Site-Specific Evaluation of Bone Mechanical Properties Using 3D-Printed Artificial Bone Microstructures

Abstract

This thesis examines the feasibility of using highly nonlinear solitary waves (HNSW) for nondestructive evaluation (NDE) of the effective elastic modulus of trabecular bone. The proposed method holds promise as a reliable method for testing bone quality, as it can offer an assessment based on the effective elastic modulus of bone rather than only the bone mineral density offered by the conventional clinical DEXA scans. A bone microstructure reconstruction scheme is used to create digital twins of human trabecular bone for three regions of interest within the femur (femoral head, femoral neck, intertrochanteric region). These digital twins are used to 3D print artificial bone microstructure samples, which are then examined using HNSWs propagating in a granular chain of steel beads. In the experiments, the granular chain interacts with the porous bone sample through a flat-ended bead which ensures that the bone microstructure is in a state of uniform compression during the test. This thesis investigates the dynamic interaction between HNSWs and the 3D printed bone, as well as artificial bone in the form of polyurethane (PU) foam of varying densities, and how the features of the reflected nonlinear pulses relate to the bone’s elastic modulus obtained from standardized compression tests. Moreover, a novel discrete element model (DEM) able to predict the dynamic interaction between the HNSWs and the test media was developed to establish a relationship between reflected solitary wave features and the effective elastic modulus of the inspected bone sample. This model was validated by a hybrid DE/FE model and through experimental observations, providing insights into how bone size variations affect wave interaction. While the DEM effectively replicated general trends in the features of the reflected waves, it revealed discrepancies in time delays of the emergence of the reflected waves when compared with experimental observations, suggesting that the dynamic test conditions might reflect a stiffer material response due to the elevated strain rate in the experiments, a factor not yet integrated into the model. Future research is needed to develop models that can account for the viscoelastic properties of the artificial bone material and the effects of strain rate on the predicted elastic modulus.

Date of Award	7 May 2024
Original language	American English
Supervisor	Andreas Schiffer (Supervisor)