On the Interplay Between Roughness and Elastic Modulus at the Nanoscale: A Methodology Study with Bone as Model...

Area of Science:

• Biophysics
• Materials Science
• Nanotechnology

Background:

• Atomic force microscopy (AFM) nanoindentation is vital for subcellular mechanical analysis.
• Nanoscale elastic modulus (E) measurements are often unreliable due to unaddressed sample roughness.
• Understanding roughness influence is key to improving AFM nanoindentation accuracy.

Purpose of the Study:

• To rigorously re-examine roughness interpretation in AFM nanoindentation.
• To validate a method for extracting local roughness (γs) at each indentation site.
• To establish an accurate correlation between local roughness and elastic modulus (E) values.

Main Methods:

• Performed 80 nanoindentations on murine tibia cortical bone using two AFM tips.
• Maintained a maximum penetration depth of 10 nm for all measurements.
• Quantified local roughness (γs) at each nanoindentation site.

Main Results:

• A slight decreasing trend observed between elastic modulus (E) and local roughness (γs).
• 90% of E values were deemed reliable when local roughness (γs) was below 10 nm (R² > 0.90).
• Significant dispersion in E values (over 50%) observed even at low roughness (γs = 0).

Conclusions:

• Accurate correlation of elastic modulus (E) with local roughness (γs) is achievable.
• Local roughness significantly impacts nanoscale mechanical property measurements.
• A tip-to-sample contact model explains roughness heterogeneity effects on bone's nanoscale topography.