Micromechanics of osteopontin-deficient bone

Nouf  Aldegaither; Xiangli Zhong; Eduardo  Saiz; Sandra J. Shefelbine; Alexandra E. Porter; Finn  Giuliani

doi:10.55092/bm20240005

Article

Open Access

Micromechanics of osteopontin-deficient bone

Nouf Aldegaither^1,^2,³Xiangli Zhong⁴Eduardo Saiz¹Sandra J. Shefelbine⁵Alexandra E. Porter¹^,∗Finn Giuliani¹^,∗

¹ Department of Materials, Faculty of Engineering, Imperial College London, Prince Consort Road, London, UK

² College of Science and Health Professions, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia

³ King Abdullah International Medical Research Center, Riyadh, Saudi Arabia

⁴ School of Materials, University of Manchester, UK

⁵ Department of Mechanical and Industrial Engineering and Department of Bioengineering, Northeastern University, Boston, MA, USA

* a.porter@imperial.ac.uk; f.giuliani@imperial.ac.uk

Volume
Volume 2 Issue 2, 2024
Citation
Aldegaither N, Zhong X, Saiz E, Shefelbine SJ, Porter AE, et al. Micromechanics of osteopontin-deficient bone. Biofunct. Mater. 2024(2):0005, https://doi.org/10.55092/bm20240005.
DOI
10.55092/bm20240005
Copyright
Copyright2024 by the authors. Published by ELSP.

Abstract

Ageing- or bone-related diseases, such as osteoporosis leads to perturbations in the collagenous framework and mineralization that translate to deteriorated fracture resistance at the whole-bone level. However, bulk mechanical testing is insufficient to isolate the effect of these alterations on the mechanical response at a smaller length scale where molecular modifications manifest. Here, we combine in situ micromechanical testing using micropillars to determine elastic moduli, double cantilever beam mechanical tests to measure fracture toughness, and transmission electron microscopy (TEM) relate crack propagation at the microscale to local variations in collagen fibril organization. An osteopontin (OPN) knock out bone model with nanometer scale with regions of organised and disorganised collagen matrix and deteriorated fracture resistance at the whole-bone level was used to explore whether it is possible to propagate a crack in a transversely orientated pillar if the collagen fibrils in the pillar are disorganized. The average measured fracture energy for OPN-deficient mouse bone at this length scale, in the transverse direction was 0.94 ± 0.67 J/m2. This value is significantly lower than wild type bone, which we found in previous studies to be approximately 20 J/m2. TEM of cross-sections of the cracked pillars showed that the lack of OPN caused disorganization of the fibrillar network, possibly leading to deteriorated fracture resistance in bones. These preliminary findings indicate that OPN may contribute to bone’s fracture resistance through collagen matrix organization. This study serves as a starting point for more in-depth investigations that use in situ micromechanical testing using micropillars to study interplay between the ultrastructure and fracture resistance in pathologic bone.

Keywords

osteopontin; non-collagenous proteins; bone; fracture energy; toughness; collagen; double cantilever beam

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