Structure-property relations of porcine trabecular bone and micro-CT imaging of various materials

This thesis addresses the characterization of materials with a focus on trabecular bone. In the first part, we aim to find relations between morphological measures of trabecular bone and its Young’s modulus and ultimate compressive strength. Previous research has showed that apparent density and porosity are the main factors that influence mechanical properties of trabecular bone. However, due to the complex structure of trabecular bone, additional parameters may be needed to accurately predict trabecular bone’s properties. Thus, we measure the apparent density, mineral content, trabecular orientation, trabecular thickness, fractal dimension, surface area and connectivity of the 6 month porcine trabecular bone using micro-computed tomography (micro-CT) and investigate how they influence Young’s modulus and strength measured using uniaxial compression test. To further investigate the effect of mineral density on mechanical properties of bone, a separate experiment was conducted on bovine trabecular bone. Demineralized bovine bone samples show a dramatic decrease in mechanical properties indicating the importance of mineral density. Effects of preservation (fresh, and 1 and 5 year freeze durations) and micro-CT radiation are also investigated. Cylindrical porcine specimens were made from femoral head and divided into three groups depending on the freezing period. We conclude, using multiple regression, that porosity and apparent density are the major factors that contribute to the ultimate strength but other parameters also contribute and combined provide a more accurate prediction of bone strength. We also find that long term freezing influences mechanical properties of bone. Bones which were not frozen have higher Young’s modulus and ultimate stress than the bones which were frozen for a long period of time. Also, the influence of porosity and apparent density on the mechanical properties is more dominant for fresh bone. Furthermore, the structure-property relations for long-term frozen trabecular bone are more complex. In the second part, various materials were scanned using a high resolution micro-CT. Micro-CT is an effective imaging modality utilized in many research areas. Taking advantage of this tool, parameters such as porosity, mineral content and perimeter were measured without destroying the materials. These materials are frog tarsus bone, thermoplastic fiber reinforced composites, and metal-carbon materials called covetics, all from collaborative projects. The mineral content of frog bones agrees well with measurements in literature. For thermoplastic composites, with randomly arranged long fibers, the fiber orientation measurements obtained using micro-CT is more accurate than using the optical imaging analysis method. Porosity of metal-carbone materials called covetics was also measured. In short, we used the micro-CT to characterize porosity and microarchitectures of biological materials such as bone, polymer matrix composites and metal-based materials