Browsing by Author "Zioupos, P"
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Item Open Access Changes to the micro-architecture and material properties of the human clavicle and rib in ontogeny(2019-12) McGivern, Hannah L; Zioupos, P; Márquez-Grant, NicholasThe detrimental effects of ageing on the human skeleton are universally resonant. With increase in age, an increased fragility at the macroscopic scale is observed in bone, which is indicative of changes that occur at different levels within the heterogeneous and complex, hierarchical arrangement of this biological composite. In spite of that, a comprehensive understanding of ageing characteristics in the medial clavicle is largely missing from the literature. The seminal research currently available concerns developmental markers such as morphological alterations to shape and structure, which are capped at the point of skeletal maturity. Estimating age-at-death continues to be one of the most challenging responsibilities for forensic anthropologists when compiling a biological profile for unidentified skeletonised human remains (most especially following the maturation of the skeleton). The medial clavicle and sternal rib ends are fundamental to age estimation; the former is the last bone to fuse in the human skeleton making the development ideal for estimating age when the remainder of the skeleton has completed epiphyseal fusion, and the latter are easily accessible during routine autopsy. Current methods which utilise these skeletal sub-regions are primarily qualitative and rely on the expert interpretation of subjective traits which relate to broad and descriptive phase categories. There is a need to go beyond using morphological biomarkers currently employed in forensic anthropology. The introduction of new, quantitative techniques is therefore fundamental to addressing the following unanswered question: what significant, ontogenetic changes occur beyond the macro-scale which can be utilised for generating multivariate age prediction models for the clavicle and rib? In order to address this question, the primary research aim for this research was to characterise statistically significant (p0.7 to effectively predict age-at-death. This novel approach addresses disciplinary norms through the application of micro-computed tomography (µ-CT), nanoindentation and the combined diagnostic power of two thermo-analytical techniques (DSC-TGA) to elucidate agerelated changes in a sample of 161 cadaveric specimens from 58 donors at a scale beyond what has thus far been presented in the literature. Accordingly, a series of associated hypotheses were devised concerning the individual constituent parts, which altogether contribute to the physical manifestiations of age and form the complex arrangment of bone, using each of these techniques. The effect of the size of the sample has also been considered. The age range of the sample in question (12-59 years) focuses on a division of the age spectrum which has received less attention in previous studies, particularly in comparison to study groups which have primarily comprised of elderly individuals. Firstly, a non-destructive assessment of the morphometric characteristics of the trabecular bone located in the medial end of the clavicle was implemented using micro-computed tomography (µ-CT) to test for statistically signficant (p0.7 which is indicative of a strong model. iv Additionally, the value of adopting a multi-method system was illustrated using Principal Component Analysis (PCA) which revealed the extent to which principal components (namely HVIT, EIT, percentage loss of organic weight [Or%] and final percentage weight of mineral phase [Ash%]) were contributing to clustering patterns associated with age. These findings explore the research hypothesis which concerns the identification of changes to clavicle and rib physiology and mechanical behaviour in ontogeny; details that will hold significant value in medico-legal cases for age-atdeath estimation. This research also addresses set objectives concerned with the development of easily reproducible and accurate methods of age-at-death estimation using the medial clavicle and sternal end of the sixth rib without specialist anthropological expertise. The results presented also contribute to basic knowledge of mechano-biology for micro- and nano-structures that influence fracture risk at the organ level, which is of interest to clinicians in orthopaedic biomechanics and is also vital to other sectors. For example, the automotive industry can use such data to establish whether age-related changes to the structure and material composition of these bones lessens the failure threshold and mechanical behaviour of the chest in vehicle collisions. This information in turn could also contribute to the improvememt of automotive safety designs.Item Open Access Whole-body vibration in the defence maritime environment: analysis and simulation of vertebral cancellous bone(2018-06) Shanker, Tobias-Akash; Zioupos, PWhole-body vibration has been shown to increase the risk of low back pain, especially during extreme exposures such as on marine craft which can reach peak loads of 20g during “slamming”. Wedge fractures and trabecular damage of vertebrae have been noted at these high acceleration events. There is a need of a quantitative link between whole-body vibration and spinal damage, with possible tools for prediction. There is currently little known about the role trabecular damage plays under damage from Whole-body vibration, as well as a lack of robust and repeatable trabecular fatigue FE techniques. A fatigue model for trabecular vertebral bone was developed in four steps: Fatigue testing of porcine vertebral cores; validation of a novel element material method; fatigue simulation of a porcine core to select the failure method; prediction using the validated material mapping model with the best failure method on human vertebral cubes. The fatigue tests were carried out on porcine trabecular cores loaded at 2Hz with varying normalised stress values until fatigue failure. Signal analysis was used to examine the vibrational statistics as per ISO 2631-1. This was done to both compare the statistical approaches used in measuring vibration and quantifying a link with in-vivo damage. Vibration Dose Value exposure was found to be the best predictor of failure within these tests. Its 4th order averaging accounted for minute differences in acceleration that RMS could not, even at the low frequency tested. Fatigue of porcine bone has not been extensively examined in the literature and experimental results indicate that there are significant differences in its fatigue behaviour compared to human and bovine bone. Currently there is a need to calibrate the material models used in finite element simulations to achieve parity with experimental testing. This thesis validates a novel greyscale mapping technique which does not require calibration. This was done on human trabecular cores taken at different orientations, with both experimental and finite element simulations. With these tissue material ii properties the simulations showed good agreement in terms of mechanical response in all three directions. Fatigue was calculated using finite element analysis on a porcine core which was validated against experimental results. Three methods were tested for this: A stress based model which bases the element failure criteria in respect to the cycle number; a model which calculates failure by the specific element stress and a strain model which fails elements based upon total element strain. This was conducted using a direct iterative approach using linear isotropic material properties with failure calculated after each cycle, keeping down computational costs. All methods took roughly the same amount of time for a load step. Failure was predicted much sooner in comparison to the experimental with the specific element stress and strain models. The method which varies failure based on cycle count was selected as it was the most accurate. As porcine fatigue testing has not been examined the results were difficult to compare and differed from previous experiments on human and bovine tissues. Using the validated material model and the best performing fatigue method this was then applied to Human trabecular specimens to estimate the fatigue life. The cubes were then loaded in the main physiological direction from in-vivo loading. This predicted most of the expected mechanical behaviour during fatigue including a linear relationship between damage fraction and modulus reduction. It also highlights the importance of angular orientation in regards to trabecular fatigue life. Although it tended to underestimate the fatigue life of bone, it was in good agreement with the literature over the normalised stress range tested. The differences in simulated fatigue behaviour and the literature, seen previously with porcine tissue, were not apparent here. With further study and validation this model has the potential to improve the understanding of trabecular fatigue failure using vibration exposure as the model stimulus