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Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level

Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level
Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level
Limitations associated with current clinical fracture risk assessment tools highlight the need for increased understanding of the fracture mechanisms of the bone and, ideally, a means of assessing this in vivo. Being a multi-layered hierarchical structure, the overall properties of the bone are dictated by its structural and compositional properties over multiple length scales. In this study, we investigate the osteonal-, micro- and tissue-level mechanical behaviour of cortical bone tissue samples from young and elderly donors through atomic force microscope (AFM) cantilever-based nanoindentation, reference point microindentation (RPI) and fracture toughness experiments respectively. We demonstrate that bone's fracture toughness and crack growth resistance at the tissue-level are significantly correlated to damage susceptibility at the micro-level, and mechanical inhomogeneity between lamellae and interlamellar areas at the osteonal-level. In more detail, reduced nanoelasticity inhomogeneity of lamellar/interlamellar layers within the osteons correlated to increased indentation depth at the micro-level and an overall reduction in crack-growth toughness and fracture toughness of the tissue. Our data also suggest that deterioration of bone's mechanical properties is expressed concurrently at these three levels, and that mechanical inhomogeneity between the principal structural units of the cortical tissue holds a key role on bone's toughness behaviour. We hypothesise that the reduction in nanoelasticity inhomogeneity is – at least to some extent – responsible for the inability of the microstructure to effectively adapt to the applied load, e.g. by redistributing strains, in a non-catastrophic manner preventing damage formation and propagation. Our hypothesis is further supported by synchrotron radiation micro-computed tomography (SR?CT) data, which show that failure of tougher bone specimens is governed by increased deflection of the crack path and broadly spread damage around the crack-tip. In contrast, shorter and more direct crack paths as well as less-distributed damage were evidenced during failure of the weaker specimens. Overall, this multi-scale study highlights the importance of elasticity inhomogeneity within the osteon to the damage susceptibility and consequently to the fracture resistance of the tissue.
bone quality, cortical bone, damage, nanoindentation, reference point indentation, toughness
8756-3282
158-168
Katsamenis, Orestis L.
8553e7c3-d860-4b7a-a883-abf6c0c4b438
Jenkins, Thomas
e8110e1f-0b08-41ac-932a-46647c6845f3
Thurner, Philipp J.
ab711ddd-784e-48de-aaad-f56aec40f84f
Katsamenis, Orestis L.
8553e7c3-d860-4b7a-a883-abf6c0c4b438
Jenkins, Thomas
e8110e1f-0b08-41ac-932a-46647c6845f3
Thurner, Philipp J.
ab711ddd-784e-48de-aaad-f56aec40f84f

Katsamenis, Orestis L., Jenkins, Thomas and Thurner, Philipp J. (2015) Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level. Bone, 76, 158-168. (doi:10.1016/j.bone.2015.03.020). (PMID:25863123)

Record type: Article

Abstract

Limitations associated with current clinical fracture risk assessment tools highlight the need for increased understanding of the fracture mechanisms of the bone and, ideally, a means of assessing this in vivo. Being a multi-layered hierarchical structure, the overall properties of the bone are dictated by its structural and compositional properties over multiple length scales. In this study, we investigate the osteonal-, micro- and tissue-level mechanical behaviour of cortical bone tissue samples from young and elderly donors through atomic force microscope (AFM) cantilever-based nanoindentation, reference point microindentation (RPI) and fracture toughness experiments respectively. We demonstrate that bone's fracture toughness and crack growth resistance at the tissue-level are significantly correlated to damage susceptibility at the micro-level, and mechanical inhomogeneity between lamellae and interlamellar areas at the osteonal-level. In more detail, reduced nanoelasticity inhomogeneity of lamellar/interlamellar layers within the osteons correlated to increased indentation depth at the micro-level and an overall reduction in crack-growth toughness and fracture toughness of the tissue. Our data also suggest that deterioration of bone's mechanical properties is expressed concurrently at these three levels, and that mechanical inhomogeneity between the principal structural units of the cortical tissue holds a key role on bone's toughness behaviour. We hypothesise that the reduction in nanoelasticity inhomogeneity is – at least to some extent – responsible for the inability of the microstructure to effectively adapt to the applied load, e.g. by redistributing strains, in a non-catastrophic manner preventing damage formation and propagation. Our hypothesis is further supported by synchrotron radiation micro-computed tomography (SR?CT) data, which show that failure of tougher bone specimens is governed by increased deflection of the crack path and broadly spread damage around the crack-tip. In contrast, shorter and more direct crack paths as well as less-distributed damage were evidenced during failure of the weaker specimens. Overall, this multi-scale study highlights the importance of elasticity inhomogeneity within the osteon to the damage susceptibility and consequently to the fracture resistance of the tissue.

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Accepted/In Press date: 27 March 2015
e-pub ahead of print date: 9 April 2015
Published date: 1 July 2015
Keywords: bone quality, cortical bone, damage, nanoindentation, reference point indentation, toughness
Organisations: Engineering Mats & Surface Engineerg Gp, Bioengineering Group, Faculty of Engineering and the Environment

Identifiers

Local EPrints ID: 379669
URI: http://eprints.soton.ac.uk/id/eprint/379669
ISSN: 8756-3282
PURE UUID: affbee31-75a7-493e-820b-cb94b338560c
ORCID for Orestis L. Katsamenis: ORCID iD orcid.org/0000-0003-4367-4147
ORCID for Philipp J. Thurner: ORCID iD orcid.org/0000-0001-7588-9041

Catalogue record

Date deposited: 17 Aug 2015 12:26
Last modified: 18 Feb 2021 17:16

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