The meniscus is a soft, fibrocartilaginous tissue critical for the maintenance of normal knee biomechanics, providing shock absorbance and overall joint lubrication and stability. The adult tissue is highly avascular with a poor autonomous repair capacity in response to injury. Despite the estimated 850,000 arthroscopic surgeries performed per year to repair torn menisci and the increasing evidence showing a high incidence of meniscal degeneration during very early stages of osteoarthritis, little is currently known of the responses of meniscal fibrochondrocytes to physiological stimuli. Therefore, this work explored the responses of meniscal fibrochondrocytes to exogenous biomechanical and biochemical stimuli in an effort to better understand the sensitivity of these cells in their native tissue matrix as well as in a 3-D scaffold environment. Using the immature bovine model, the changes in biosynthesis of fibrochondrocytes in tissue explants and in an agarose scaffold due to unconfined oscillatory compression were explored. This biomechanical stimulus, previously identified to stimulate matrix production of chondrocytes of articular cartilage, stimulated total protein synthesis in both culture environments. In contrast, the synthesis of proteoglycans, matrix components important in mechanical stiffness and hydration of the tissue, was not affected by these compression protocols. However, the use of a biochemical stimulus in the form of anabolic cytokines significantly enhanced both protein and proteoglycan synthesis as a function of culture environment as well as type of cytokine used. The superposition of oscillatory compression in addition to the use of these potent biochemical stimulators, insulin-like growth factor-I or transforming growth factor-beta 1, did not further enhance matrix synthesis of fibrochondrocytes in agarose culture, suggesting an insensitivity of the fibrochondrocytes to biomechanical stimuli during early stages of matrix maturation within the agarose scaffold. As a combination of biomechanical and biochemical stimuli are responsible for directing the development, maintenance, and repair of the tissue, these findings aid in understanding fibrocartilage maintenance through studying responses in a tissue explant model. Additionally, studying agarose scaffolds aid in the understanding fibrocartilage development and deposition of a de novo matrix.

The alkali elements at ambient conditions are well described by the nearly-free electron (NFE) model, yet show a remarkable departure from this “simple” behaviour with increasing pressure. Low-symmetry complex structures are observed in all, and anomalous melting has been observed in lithium (Li), sodium (Na), rubidium (Rb), and caesium (Cs). In this Thesis, static and dynamic compression techniques have been used to investigate the high-pressure high-temperature behaviour of the alkali elements potassium (K) and Na. Utilising diamond anvil pressure cells and external resistive heating, both in-air and in-vacuum, the melting curve of K has been determined to 24 GPa and 750 K, and is found to be remarkably similar to that of Na, but strikingly different to that reported previously. Furthermore, there is some evidence to suggest that a change in the compressibility of liquid-K occurs at lower pressures than the solid-solid phase transitions, perhaps indicating structural transitions occurring in the liquid phase, similar to those in the underlying solid. This could suggest a mechanism to explain the anomalous melting behaviour observed. Previous ab initio computational studies indicate that the unusual melting curve of Na arises due to structural and electronic transitions occurring in the liquid, mirroring those found in the underlying solid at higher pressures. The discovery that the melting curve of K is very similar to that of Na suggests that the same physical phenomena predicted for Na could be responsible for the high-pressure melting behaviour observed in K. The tI19 phase of K, observed above 20 GPa at 300 K, is a composite incommensurate host-guest structure consisting of 1D chains of guest atoms surrounded by a tetragonal host framework. Along the unique c-axis, the host and guest are incommensurate with each other. During the melting studies described above, it was observed that with increasing temperature, the weaker-bonded guest chains become more disordered while the host structure remains unchanged. To investigate and characterise this order-disorder transition, in situ synchrotron X-ray diffraction studies were conducted on single-crystal and quasi-single crystal samples of tI19-K. An order-disorder phase line has been mapped out to 50 GPa and 650 K. Perhaps the most striking departure from NFE behaviour in the alkali elements is observed in Na at pressures above 200 GPa where it transforms to a transparent electrical insulator. This phase is a so-called elemental “electride”, which may be thought of as being pseudo-ionically bonded. Electrides are predicted to exist in many elements, but at pressures far beyond the current capabilities of static pressure techniques. Utilising laser-driven quasi-isentropic compression techniques, dynamic compression experiments were performed on Na to see if it is possible to observe this electride phase under the timescales of dynamic compression experiment (ns). Optical velocimetry and reflectivity of the sample were measured directly to determine pressure and monitor the on-set of the transparent phase, respectively.

Nos sistemas de revestimento de fundo de aterros sanitários e pilhas de rejeito de mineração, é comum utilizar geotêxtil não-tecido para a proteção ao puncionamento da geomembrana por objetos pontiagudos como a brita. Neste trabalho, realiza-se um estudo experimental a fim de avaliar a superfície deformada de geomembrana de PEAD, com 2 mm de espessura, em camada de proteção sujeita a carregamentos de 600 kPa e 1800 kPa ao longo de 100 h, com o objetivo de simular danos mecânico de operação. Para a leitura da superfície deformada da geomembrana utilizou-se um lençol de chumbo localizado sob a geomembrana e as suas deformações foram estimadas a partir de uma máquina de leitura por coordenadas, com grid de 4 mm. Além deste, foi estimada a superfície deformada da geomembrana para o grid de 1 mm, com a aplicação do método de interpolação chamado de triangulação. Ainda foram utilizados extensômetros elétricos para estimar deformações pontuais na geomembrana. A fim de prevenir o puncionamento da geomembrana e limitar a sua deformação, utilizou-se como camada de proteção quatro geotêxteis não tecidos do tipo PP com massa por unidade de área variando entre 550 e 1300 g/m2, e uma camada de 10 cm de argila. Para a carga de 600 kPa, todas as camadas de proteção foram eficientes para evitar o puncionamento da geomembrana e limitar a sua deformação em 6%. Na carga de 1800 kPa, para proteção de geotêxtil, as configurações duplas tiveram melhor desempenho com valores de deformações menores que 6%, e a camada de 10 cm de argila foi ainda mais eficaz. Por fim, o trabalho mostrou que a superfície deformada decorrente do tipo de proteção adotado também é influenciada pelo grau de compactação do solo, o tipo de brita, a carga aplicada e as propriedades físicas do elemento de proteção. / In landfill backfill systems and mining tailings piles, it is common to use nonwoven geotextiles to protect geomembrane punctures by sharp objects such as gravel. In this work, an experimental study was carried out to evaluate the deformed HDPE geomembrane surface, with a thickness of 2 mm, under a protective layer subjected to loads of 600 kPa and 1800 kPa over 100 h, with the objective of Simulate mechanical damage of operation. To read the deformed surface of the geomembrane was used a sheet of lead located under the geomembrane and its deformations were estimated from a machine of reading by coordinates, with grid of 4 mm. Also, the deformed surface of the geomembrane was estimated for the grid of 1 mm, with the application of the interpolation method called triangulation. Electrical extensometers were also used to estimate point deformations in the geomembrane. In order to prevent the puncture of the geomembrane and to limit its deformation, four non-woven PP-type geotextiles with a mass per unit area ranging from 550 to 1300 g/m2 and a layer of 10 cm of clay. At the load of 600 kPa, all the layers of protection were efficient to avoid the puncture of the geomembrane and to limit its deformation in 6%. In the vertical load of 1800 kPa, for geotextile protection, the double configurations had better performance with deformation values lower than 6%, and the 10 cm layer of clay was even more effective. Finally, the work showed that the deformed surface resulting from the type of protection adopted is also influenced by the degree of soil compaction, the type of gravel, the applied load and the physical properties of the protection element.

Nos sistemas de revestimento de fundo de aterros sanitários e pilhas de rejeito de mineração, é comum utilizar geotêxtil não-tecido para a proteção ao puncionamento da geomembrana por objetos pontiagudos como a brita. Neste trabalho, realiza-se um estudo experimental a fim de avaliar a superfície deformada de geomembrana de PEAD, com 2 mm de espessura, em camada de proteção sujeita a carregamentos de 600 kPa e 1800 kPa ao longo de 100 h, com o objetivo de simular danos mecânico de operação. Para a leitura da superfície deformada da geomembrana utilizou-se um lençol de chumbo localizado sob a geomembrana e as suas deformações foram estimadas a partir de uma máquina de leitura por coordenadas, com grid de 4 mm. Além deste, foi estimada a superfície deformada da geomembrana para o grid de 1 mm, com a aplicação do método de interpolação chamado de triangulação. Ainda foram utilizados extensômetros elétricos para estimar deformações pontuais na geomembrana. A fim de prevenir o puncionamento da geomembrana e limitar a sua deformação, utilizou-se como camada de proteção quatro geotêxteis não tecidos do tipo PP com massa por unidade de área variando entre 550 e 1300 g/m2, e uma camada de 10 cm de argila. Para a carga de 600 kPa, todas as camadas de proteção foram eficientes para evitar o puncionamento da geomembrana e limitar a sua deformação em 6%. Na carga de 1800 kPa, para proteção de geotêxtil, as configurações duplas tiveram melhor desempenho com valores de deformações menores que 6%, e a camada de 10 cm de argila foi ainda mais eficaz. Por fim, o trabalho mostrou que a superfície deformada decorrente do tipo de proteção adotado também é influenciada pelo grau de compactação do solo, o tipo de brita, a carga aplicada e as propriedades físicas do elemento de proteção. / In landfill backfill systems and mining tailings piles, it is common to use nonwoven geotextiles to protect geomembrane punctures by sharp objects such as gravel. In this work, an experimental study was carried out to evaluate the deformed HDPE geomembrane surface, with a thickness of 2 mm, under a protective layer subjected to loads of 600 kPa and 1800 kPa over 100 h, with the objective of Simulate mechanical damage of operation. To read the deformed surface of the geomembrane was used a sheet of lead located under the geomembrane and its deformations were estimated from a machine of reading by coordinates, with grid of 4 mm. Also, the deformed surface of the geomembrane was estimated for the grid of 1 mm, with the application of the interpolation method called triangulation. Electrical extensometers were also used to estimate point deformations in the geomembrane. In order to prevent the puncture of the geomembrane and to limit its deformation, four non-woven PP-type geotextiles with a mass per unit area ranging from 550 to 1300 g/m2 and a layer of 10 cm of clay. At the load of 600 kPa, all the layers of protection were efficient to avoid the puncture of the geomembrane and to limit its deformation in 6%. In the vertical load of 1800 kPa, for geotextile protection, the double configurations had better performance with deformation values lower than 6%, and the 10 cm layer of clay was even more effective. Finally, the work showed that the deformed surface resulting from the type of protection adopted is also influenced by the degree of soil compaction, the type of gravel, the applied load and the physical properties of the protection element.