Title:Is it Necessary to Calculate Young’s Modulus in AFM Nanoindentation Experiments Regarding Biological Samples?
Volume: 13
Issue: 1
Author(s): Stylianos-Vasileios Kontomaris*, Anna Malamou and Andreas Stylianou
Affiliation:
- Faculty of Architecture, Engineering & Built Environment, Athens Metropolitan College, Athens,Greece
Keywords:
Mechanical properties, non-homogeneous samples, anisotropic samples, young's modulus, indentation work, nanoscale.
Abstract:
Background: The determination of the mechanical properties of biological samples using
Atomic Force Microscopy (AFM) at the nanoscale is usually performed using basic models arising
from the contact mechanics theory. In particular, the Hertz model is the most frequently used theoretical
tool for data processing. However, the Hertz model requires several assumptions, such as homogeneous
and isotropic samples and indenters with perfectly spherical or conical shapes. As it is widely
known, none of these requirements are 100 % fulfilled for the case of indentation experiments at the
nanoscale. As a result, significant errors arise in the Young’s modulus calculation. At the same time,
an analytical model that could account complexities of soft biomaterials, such as nonlinear behavior,
anisotropy, and heterogeneity, may be far-reaching. In addition, this hypothetical model would be ‘too
difficult’ to be applied in real clinical activities since it would require a very heavy workload and
highly specialized personnel.
Objective: In this paper, a simple solution is provided to the aforementioned dead-end. A new approach
is introduced in order to provide a simple and accurate method for mechanical characterization
at the nanoscale.
Methods: The ratio of the work done by the indenter on the sample of interest to the work done by the
indenter on a reference sample is introduced as a new physical quantity that does not require homogeneous,
isotropic samples or perfect indenters.
Results: The proposed approach provides an accurate solution from not only a physical perspective
but also a simpler solution which does not require activities such as the determination of the cantilever’s
spring constant and the dimensions of the AFM tip.
Conclusion: It has been observed from this opinion paper that the solution aims to provide a significant
opportunity to overcome the existing limitations provided by Hertzian mechanics and apply AFM
techniques in real clinical activities.
