Insight into differences in nanoindentation properties of bone

Area of Science:

• Biomaterials Science
• Biomechanics
• Materials Science

Background:

• Nanoindentation is crucial for determining bone mechanical properties at the tissue level.
• Significant variations in reported bone mechanical properties exist across studies.
• Discrepancies arise from differences in bone samples, hydration, and testing parameters, hindering direct comparisons.

Purpose of the Study:

• To systematically evaluate and compare bone mechanical properties using identical samples under diverse testing conditions.
• To identify the influence of hydration state, indenter geometry, and analysis frameworks on measured properties.
• To elucidate the reasons for discrepancies in nanoindentation-derived bone property values in the literature.

Main Methods:

• Tibiae from wild type C56BL6 mice were used.
• Samples were tested in both dry and rehydrated states.
• Spherical and Berkovich indenter probes were employed, with data analyzed using elasto-plastic (Oliver-Pharr), viscoelastic, and visco-elastic-plastic models.

Main Results:

• Mean plane strain modulus values varied substantially based on hydration, probe type, and analysis method.
• Dry bone indented with a visco-elastic-plastic approach yielded ~34 GPa.
• Rehydrated bone indented with a spherical tip using viscoelastic analysis resulted in ~4 GPa, an order of magnitude lower.

Conclusions:

• Bone hydration state, indenter geometry, and analysis method assumptions significantly affect measured mechanical properties.
• Discrepancies in literature values are not solely due to bone variability but also influenced by testing and analysis protocols.
• This systematic study highlights the critical need for standardized nanoindentation protocols in bone research.