1 - 2019/06/26/ PY - 2019/04/27/received PY - 2019/06/20/revised PY - 2019/06/24/accepted PY - 2019/6/30/pubmed PY - 2019/6/30/medline PY - 2019/6/30/entrez KW - Crack shielding KW - Digital image correlation (DIC) KW - Indentation fracture KW - Ivory KW - Time-lapse imaging SP - 400 EP - 411 JF - Acta biomaterialia JO - Acta Biomater VL - 96 N2 - Understanding 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 SIGNIFICANCE: This 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. SN - 1878-7568 UR - https://www.unboundmedicine.com/medline/citation/31254684/Anisotropic_crack_propagation_and_deformation_in_dentin_observed_by_four-dimensional_X-ray_nano-computed_tomography L2 - https://linkinghub.elsevier.com/retrieve/pii/S1742-7061(19)30464-7 DB - PRIME DP - Unbound Medicine ER -