Research Paper
Computational and experimental methodology for site-matched investigations of the influence of mineral mass fraction and collagen orientation on the axial indentation modulus of lamellar bone

https://doi.org/10.1016/j.jmbbm.2013.07.004Get rights and content
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Highlights

  • Site-matched assessment of nanoindentation modulus, mineral mass fraction and collagen fibers orientation in human cortical bone sections.

  • Comparison of experimental nanoindentation modulus with its computed equivalent based on the site-matched morphological data.

  • While mean experimental and computed nanoindentation moduli match well, their variations exhibit very weak correlations.

  • Considering factors like nano-porosity and damage may be necessary to understand variability of lamellar stiffness of bone structural units.

  • This is not in conflict with the well known anisotropy associated with the rotated plywood model at the sublamellar scale.

Abstract

Relationships between mineralization, collagen orientation and indentation modulus were investigated in bone structural units from the mid-shaft of human femora using a site-matched design. Mineral mass fraction, collagen fibril angle and indentation moduli were measured in registered anatomical sites using backscattered electron imaging, polarized light microscopy and nano-indentation, respectively. Theoretical indentation moduli were calculated with a homogenization model from the quantified mineral densities and mean collagen fibril orientations. The average indentation moduli predicted based on local mineralization and collagen fibers arrangement were not significantly different from the average measured experimentally with nanoindentation (p=0.9). Surprisingly, no substantial correlation of the measured indentation moduli with tissue mineralization and/or collagen fiber arrangement was found. Nano-porosity, micro-damage, collagen cross-links, non-collagenous proteins or other parameters affect the indentation measurements. Additional testing/simulation methods need to be considered to properly understand the variability of indentation moduli, beyond the mineralization and collagen arrangement in bone structural units.

Keywords

Collagen fibril orientation
Nanoindentation
Homogenization
Quantitative polarized light microscopy (qPLM)
Mineralization
Site-matching

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These authors contributed equally to this paper.