Bone Indentation

Motivated by the implications of metabolic bone diseases and their effects on bone fragility, this research investigated the material properties of bone extracellular matrix (ECM). The experimental method of indentation at the micrometer or nanometer scale represents a powerful method to quantify elastic and post-yield material properties with a high spatial resolution and in various directions. On the experimental side, efforts were directed towards standardization of sample preparation, establishment of continuous stiffness measurements and testing under wet physiological conditions. On the computational side, a phenomenological constitutive model for bone ECM including the simultaneous viscous flow of plastic strain and reduction in elastic modulus was developed. A generalized yield criterion was formulated to cover a broad range of plastic and damage behavior and open the perspective of an inverse method to identify the post-yield properties of bone with a virtual indentation using finite element analysis. For this purpose, an existing mesh was improved and validated to model a conical or spherical tip indenting bone tissue along axial and transverse orientations with typical depths selected in the experiments.