The management of significant bone defects, delayed and non-union of fractures can be extremely challenging. Development of specific treatment is hindered by an absence of information regarding the molecular events which regulate these processes. In this thesis, a bilateral cancellous bone defect model of the femur and tibia was developed in a rodent and the spatiotemporal profile of TGF-β, BMP 2 and 7, Smads 1, 4 and 5 characterised. Next, the capability of acid solution to augment healing was tested in both a bone defect and in a closed femoral fracture model. Finally, a long term oestrogen deficiency (OVX) rat model of postmenopausal osteoporosis was characterised and the spatiotemporal profiles of IGF-1, IGFR-1, MMP-1, MMP-3, MMP-9, MMP-13, TIMP-1, TIMP-2, BMP-2, BMP-4, BMP-7, TGF-β, Smad4, Smad7, VEGF, Flt-1, Ihh and FGF-2 were compared in femoral osteotomies between OVX and Sham groups. The bilateral cancellous defect model was successfully created with a number of advantages with which to recommend its use in future studies. TGF-β, BMP 2 and 7, Smads 1, 4 and 5 had characteristic spatiotemporal profiles during cancellous bone defect healing suggesting that they have a regulatory role. The results of the acid study were inconclusive and problems with substance delivery and maintenance at the desired site need to be addressed in the future to fully test this hypothesis. No significant differences were detected on histology or three-point mechanical testing between the fracture calluses of acid and control groups. In the final study, OVX rats after six months had significantly increased weight and decreased bone mineral density compared to their sham counterparts. A histological delay in osteotomy healing was observed in the OVX group but no significant differences on tensile testing were seen between OVX and Sham groups up to six weeks. Immunohistochemistry revealed that delayed healing may be due to the down-regulation of IGF-1, BMP-2, 4, and 7 and the up-regulation of MMP-3 in OVX compared to Sham groups. In conclusion, the results of this thesis give some insight into the molecular biology of bone defects and osteoporotic fractures. This information may also be useful in the development of specific treatments aimed at augmenting healing in bone defects and osteoporotic fractures.

Artificial surfaces are increasingly more common in a number of sports including football, rugby and hockey. Each specific sport has mechanical properties designed to suit the requirements of the sport which can be achieved through appropriate selection of surface specification, as well as the appropriate selection of footwear. In player-surface interactions, traction is a key system property that needs to be measured for comfort, performance and any potential injury risk. Many of the current industry tests used to measure traction are simplistic and have limitations when used in tests. The aim of the thesis was to make a contribution to knowledge with regard to the mobilisation of traction and apply this to the understanding of shoe-surface interactions. This was achieved by completing a number of objectives. These included reviewing current knowledge of player-surface interaction behaviour in relation to traction and obtaining relevant human boundary conditions for biofidelic mechanical test development. The mechanisms of traction were then investigated and the variables in the mobilisation of traction identified. The traction forces developed were quantified with appropriate measurement systems. Mechanical test equipment was then developed along with protocols to replicate the translational and rotational lower limb behaviour during sport specific behaviour. This included the standard FIFA rotational device being modified to include two sensors which record continuous data throughout a trial to allow for more than a peak torque value to be analysed. In addition, a piece of equipment to measure translational traction was developed and constructed to support the rotational traction device and help to understand the mobilisation of traction. The device pulled a tray containing a surface sample, with a shoe/plate placed on the sample. The horizontal force was measured, as well as the amount of stud penetration into the surface. It was also necessary to characterise the state of the surface and the effects that any changes may have on the traction that is mobilised. Testing completed involved repeated testing on both the rotational and translational to allow for comparison. Changes in the surface properties were made such as the number of fibres in a set area and the rubber infill density as well as shoe properties such as stud spacing, stud type and number of studs. In the results, the initial stiffness response of the surface was often focussed on as it was stated that this may be a better indicator of the mechanisms involved in the traction mobilised by subjects, compared to peak torque. This is due to actual foot rotation measured in subject testing being observed to be much smaller than the rotation/distance required to produce the peak force. The larger angles/displacements were also considered to help inform the mechanisms of traction. The final objective was to refine the mechanisms based on the experimental design. This all adds to the contribution of knowledge regarding the mobilisation of traction. A key outcome from the thesis is the effect the surface and shoe properties have on traction, therefore it is essential to state the specification when reporting results otherwise comparisons are not able to be made. The mechanism of traction has not previously been fully understood, with this thesis beginning to understand the details of how the change in surface or shoe properties affect how the surface reacts during shoe-surface interactions.

High-performance fibres such as carbon, glass and kevlar are very promising for aerospace applications because of their high strength, stiffness, impact damage and excellent fatigue life. The high cost of the prepreg materials such as pre-impregnated fibre tape/tow and fabrics, and limitations of existing manufacturing processes are a big challenge for the aerospace industry to meet increasing performance demands. Their benefits can only be achieved by using low cost materials and manufacturing methods. In the past three or four decades, there have been substantial technological developments, which are governed by the new materials and their associated manufacturing techniques. The production of carbon fibre is slow and capital intensive, therefore, carbon manufactures produce higher tow counts (number of filaments) to increase production through-put in order to reduce its cost. In other words, 12k carbon tow is much cheaper than 6k or 3k carbon tow. In many applications finer tows are desirable. In this thesis, a fully automated laser feedback tow splitting line has been developed to split higher tow counts (12k spool) into smaller tow counts (split into 6k spools) in order to produce low cost material. The quality of the split tows has been evaluated by recording the data online during the splitting process. The recorded data was later analysed by statistical tools. A four axis modular gantry robotic system has been developed at the University of Manchester in order to deposit dry fibres in a completely flexible manner. To facilitate robotic preforming, an end-effector and mould have been designed and developed in this research. The tow placement program was written in the CoDeSys software which is then uploaded into the motion controller to perform specific motions. The cross-ply laminates have been manufactured by the proposed robotic system using split 6k (produced by the tow splitting process) and original 12k carbon tows. Mechanical test of both composites (12k and split 6k) are presented. A tufting process has been developed and conducted by the robotic system in order to manufacture 3D preforms. The tufted composite was compared with 3D woven and stitched 2D broadcloth in terms of the tensile and interlaminar shear strength properties. X-ray tomography has been conducted to investigate preform geometrical variations of manufactured composites. In addition, preforming cost models have been developed for robotic fibre placement and 3D weaving.

Diversas metodologias e tipos de ensaios mecânicos têm sido utilizados para o estudo das propriedades mecânicas de tecidos biológicos moles, tais como as artérias. O ambiente de carga a que uma artéria é submetida pode ser simulado in-vitro mediante testes de tração biaxial. Uma máquina de tração biaxial está sendo construída atualmente no Laboratório de Engenharia Ambiental e Biomédica da Escola Politécnica da Universidade de São Paulo. Para conduzir futuras pesquisas neste tipo de equipamento uma metodologia para a realização do teste e o processamento dos dados foi proposta e testada. Testes de tração biaxiais em aortas e subclávias suínas foram feitos para avaliar a metodologia. As amostras foram levadas até à ruptura nos ensaios. Curvas de tensão-deformação foram obtidas. O limite à ruptura e o limite elástico foram calculados. O modelo de Função de Energia de Deformação bidimensional para materiais hiperelásticos proposto por Fung e o modelo bicamada proposto por Holzapfel foram utilizados para realizar um ajuste dos dados experimentais. Um programa computacional foi implementado para o processamento dos dados e para estimar as constantes dos modelos matemáticos. Análises histológicas das amostras foram realizadas com o objetivo de estimar a média do conteúdo de colágeno e elastina no tecido. Resulta deste trabalho uma descrição de metodologia para caracterização de tecidos biológicos moles. / Several methods and types of mechanical tests have been used to study the mechanical properties of soft biological tissues such as arteries. The load environment that an artery is subjected can be simulated in vitro through biaxial tensile tests. A biaxial tensile machine is currently being built at the Laboratory of Biomedical and Environmental Engineering at the Polytechnic School of the University of São Paulo. To conduct further research on this kind of machine, a methodology for performing the test and data processing was proposed and tested. The biaxial tensile tests on aortas and subclavian porcine arteries were done to evaluate the methodology. The samples were tested up to the rupture. Stress-strain curves were obtained. The limit to rupture and the elastic limit were estimated. The two-dimensional model of strain energy function for hyperelastic materials proposed by Fung and the bilayer model proposed by Holzapfel were used to perform an adjustment of the experimental data. A computer program was implemented for data processing and to estimate the constants of the mathematical models. Histological analyses of the samples were performed in order to estimate the average content of collagen and elastin in the tissue. A description of the methodology for soft biological tissue characterization results from the present work.

Producing composite parts using low-cost processes such as resin transfer moulding (RTM) has received much interest in the aerospace industry. RTM manufactured components require near net shape preforms which closely fit mould cavities. To reduce labour costs associated with composite production, automated preforming processes must be utilized. However, obtaining reproducible high quality preforms is required for manufacturing consistent high quality parts. Stitched multilayer 3D non crimp fabric preforms are well suited for automation and an investigation into quality and performance of components manufactured from these preforms is required. This thesis provides an initial evaluation of quality and mechanical properties of components made from stitched multilayer 3D non crimp fabric preforms using RTM. Similar sized flat plates of varying fibre volume fractions were manufactured to evaluate flexural modulus and strength, short beam shear strength and drop weight impact resistance of the material. Also, integral reinforced panels (IRPs) featuring a reinforcing section joined to a flat plate of varying laminating sequences were manufactured to evaluate debonding strength between sections. Optical microscopy was performed on component samples to determine quality based on void content and was found to be within acceptable limits for production composites. Flexural moduli were found to be comparable with theoretical expected values, however flexural strength was limited by the presence of transverse stitches. Short beam shear strength results showed high consistency between specimens, however were lower than comparable values found in literature. Impact specimens showed consistency among specimens, with greater damage resistance than comparable values found in literature. Determining debonding strength proved difficult as different failure modes were observed between IRPs, however, initial baseline values were acquired.

Carbon fibre reinforced polymer matrix composites (CF PMCs) are increasingly used in state-of-the-art aerospace applications. Aerospace manufacturers favour components made of CF PMCs over those made of traditional metallic alloys because of their light weight and corrosion resistance, which lead to significant improvements in fuel consump- tion, increased payload capability, and reduced maintenance and inspection costs. How- ever, manufacturing of CF PMC components is performed differently than traditional material in all stages – design, prototyping and production – and therefore, many com- mercial manufacturers have only recently begun producing components with CF PMCs. The first half of this thesis was written as a contribution to the CRIAQ COMP-501 project, which focusses on investigating the cost-effective procurement of airframe com- ponents that are manufactured from final-thickness, net-shaped, and through-thickness reinforced CF preforms. Reinforcement preforms were assembled from commercial 2D woven fabric using stacks of various configurations of structural through-thickness CF stitch. The contribution herein provides the results obtained from investigations into the mechanical behaviour of the relevant reinforcements, when subjected to pre-infusion op- erations typical to RTM VARTM; mechanical behaviour in compaction, shear (draping) and bending (forming). The second half of this thesis presents the major developments which were made to an alternative process for producing thick 3D preforms with great versatility, a process originally proposed as a candidate for supplying preforms to the COMP-501 project. This process interfaces a proprietary kinematic drape optimization (CAD) software with proprietary automated dry fibre placement assembly (CAM) machinery to produce vari- able or final-thickness reinforcements which are highly-drapable and can lay steered tow yarns.

No description available.

No description available.

The asymmetrical arrangement of cellular structure allows for an accurate functional adaptation at all levels of hierarchy, which derives excellent features for the development of new materials. The main objective of introducing a hierarchy into cellular structures is to improve the mechanical behaviour of the material while maintaining its elastic properties. A part of this work is devoted to the literature review related to the lightened cellular polymeric materials with hierarchical cellular structure. The rest is focused on the preparation of PLA based polymer structures using 3D printing, followed by a saturation in CO2 and a foaming in a silicon oil at elevated temperature. Samples were prepared from natural and white PLA filaments. Based on a series of experiments, optimal conditions for the saturation and foaming process were identified. Through 3D printing and foaming, a one-, two- and three-level hierarchy was introduced into the beam-shaped samples and the effect of the internal cell arrangement on the strain response of the material was examined by the means of a mechanical three-point bending test. Increasing the level of the hierarchy led to an increase in material resistance, which resulted in high values of strength and strain energy (toughness) based on the samples density. The best results were achieved by samples with “sandwich” structure with three levels of hierarchy and 30% filling. Despite the shorter plateau, there was a significant increase in strength and strain energy compared to gradient structures. At the same time, the contribution of the polymer structures prepared in this field of research was demonstrated by comparison with the theoretical model.

Traditionally, the mechanical testing of ankle-foot orthoses (AFOs) has been performed with simple limb surrogates, typically with a single axis ankle joint and rigid foot and shank components. Since many current AFO designs allow 3D motion, a surrogate lower limb (SLL) that provides anatomically similar motion in all planes is needed to enable realistic load testing and cyclic testing in a controlled manner. The aim of this thesis was to design, fabricate and test a novel SLL that provides anatomically realistic 3D foot motion, based on a consensus of the passive lower limb range of motion (RoM) found in the literature. The SLL design was inspired by the Rizzoli model, sectioning the lower limb into five segments (shank, hindfoot, midfoot, forefoot, toes). Ball and socket joints were used for the shank-hindfoot, hindfoot-midfoot, and midfoot-forefoot. Forefoot-toes used a hinge-type joint. 3D printed flexible thermoplastic polyurethane (TPU) snap-fit connectors connected the 3D printed nylon foot blocks. A threaded ball stud connected the shank shaft and hindfoot. This shank shaft was surrounded by a 3D printed polylactic acid (PLA) shank cover. The foot was cast in silicone rubber to emulate soft tissue, with a PLA custom mould based on a Össur prosthetic foot cover model. The SLL was successfully designed for easy fabrication using readily available techniques, materials, and components. Only the metal shaft required additional machining. 3D printed components used an affordable 3D printer (Artillery Sidewinder X1), and readily available nylon, PLA, and TPU. Using motion capture testing, SLL foot rotation angles were found to be within standard deviation of mean foot passive rotation angle ranges found in the literature, showing that most joints were within 5° of target maximum rotation angles. With load testing, the SLL was shown to survive static loads representing 1.5 times body weight for a 100 kg individuals and cyclic loads representing normal gait loading for 500,000 cycles.