Human cancellous bone mechanical properties and penetrator geometry in nanoindentation tests.

PURPOSE: The goal of the study was to determine the influence of the penetrator geometry on the human cancellous bone mechanical properties in indentation tests. The aim of this research was also the assessment of the material properties of bone structures, having in mind the energy aspects of the curve obtained in the cycle: inelastic loading and elastic unloading. METHODS: The samples were resected from a femoral heads of patients qualified for a hip replacement surgery. During the Depth Sensing Indentation tests, hardness and elastic modulus of the cancellous bone tissue were measured using the spherical and Vickers penetrators. Measurements were made in a node and in a trabecula for each sample. RESULTS: The analysis of the measurement results and the calculations of total energy, i.e., elastic and inelastic, and those of the parameters of hardness and elasticity made it possible to assess the influence of the penetrator geometry on the mechanical properties of bone structures at a microscopic level. CONCLUSIONS: It was found, with respect to the methodology of indenta- tion, that without determining the shape of the penetrator and the site of the indentation, an objective assessment of the micro mechanical properties of the tested material is not possible.

Mechanical properties of cancellous tissue in compression test and nanoindentation.

The goal of the study was to determine material constants of cancellous tissue in a compression test taking into account stress-strain characteristics. The nineteen test samples were resected from a femoral head of a patient qualified for a hip replacement surgery. During the compression tests, load-displacement curves were evaluated and stress-strain characteristics (𝜎-𝜀) of the cancellous bone tissue were calculated. A special one-touch extensometer was used. The use of an extensometer improves the displacement measurement accuracy with respect to the measurement using standard crosshead. The obtained values of the mechanical parameters as well as the stress-strain curves are the basis for further research going into the development of bone tissue constitutive equations.

The influence of the cumulated deformation energy in the measurement by the DSI method on the selected mechanical properties of bone tissues.

PURPOSE: The goal of the study was to determine the influence of DSI test conditions, i.e., loading/unloading rates, hold time, and the value of the maximum loading force on selected mechanical properties of trabecular bone tissue. METHODS: The test samples were resected from a femoral head of a patient qualified for a hip replacement surgery. During the DSI tests hardness (HV, HM, HIT) and elastic modulus (EIT) of trabecular bone tissue were measured using the Micro Hardness Tester (MHT, CSEM). RESULTS: The analysis of the results of measurements and the calculations of total energy, i.e., elastic and inelastic (Wtotal, Welastic, Winelastic) and those of hardness and elasticity made it possible to assess the impact of the process parameters (loading velocity, force and hold time) on mechanical properties of bone structures at a microscopic level. CONCLUSIONS: The coefficient k dependent on the EIT/HIT ratio and on the stored energy (ΔW = Wtotal - Welastic) is a measure of the material reaction to the loading and the deformation of tissue.