This thesis describes the development of artificial disc technology for the replacement of intervertebral discs in the human lumbar spine. The clinical problem is back pain. There may be a relationship between certain forms of back pain and disc degeneration. The mechanical properties of human intervertebral discs are examined in detail. The genetic basis of disc degeneration is presented. The hypothesis is that such degeneration leads to a loss of normal stiffness in the segments affected leading to abnormal mechanical behaviour which in turn leads to pain. The evidence for this is presented. The development of surgical solutions to relieve back pain, from fusion through first generation mechanical artificial discs to elastomeric designs, is traced. The author‘s personal contributions to this area of knowledge are set out. The appreciation of the requirement for a restoration of physiological stiffness is argued throughout, showing where fusion and first generation discs have not met the clinical aim of pain relief, because they have not restored physiological stiffness. The path to an elastomeric, viscoelastic, polyhydrocarbon, rubber solution in the form of the “Freedom“ disc has filled 17 years of the author‘s academic pursuits. It will be shown that this technology may represent a possible solution to the clinical problem. Failure is part of all new advancement and this too is presented, to show how that has influenced thinking, producing original ideas to overcome these failures. Providing lessons are learned from these failures then our patients in the future will benefit.

The study of dynamics and performance of flying discs is motivated by how variations in their design features influence the aerodynamic characteristics and flight performance, particularly range. Reviews in the literature focus on the development of fundamental research in flying discs and on the performance of sports projectiles. Theoretical background on disc dynamics, range and sensitivity are given. This work investigates disc aerodynamics by performing wind tunnel experiments to measure aerodynamic loads on a set of generic parametric discs and a set of commercial golf discs. The parametric discs isolate various geometrical features such as thicknesses, cavities, leading edge curvatures and cambers to study the influence of these parameters on aerodynamic characteristics. The commercial golf discs consist of three different categories known as putter, mid-range and driver: these discs are used for short, medium and long flight range, respectively. To study the performance, aerodynamic data of the golf discs are used as inputs in numerical simulations to predict their flight trajectories and range. Effects of launch attitude on range are assessed to study the optimal initial launch conditions to achieve maximum range. Further, the simulation provides a direct approach to analyse range sensitivity on launch parameters. Results from the experiments show a number of significant findings on disc geometry. First, a cavity is fundamentally important for a disc to have satisfactory flying qualities: the presence of the cavity produces a significant aft shift in the aerodynamic position to minimize the pitching moment about the centre of the disc. Hence, the disc will have a minimal tendency to roll about the flight axis. Second, the thickness of a disc has a significant effect on its profile drag: increasing the thickness increases the profile drag. Third, a disc with a positive camber produces a relatively higher lift-to-drag ratio (CL/CD) compared to one with no camber. Fourth, the effect of tapering a flat leading or trailing edge of a disc leads to a reduction in its lift (within the angles of attack tested in the study) with a significant reduction in its drag. Fifth, it is shown that peak lift-to-drag ratio of a free flying disc is not necessarily a good indicator of performance because the angle of attack (and hence, lift-to-drag ratio) varies widely through a typical flight. Furthermore, a disc with a significant pitching moment will roll significantly about the flight path direction, further reducing the achievable range for a given lift or drag characteristic. Finally, a novel method to quantify disc sensitivity with respect to changes in launch conditions has been developed. The simulations show that the range sensitivity of each disc with respect to launch pitch angle varies significantly, with discs design for long range being much more sensitive (and therefore harder to throw accurately) than discs designed for short range.

This Paper deals with a design of tribometer for pin-on-disc and disc-on-disc tests. The purpose of these tests is Investigation of friction coefficient during hot forming. The main emphases of this paper are tool heating and quick tool change. The conductive sample heating is analyzed with FEM software Ansys and the results of this snalysis are taken into design consideration. Existing pin mounting design is considered as satisfying. Various disc mounting concepts are compared. The best solution - specimen mounting by an inside clamping cone with integrated specimen ejector was manufactured (heating excluding) and successfully tested.

Introduction: A computer-based classification system is proposed for the characterization of cervical intervertebral disc degeneration from saggital magnetic resonance images. Materials and methods: Cervical intervertebral discs from saggital magnetic resonance images where assessed by an experienced orthopaedist as normal or degenerated (narrowed) employing Matsumoto’s classification scheme. The digital images where enhanced and the intervertebral discs which comprised the regions of interest were segmented. First and second order statistics textural features extracted from thirty-four discs (16 normal and 16 degenerated) were used in order to design and test the classification system. In addition textural features were calculated employing Laws TEM images. The existence of statistically significant differences between the textural features values that were generated from normal and degenerated discs was verified employing the Student’s paired t-test. A subset with the most discriminating features (p<0.01) was selected and the Exhaustive Search and Leave-One-Out methods were used to find the best features combination and validate the classification accuracy of the system. The proposed system used the Least Squares Minimum Distance Classifier in combination with four textural features with comprised the best features combination in order to classify the discs as normal or degenerated. Results: The overall classification accuracy was 93.8% misdiagnosing 2 discs. In addition the system’s sensitivity in detecting a narrow disc was 93.8% and its specificity was also 93.8%. Conclusion: Further investigation and the use of a larger sample for validation could make the proposed system a trustworthy and useful tool to the physicians for the evaluation of degenerative disc disease in the cervical spine. / Σκοπός: Η στένωση των μεσοσπονδύλιων δίσκων της αυχενικής μοίρας, ως κύρια έκφραση εκφυλιστικής νόσου, είναι μια από τις σημαντικότερες αιτίες πρόκλησης πόνου στην περιοχή του αυχένα. Στην κλινική πράξη η αξιολόγηση της στένωσης γίνεται μέσω μέτρησης του μεσοσπονδύλιου διαστήματος, σε διάφορες απεικονίσεις της αυχενικής μοίρας του ασθενούς. Στην παρούσα εργασία προτείνεται μια υπολογιστική μέθοδος ανάλυσης εικόνας, για την αυτοματοποιημένη εκτίμηση της στένωσης από εικόνες μαγνητικής τομογραφίας. Υλικό και Μέθοδος: Μελετήθηκαν 34 μεσοσπονδύλιοι δίσκοι από οβελιαίες τομές μαγνητικής τομογραφίας της αυχενικής μοίρας, οι οποίες ελήφθησαν με χρήση Τ2 ακολουθίας. Η στένωση των μεσοσπονδύλιων δίσκων αξιολογήθηκε από έμπειρο ορθοπαιδικό βάσει της κλίμακας Matsumoto. Οι δίσκοι χωρίστηκαν σε δύο κατηγορίες: (α) 16 φυσιολογικοί και (β) 16 δίσκοι που παρουσίαζαν στένωση. Με χρήση διαδραστικού περιβάλλοντος επεξεργασίας εικάνας καθορίστηκε το περίγραμμα των μεσοσπονδύλιων δίσκων οι οποίοι αποτελούν τις προς ανάλυση περιοχές ενδιαφέροντος (Π.Ε.). Σε κάθε Π.Ε. εφαρμόστηκαν αλγόριθμοι εξαγωγής χαρακτηριστικών υφής. Συγκεκριμένα υπολογίστικαν χαρακτηριστικά υφής από στατιστικά πρώτης και δεύτερης τάξης καθώς και χαρακτηριστικά από τα μέτρα ενέργειας υφλης κατλα Laws. Τα παραπάνω χαρακτηριστικά, ποσοτικοποιούν διαγνωστικές πληροφορίες της έντασης του σήματος της Π.Ε. και συσχετίζονται με τη βιοχημική σύσταση των απεικονιζόμενων δομών. Τα εξαχθέντα χαρακτηριστικά υφής αξιοποιήθηκαν για τη σχεδίαση του ταξινομητή ελάχιστης απόστασης ελαχίστων τετραγώνων, ο οποίος χρησιμοποιήθηκε για το διαχωρισμό μεταξύ φυσιολογικών δίσκων και δίσκων που παρουσίαζαν στένωση (εκφυλισμένων). Αποτελέσματα: Η ακρίβεια της ταξινόμησης φυσιολογικών και εκφυλισμένων μεσοσπονδύλιων δίσκων ανήλθε σε 93.8%. Η ευαισθησία καθώς και η ειδικότητα της μεθόδου, σε ότι αφορά την ανίχνευση εκφυλισμένων δίσκων, είναι επίσης 93.8%. Συμπέρασμα: Με δεδομένο το μικρό μέγεθος του δείγματος που χρησιμοποιήθηκε για το σχεδιασμό της μεθόδου, απαιτούνται περετέρω εργασίες πιστοποίησης της ακρίβειας ταξινόμησης, προκειμένου η μέθοδος αυτή να αξιοποιηθεί από ακτινολόγους και ορθοπαιδικους, ως βοηθητικό διαγνωστικό εργαλείο.

Esta tese estuda a emissão de ruído de alta frequência em freios automotivos, conhecida como squeal. Para tanto, uma série de ensaios foram executados em sistemas de freio em um dinamômetro inercial. Foram colocados acelerômetros na pastilha e no caliper em três direções ortogonais, e foram testados dois diferentes tipos de sistemas de freio comerciais. Os ensaios revelaram que, durante os períodos silenciosos, o movimento vibratório da pastilha acontece tanto na direção tangencial radial quanto na direção radial no plano definido pelo disco, além da direção axial. Estas vibrações ocorrem de modo independente, não mostrando acoplamento entre os movimentos. Durante os períodos de emissão sonora intensa, os valores de vibração aumentam significativamente e ocorre o acoplamento dos movimentos nas direções tangencial e radial, que passam a apresentar sincronismo de fase e de frequência. O movimento da pastilha na direção radial é explicado pelos modos de vibração do disco, e pastilha e disco são tratados como dois osciladores fracamente acoplados. Para o tratamento de osciladores, utiliza-se o modelo de Kuramoto. O sincronismo, neste modelo, ocorre devido ao acoplamento entre os osciladores e devido à proximidade das frequências naturais de pastilha e disco. A aplicação do modelo nos sistemas ensaiados mostrou boa aderência aos dados experimentais. Finalmente, é proposta a utilização de um coeficiente adimensional de maneira a incluir no estudo dinâmico do sistema variáveis puramente tribológicas. / This paper studies friction induced high frequency noise in automotive brakes, known as squeal. Aiming this purpose, a series of experiments were performed using brake systems in an inertial dynamometer. Accelerometers were installed on pad and caliper, measuring in three orthogonal directions, in two different commercial brake systems. The tests showed that, during the silent runs, pad vibration happens in tangential and radial directions, besides the axial direction, considering the coordinate reference frame on the plane defined by the brake disc. These vibrations happen in an independent fashion, indicating no coupling between motions in different directions. During the squeal periods, however, vibration amplitudes increase sharply and phase and frequency synchronization between tangential and radial vibrations is observed, indicating vibration coupling. Pad movement in radial direction is caused by disc in-phase vibration mode. Pad and disc are treated as two harmonic oscillators according to Kuramoto model. In this model, synchronization is caused by weak coupling between pad and disc natural frequencies, due to frequency proximity. A numerical simulation of Kuramoto model was able to emulate the experimental data. Finally, a new non-dimensional coefficient is proposed in order to include in this dynamic model the influence of pure tribological effects.

This thesis reports the design and development of novel voltammetric pH sensors for buffered, low-buffered and unbuffered media. pH sensors in stagnant and hydrodynamic environments were designed and developed for performing measurements using square wave voltammetry. Chapter 1 introduces the motivation of this project, the current development of electrochemical sensors, and the basic theory and techniques of electrochemistry concerned within the thesis. The existing development of carbon-based electrochemical sensors and the application of screen-printing technology in sensor fabrication are highlighted. Chapter 2 introduces the screen-printing technology and the fundamental methods of numerical simulation. In addition, reagents, equipment and software packages used in the thesis are listed in this chapter. In Chapter 3, a novel design of quinone derivative-based pH probes is presented for the application in stagnant weakly buffered media (< 1mM), based on previous studies of quinone compounds in buffered media. The results from the weakly buffered system is consistent with the results in buffered systems. To further extend the application of this design in unbuffered media, a numerical model of a pH-sensitive redox particle immobilised on an electrode was developed, which predicted that the accumulation of hydrogen ions near the electrode is the possible limiting factor for the performance of this design in unbuffered media. To develop a pH-monitoring technology for unbuffered media, Chapter 4 reports on the design, fabrication and testing of different electropolymerised-phenol derivative modified electrodes, which overcome the limitation of hydrogen ions accumulation. The results revealed that 2-(methylthio)phenol graphite resin electrodes have high accuracy (ca. 1% error) in unbuffered media, benchmarked by a commercial glass pH meter. This is the first detailed study on the v application of the economical and scalable technology in pH sensing in unbuffered environment. Chapter 5 presents a unique design of electrochemical pH sensors, free from the need to use a glass reference electrode. This design integrates a pH indicator and an internal reference electrode. Different designs of ferrocene screen-printed electrodes were tested as the internal reference electrode. The nafion-coated ferrocene screen-printed electrode showed stable peak potential in a wide pH range (pH 1 - 12) with good durability (stable in 500+ cycles of test). It was then cross connected with an alizarin electrode, forming the pH sensor free from a glass reference electrode. Chapter 6 describes novel designs of hydrodynamic pH sensors. The design of a microfluidic pH sensor modified by poly-sodium salicylate was firstly demonstrated. The sensor showed a Nernstian response in a wide pH range and, in hydrodynamic conditions, provided improved accuracy in unbuffered media compared to the stagnant state. For more convenient measurements, a novel rocking disc electrode was studied for pH sensing, modified with alizarin and poly-salicylic acid as pH indicators. The electrodes modified by both chemicals showed a Nernstian response in buffered media and the highest accuracy in unbuffered media was reached at 50 rpm.

Back pain is the second most common neurological ailment in the United States and the leading cause of pain and disability. More than 80% of the total US population experiences back-pain during their life time and the annual back pain related healthcare costs exceed 100 billion dollars. While the exact cause of low back pain (LBP) is still unknown, degeneration of the intervertebral disc (IVD) has been suggested as a primary contributor. IVD is the largest avascular tissue in the human body and it is composed of three integrated tissues (annulus fibrosus - AF, nucleus pulposus - NP and cartilaginous end plate - CEP). IVD functions as a shock-absorber during motion and provides flexibility to motion of the spine. Maintaining IVD tissue integrity is an energy demanding process. Studies have shown that mechanical loading affects cellular biosynthesis of IVD tissue and may also promote IVD degeneration. However the path to this effect is still unknown. We propose a link between mechanical loading and cell energy production which contributes to altered cellular biosynthesis. Thus, we investigated the effects of mechanical loading on IVD cell energy metabolism under various mechanical loading regimes. Porcine AF and NP cells were isolated and seeded in 2% agarose at a 5,000,000 cells/mL cell density. A custom made bioreactor was used to conduct compression experiments. The experiment groups were: 15% static compression; 30% static compression; 0.1, 1 and 2 Hz dynamic compression at 15% strain magnitude. Experiment duration was 4 hr. ATP concentration in cell-agarose construct and culture media were measured using Luciferin-luciferase method to evaluate ATP production and ATP release from cells respectively. Lactate concentration in media was measured using lactate dehydrogenase enzymatic assay. Nitrite (stable metabolite of nitric oxide - NO) concentration in media was measured by Greiss Assay. DNA content per sample was measured using fluorometric assay. DNA content per sample was used as an internal control; all compressed samples were then normalized to unstrained control group. ATP production of AF cells was up regulated by static and dynamic mechanical loading. Data suggests that AF cell response to mechanical loading is primarily loading amplitude dependent. NP cells exhibited an increased ATP production at 1 Hz dynamic loading but remained comparable to control samples at other tested conditions. AF cells produced an increase in NO production at 1-, 2 Hz dynamic loading. NO production of NP cells was up regulated by mechanical loading at all tested conditions. ATP release was up regulated at higher frequencies in AF cells. In addition to higher frequencies (1 Hz and 2 Hz) NP cell ATP release was also up regulated by 30% static compression. Thus, this study clearly illustrates that mechanical loading affects IVD cell energy production.

Low back pain is highly prevalent in the developed world, with 80% of the population being affected at some point in their lives. Herniation, a common injury to the intervertebral disc, is characterized as the posterior migration of the nucleus pulposus through the layers of the annulus fibrosus. Various risk factors have been associated with the development of disc herniation, but the mechanisms are largely not understood. For example, exposure to vibration has been linked to the occurrence of herniation, yet our understanding of this association is not clear. It is hypothesized that vibration cyclically loads the tissues of the intervertebral disc until failure occurs as a result of fatigue. Tissues at risk of fatigue failure may include the intra-lamellar matrix, the connective tissue found between collagen fibres within a single lamella, and the inter-lamellar matrix, the connective tissue found between adjacent lamellae. In order to determine the mechanistic link between vibration and herniation, a firm understanding of the properties of the intervertebral disc as well as the intra and inter-lamellar matrices are of utmost importance. Further, it is important to determine these properties under physiological loading scenarios. This thesis consists of five studies, which have each provided a unique piece to the intervertebral disc herniation puzzle in order to better understand this mechanistic link. First, it was discovered that annular tissue is subject to significantly higher stresses and is stiffer under biaxial strain as compared to uniaxial strain. Biaxial strain is more representative of the in vivo loading scenario and provides more accurate information regarding scenarios that the annulus can tolerate and those that can result in injury. It was also revealed that, when strained at physiological strain rates (up to 4%/sec), these mechanical properties do not change such that they are independent of strain rate. Therefore, when strained at varying rates akin to voluntary movement, the annulus is not subject to higher stresses or altered stiffness. Second, the effect of vibration, an acknowledged risk factor for herniation, was examined on the mechanical properties of the intra and inter-lamellar matrices. It was discovered that vibration altered these matrices such that they were more extensible and strained to greater magnitudes, yet did not reach higher stresses before failing. It was hypothesized that this increased extensibility was due to damage to elastin, as elastin assists in minimizing tissue deformation and helps tissues recover from tensile strain. The final study assessed the effect of exposure to vibration on the development of disc herniation. The initiation of herniation was observed in a significantly greater number of intervertebral discs exposed to vibration as compared to a control condition. Although epidemiological studies had documented a correlation between exposure to vibration and herniation, this was the first study to conclude that exposure to vibration is in fact a mechanical risk factor for the development of herniation and increases the incidence of herniation. Further, based on the findings of the mechanical properties of the intra and inter-lamellar matrices, and in particular the observed 15-20 times greater failure strength of the intra as compared to inter-lamellar matrix, it would appear that the inter-lamellar matrix, and thus delamination, may be the weakest link in the herniation pathway. This thesis has uncovered new information regarding physiological mechanical properties of the annulus. Further, new information regarding the intra and inter-lamellar matrices was obtained, improving our understanding of the healthy disc. Last, by subjecting the disc to a known risk factor for herniation, hypotheses were generated regarding the initiation and progression of disc herniation, specifically related to the roles of the intra and inter-lamellar matrices.

Low back pain is highly prevalent in the developed world, with 80% of the population being affected at some point in their lives. Herniation, a common injury to the intervertebral disc, is characterized as the posterior migration of the nucleus pulposus through the layers of the annulus fibrosus. Various risk factors have been associated with the development of disc herniation, but the mechanisms are largely not understood. For example, exposure to vibration has been linked to the occurrence of herniation, yet our understanding of this association is not clear. It is hypothesized that vibration cyclically loads the tissues of the intervertebral disc until failure occurs as a result of fatigue. Tissues at risk of fatigue failure may include the intra-lamellar matrix, the connective tissue found between collagen fibres within a single lamella, and the inter-lamellar matrix, the connective tissue found between adjacent lamellae. In order to determine the mechanistic link between vibration and herniation, a firm understanding of the properties of the intervertebral disc as well as the intra and inter-lamellar matrices are of utmost importance. Further, it is important to determine these properties under physiological loading scenarios. This thesis consists of five studies, which have each provided a unique piece to the intervertebral disc herniation puzzle in order to better understand this mechanistic link. First, it was discovered that annular tissue is subject to significantly higher stresses and is stiffer under biaxial strain as compared to uniaxial strain. Biaxial strain is more representative of the in vivo loading scenario and provides more accurate information regarding scenarios that the annulus can tolerate and those that can result in injury. It was also revealed that, when strained at physiological strain rates (up to 4%/sec), these mechanical properties do not change such that they are independent of strain rate. Therefore, when strained at varying rates akin to voluntary movement, the annulus is not subject to higher stresses or altered stiffness. Second, the effect of vibration, an acknowledged risk factor for herniation, was examined on the mechanical properties of the intra and inter-lamellar matrices. It was discovered that vibration altered these matrices such that they were more extensible and strained to greater magnitudes, yet did not reach higher stresses before failing. It was hypothesized that this increased extensibility was due to damage to elastin, as elastin assists in minimizing tissue deformation and helps tissues recover from tensile strain. The final study assessed the effect of exposure to vibration on the development of disc herniation. The initiation of herniation was observed in a significantly greater number of intervertebral discs exposed to vibration as compared to a control condition. Although epidemiological studies had documented a correlation between exposure to vibration and herniation, this was the first study to conclude that exposure to vibration is in fact a mechanical risk factor for the development of herniation and increases the incidence of herniation. Further, based on the findings of the mechanical properties of the intra and inter-lamellar matrices, and in particular the observed 15-20 times greater failure strength of the intra as compared to inter-lamellar matrix, it would appear that the inter-lamellar matrix, and thus delamination, may be the weakest link in the herniation pathway. This thesis has uncovered new information regarding physiological mechanical properties of the annulus. Further, new information regarding the intra and inter-lamellar matrices was obtained, improving our understanding of the healthy disc. Last, by subjecting the disc to a known risk factor for herniation, hypotheses were generated regarding the initiation and progression of disc herniation, specifically related to the roles of the intra and inter-lamellar matrices.

The main purpose of this study is to simulate and analyze the temperature and contact pressure of the disc brake plate of a motorcycle during braking by the finite element method. By utilizing the software package Mentate and Marc which are signified with drawing and construction of the brake model to do the analysis of thermal and contact problem. In accordance with the result of analysis, the researcher discussed and compared the three-dimensional model and the two dimensional axial symmetrical model for the temperature, pressure and stress distribution of the brake. Finally, the researcher made some suggestions for the improvement of the mechanism of disc brake plate of a motorcycle.