In situ synchrotron radiation µCT indentation of cortical bone: Anisotropic crack propagation, local deformation, and fracture

Marta Peña Fernández (1) , Jakob Schwiedrzik (2) , Alexander Bürki (3) , Françoise Peyrin (4) , Johann Michler (2) , Philippe K Zysset (3) , Uwe Wolfram (1)

1 EPS-HWU - School of Engineering and Physical Sciences [Edinburgh]
2 EMPA - Swiss Federal Laboratories for Materials Science and Technology [Thun]
3 ARTORG - Center for Biomedical Engineering Research
4 Imagerie Tomographique et Radiothérapie

The development of treatment strategies for skeletal diseases relies on the understanding of bone mechanical properties in relation to its structure at different length scales. At the microscale, indention techniques can be used to evaluate the elastic, plastic, and fracture behaviour of bone tissue. Here, we combined in situ high-resolution SRµCT indentation testing and digital volume correlation to elucidate the anisotropic crack propagation, deformation, and fracture of ovine cortical bone under Berkovich and spherical tips. Independently of the indenter type we observed significant dependence of the crack development due to the anisotropy ahead of the tip, with lower strains and smaller crack systems developing in samples indented in the transverse material direction, where the fibrillar bone ultrastructure is largely aligned perpendicular to the indentation direction. Such alignment allows to accommodate the strain energy, inhibiting crack propagation. Higher tensile hoop strains generally correlated with regions that display significant cracking radial to the indenter, indicating a predominant Mode I fracture. This was confirmed by the three-dimensional analysis of crack opening displacements and stress intensity factors along the crack front obtained for the first time from full displacement fields in bone tissue. The X-ray beam significantly influenced the relaxation behaviour independent of the tip. Raman analyses did not show significant changes in specimen composition after irradiation compared to non-irradiated tissue, suggesting an embrittlement process that may be linked to damage of the non-fibrillar organic matrix. This study highlights the importance of three-dimensional investigation of bone deformation and fracture behaviour to explore the mechanisms of bone failure in relation to structural changes due to ageing or disease.

Mots clés: Cortical bone; Digital volume correlation; Fracture behaviour; Indentation; Synchrotron X-ray radiation micro-computed tomography

Domaines: Biomécanique [physics.med-ph]; Imagerie; Rhumatologie et système ostéo-articulaire

Marta Peña Fernández, Jakob Schwiedrzik, Alexander Bürki, Françoise Peyrin, Johann Michler, et al.. In situ synchrotron radiation µCT indentation of cortical bone: Anisotropic crack propagation, local deformation, and fracture. Acta Biomaterialia, 2023, 167, pp.83-99. ⟨10.1016/j.actbio.2023.04.038⟩. ⟨hal-04224744⟩