Investigation of age related changes in porcine cortical bone with a focus on reference point indentation

This thesis focuses on reference point indentation (RPI) as a method to determine age related changes in porcine cortical bone. RPI uses a reference probe that sets the zero position for a test probe, which indents samples over a number of cycles. Various polymers and porcine cortical bone have been utilized to further understanding of the RPI technique. The goal of this research is to use this novel equipment to determine differences in mechanical properties of bones, specifically young porcine bones. While RPI is the main technique used in this study, it has been supplemented by techniques such as scanning electron microscopy (SEM), three-point bend tests, nanoindentation, computed tomography (CT) scans, and bone material strength (BMS) measurements made using the Osteoprobe, a clinical indentation device. This thesis is comprised of three separate studies. The first study in this thesis analyzes the RPI testing procedure using six month porcine cortical bone with the intent of developing a standard test procedure. The RPI outputs were analyzed as a function of force magnitude, preconditioning, variation within a sample and between samples, number of cycles, indentation surface (transverse versus longitudinal, polished versus unpolished), and micro-computed tomography radiation exposure. SEM was used as support for the choice of force magnitude. The next study in this thesis is an investigation into the connection between RPI measurements, Osteoprobe measurements and known material properties of nine polymers. Eight 3D printed polymers and a standard polymer included with the RPI test machine were tested using both RPI and the Osteoprobe. These results were then compared to each other as well as the polymers’ known material properties. The final part is the main study of this thesis. In this study, age related changes in porcine cortical bone were analyzed using RPI as well as several other experimental techniques. This study used porcine bones obtained from animals of 0 to 20 weeks of age at four week intervals, resulting in six separate age groups evenly spaced throughout the animal’s early developmental stages. Tests used to determine the age related changes were three-point bend tests, nanoindentation, CT scans, RPI measurements and BMS measurements