Characterization of developing porcine cortical bone: applications of mechanical and optical methods

This thesis focuses on the characterization of developing pig bone under the effects of age-related changes and nutritional disease using several methods of characterization. The main characterization techniques are as follows: reference point indentation (RPI), compression testing, quantitative backscattered electron (QBSE) imaging, and nanoscale dynamic mechanical analysis (nanoDMA). The eventual goal of using this diverse set of characterization techniques is to understand and catalogue the changes that occur in bone due to biological factors. By understanding the various characteristics of bone, i.e. mineralization levels, property variations between quadrants, effects of disease, and microstructure variations, one can predict properties based on diagnostic knowledge. The first study of this thesis is a partial review of the state of reference point indentation of bone. The origin of the device is explored, along with studies devoted to developing ideal operating conditions. Studies focusing on modeling RPI are also examined. Along with this literature review, an analysis of tip wear of the BioDent and Osteoprobe devices is presented. The second study is a characterization of the mechanical effects on bone caused by induced colitis using three different measurement techniques. First, reference point indentation using the BioDent device was performed on femora and tibiae on both healthy and induced-colitis samples. Compression tests were completed on milled samples taken from cortical bones of left femora to determine modulus of elasticity and ultimate compressive strength. Finally, bone samples were dried and ashed to determine porosity and bulk mineral volume. The next study is a demonstration of the quantitative backscattered electron imaging technique (QBEI). This technique is applied to characterize the effect of age in developing bones on the hydroxyapatite mineralization percentage. The sample preparation technique and data analysis procedure are demonstrated for a general desired compound. The final study of this thesis is an investigation using nanoindentation of the viscoelastic properties of the outer layer of bone, known as the periosteal bone, compared to the inner, or endosteal, tissue. NanoDMA was used to capture hardness, complex modulus, and tan-delta data at a distribution of frequencies from 10-200 Hz. Determining the difference in properties between periosteal and endosteal bone is crucial in understanding measurements taken by reference point indentation devices