Acrylic bone cements modified with bioactive and biodegradable fillers

O cimento ósseo acrílico é o único material utilizado para a fixação de próteses em cirurgias ortopédicas, surgindo como uma alternativa às técnicas não cimentadas. Cerca de um milhão de pacientes são anualmente tratados para a substituição total da articulação do quadril e do joelho. Com a maior expectativa de vida da população e o aumento do número de cirurgias realizadas por ano espera-se que o uso do cimento ósseo aumente substancialmente. A fraca ligação do cimento ao osso é um problema comum que pode causar perda asséptica da prótese. Assim, torna-se necessário investir no desenvolvimento de cimentos ósseos alternativos que permitam promover maior estabilidade e melhor desempenho do implante. O principal objetivo desta tese foi desenvolver um cimento ósseo bioativo, capaz de ligar-se ao osso, com propriedades melhoradas relativamente aos sistemas convencionais. A preparação dos materiais foi realizada por dois processos diferentes, a polimerização por via térmica e a polimerização por via química. Inicialmente, utilizando o processo térmico, foram desenvolvidos compósitos de PMMA-co-EHA reforçados com vidro de sílica (CSi) e vidro de boro (CB) e comparados em termos do seu comportamento in vitro em meio acelular e celular. A formação de precipitados de fosfato de cálcio foi observada sobre a superfície de todos os compósitos indicando que estes materiais são potencialmente bioativos. Em relação à avaliação biológica o CSi demonstrou um efeito indutor da proliferação das células. As células apresentaram uma morfologia normal e alta taxa de crescimento quando comparadas com o padrão de cultura. Por outro lado ocorreu inibição da proliferação celular para o CB provavelmente devido à sua elevada taxa de degradação, levando a uma elevada concentraçao de iões de B e de Mg no meio de cultura. O efeito do vidro nos cimentos curados por via química, incorporando um activador de baixa toxicidade, também foi avaliado. Os resultados sugerem que as novas formulações podem diminuir o efeito exotérmico na cura do cimento e melhorar as propriedades mecânicas (flexão e compressão). Outro estudo conduzido neste trabalho explorou a possibilidade de incorporar ibuprofeno (fármaco anti-inflamatório) no cimento, dando origem a um material capaz de ser simultaneamente, bioativo e promotor da libertação controlada de fármacos. Neste contexto foi evidenciado que o desempenho do cimento desenvolvido pode contribuir para minimizar o processo inflamatório associado a uma cirurgia ortopédica. Finalmente, a fase sólida do cimento ósseo bioativo foi modificada por diferentes polímeros biodegradáveis. A adição deste enchimento deu origem a um cimento parcialmente biodegradável que pode permitir a formação de poros e o crescimento ósseo para o interior do cimento, resultando numa melhor fixação da prótese.

Accidental release of hazardous gases: modelling and assessing risk

The renewed concern in assessing risks and consequences from technological hazards in industrial and urban areas continues emphasizing the development of local-scale consequence analysis (CA) modelling tools able to predict shortterm pollution episodes and exposure effects on humans and the environment in case of accident with hazardous gases (hazmat). In this context, the main objective of this thesis is the development and validation of the EFfects of Released Hazardous gAses (EFRHA) model. This modelling tool is designed to simulate the outflow and atmospheric dispersion of heavy and passive hazmat gases in complex and build-up areas, and to estimate the exposure consequences of short-term pollution episodes in accordance to regulatory/safety threshold limits. Five main modules comprising up-to-date methods constitute the model: meteorological, terrain, source term, dispersion, and effects modules. Different initial physical states accident scenarios can be examined. Considered the main core of the developed tool, the dispersion module comprises a shallow layer modelling approach capable to account the main influence of obstacles during the hazmat gas dispersion phenomena. Model validation includes qualitative and quantitative analyses of main outputs by the comparison of modelled results against measurements and/or modelled databases. The preliminary analysis of meteorological and source term modules against modelled outputs from extensively validated models shows the consistent description of ambient conditions and the variation of the hazmat gas release. Dispersion is compared against measurements observations in obstructed and unobstructed areas for different release and dispersion scenarios. From the performance validation exercise, acceptable agreement was obtained, showing the reasonable numerical representation of measured features. In general, quality metrics are within or close to the acceptance limits recommended for ‘non-CFD models’, demonstrating its capability to reasonably predict hazmat gases accidental release and atmospheric dispersion in industrial and urban areas. EFRHA model was also applied to a particular case study, the Estarreja Chemical Complex (ECC), for a set of accidental release scenarios within a CA scope. The results show the magnitude of potential effects on the surrounding populated area and influence of the type of accident and the environment on the main outputs. Overall the present thesis shows that EFRHA model can be used as a straightforward tool to support CA studies in the scope of training and planning, but also, to support decision and emergency response in case of hazmat gases accidental release in industrial and built-up areas.

Micro/nanoreservoirs for controlled release of active species in smart functional coatings

This work reports one possible way to develop new functional coatings used to increase the life time of metallic structures. The functionalities selected and attributed to model coatings in the frame of this work were corrosion protection, self-sensing and prevention of fouling (antifouling). The way used to confer those functionalities to coatings was based on the encapsulation of active compounds (corrosion inhibitors, pH indicators and biocides) in micro and nanocontainers followed by their incorporation into the coating matrices. To confer active corrosion protection, one corrosion inhibitor (2-mercaptobenzothiazole, MBT) was encapsulated in two different containers, firstly in silica nanocapsules (SiNC) and in polyurea microcapsules (PU-MC). The incorporation of both containers in different models coatings shows a significant improvement in the corrosion protection of aluminum alloy 2024 (AA2024). Following the same approach, SiNC and PU-MC were also used for the encapsulation of phenolphthalein (one well known pH indicator) to introduce sensing properties in polymeric coatings. SiNC and PU-MC containing phenolphthalein acted as corrosion sensor, showing a pink coloration due to the beginning of cathodic reaction, resulting in a pH increase identified by those capsules. Their sensing performance was proved in suspension and when integrated in coatings for aluminium alloy 2024 and magnesium alloy AZ31. In a similar way, the biocide activity (antifouling) was assigned to two polymeric matrices using SiNC for encapsulation of one biocide (Dichloro-2-octyl-2H-isothiazol-3-one, DCOIT) and also SiNC-MBT was tested as biocide. The antifouling activity of those two encapsulated compounds was assessed through inhibition and consequent decrease in the bioluminescence of modified E. coli. That effect was verified in suspension and when incorporated in coatings for AISI 1008 carbon steel. The developed micro and nanocontainers presented the desired performance, allowing the introduction of new functionalities to model coatings, showing potential to be used as functional additives in the next generation of multifunctional coatings.