Nos dias atuais, grande parte das intervenções cirúrgicas inclui o implante de materiais. Os grandes obstáculos na implantação de próteses em organismos humanos são a coagulação sanguínea em contato com o material devido ao alto grau de ativação plaquetária e a compatibilidade dos tecidos biológicos ao material implantado. Agregando melhorias de propriedades mecânicas a superfícies biocompatíveis, materiais poliméricos apresentam grandes tendências a serem excelentes candidatos a biomateriais para tais aplicações. O objetivo deste trabalho foi realizar modificações superficiais em polímeros através do método de implantação por feixe iônico a fim de se investigar mudanças induzidas em suas propriedades superficiais e estudar possíveis mudanças em sua biocompatibilidade, em específico, sua hemocompatibilidade. Amostras de policarbonato foram irradiadas com feixes de íons de argônio com energia 23 keV e cinco diferentes doses. As superfícies das amostras foram analisadas com medidas de ângulo de contato, microscopia de força atômica, espectroscopia de massa de íons secundários, espectroscopia de fotoelétrons, espectroscopia de retroespalhamento Rutherford, deteção de recuo elástico, espectroscopia de raios-X induzidos por partículas e testes de adesão plaquetária. Os resultados das diferentes técnicas apontaram de forma consistente a uma série de alterações químicas e físicas induzidas nas superfícies das amostras, dentre elas: a perda significativa de hidrogênio nas amostras irradiadas, aumento do grau de reticulação entre as cadeias poliméricas que levou ao aumento de elétron deslocalizados e mudança de coloração, remoção de aditivos, migração à superfície de átomos de argônio implantados e alteração de hidrofilicidade. Ao confrontar todos os resultados obtidos com os resultados dos testes de adesão plaquetária, constatou-se que os efeitos observados aumentam o caráter trombogênico da superfície do policarbonato e que a remoção de aditivos com grupos sulfato e sulfonato após irradiação com argônio teve grande influência em tal aumento. / In the current days, a big part of the surgical interventions includes the implant of materials. The great obstacles for prosthesis implantation in living organisms are the blood clotting when in contact to the material due to a high level of platelet activation and the biological tissues compatibility to the implanted material. By joining improvements on mechanical properties to biocompatible surfaces, polymer materials present high tendencies to be excellent biomaterials candidates for such applications. The objective of this work was to perform surface modification in polymers through the ion beam implantation method in order to investigate changes induced in their surface properties and study possible biocompatibility changes. Samples of polycarbonate were irradiated with argon ion beam with 23 keV energy and different doses. The surfaces of the samples were analyzed by contact angle measurements, atomic force microscopy, secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, elastic recoil detection, particle induced x-ray spectroscopy and platelet adhesion tests. The results from the different techniques pointed consistently to a series of chemical and physical changes induced on the samples\' surfaces, such as: significant loss of hydrogen for the irradiated samples, increase of cross-linking between polymer chains which led to the increase of delocalized electrons and color change, removal of additives, migration of argon atoms to the surface and hydrophilicity changes. By comparing all the obtained results to the platelet adhesion tests results, it was found that the observed effects increase the thrombogenic characteristic of the polycarbonate surface and that the removal of additives with sulfate and sulfonate groups after the argon irradiation had great influence on such increase.

No description available.

[ES] Esta Tesis ha sido dedicada al modelado multiescala considerando al anfitrión celular para el análisis y ajuste de circuitos genéticos sintéticos para bioproducción. Los objetivos principales fueron: 1. El desarrollo de un modelo que considere el anfitrión celular de tamaño reducido enfocado para simulación y análisis. 2. El desarrollo de herramientas de programación para el modelado y la simulación, orientada a la biología sintética. 3. La implementación de un modelo multiescala que considere las escalas relevantes para la bioproducción (biorreactor, célula y circuito sintético). 4. El análisis del controlador antitético considerando las interacciones célula-circuito, como ejemplo de aplicación de las herramientas desarrolladas. 5. El desarrollo y la validación experimental de leyes de control robusto para biorreactores continuos. El trabajo presentado en esta Tesis cubre las tres escalas del proceso de bioproducción. La primera escala es el biorreactor: esta escala considera la dinámica macroscópica del sustrato y la biomasa, y como estas dinámica se conecta con el estado interno de las células. La segunda escala es la célula anfitriona: esta escala considera la dinámica interna de la célula y la competencia por los recursos limitados compartidos para la expresión de proteínas. La tercera escala es el circuito genético sintético: esta escala considera la dinámica de expresión de los circuitos sintéticos exógenos y la carga que inducen en la célula anfitriona. Por último, como <<cuarta>> escala, parte de la Tesis se ha dedicado a desarrollar herramientas de software para el modelado y la simulación. Este documento se divide en siete capítulos. El Capítulo 1 es una introducción general al trabajo de la Tesis y su justificación; también presenta un mapa visual de la Tesis y enumera las principales contribuciones. El Capítulo 2 muestra el desarrollo del modelo del anfitrión celular (los Capítulos 4 y 5 hacen uso de este modelo para sus simulaciones). El Capítulo 3 presenta OneModel: una herramienta de software desarrollada en la Tesis que facilita el modelado y la simulación en biología sintética, en particular, facilita el uso del modelo del anfitrión celular. El Capítulo 4 utiliza el modelo del anfitrión celular para montar el modelo multiescala que considera el biorreactor y analiza el título, la productividad y el rendimiento en la expresión de una proteína exógena. El Capítulo 5 analiza un circuito más complejo, el recientemente propuesto y muy citado controlador biomolecular antitético, utilizando el modelo del anfitrión celular. El Capítulo 6 muestra el diseño de estrategias de control no lineal que permiten controlar la concentración de biomasa en un biorreactor continuo de forma robusta. El Capítulo 7 resume y presenta las principales conclusiones de la Tesis. En el Apéndice A se muestra el desarrollo teórico del modelo del anfitrión celular. Esta Tesis destaca la importancia de estudiar la carga celular en los sistemas biológicos, ya que estos efectos son muy notables y generan interacciones entre circuitos aparentemente independientes. La Tesis proporciona herramientas para modelar, simular y diseñar circuitos genéticos sintéticos teniendo en cuenta estos efectos de carga y permite el desarrollo de modelos que conecten estos fenómenos en los circuitos genéticos sintéticos, que van desde la dinámica intracelular de la expresión génica hasta la dinámica macroscópica de la población de células dentro del biorreactor. / [CA] Aquesta Tesi tracta del modelat multiescala considerant l'amfitrió ce\lgem ular per a l'anàlisi i ajust de circuits genètics sintètics per a bioproducció. Els objectius principals van ser: 1. El desenvolupament d'un model de grandària reduïda que considere l'amfitrió ce\lgem ular, enfocat al seu ús en simulació i anàlisi. 2. El desenvolupament d'eines de programari per al modelatge i la simulació, orientada a la biologia sintètica. 3. La implementació d'un model multiescala que considere les escales rellevants per a la bioproducció (bioreactor, cè\lgem ula i circuit sintètic). 4. L'anàlisi del controlador antitètic considerant les interacciones cè\lgem ula-circuit, com a exemple d'aplicació de les eines desenvolupades. 5. El desenvolupament i la validació experimental de lleis de control robust per a bioreactors continus. El treball presentat en aquesta Tesi cobreix les tres escales del procés de bioproducció. La primera escala és el bioreactor: aquesta escala considera la dinàmica macroscòpica del substrat i la biomassa, i com aquestes dinàmiques es connecten amb l'estat intern de les cè\lgem ules. La segona escala és la cè\lgem ula amfitriona: aquesta escala considera la dinàmica interna de la cè\lgem ula i la competència pels recursos limitats compartits per a l'expressió de proteïnes. La tercera escala és la del circuit genètic sintètic: aquesta escala considera la dinàmica d'expressió de circuits sintètics exógens i la càrrega que indueixen en la cè\lgem ula amfitriona. Finalment, com a <<quarta>> escala, part de la Tesi s'ha dedicat a desenvolupar eines de programari per al modelatge i la simulació. Aquest document es divideix en set capítols. El Capítol 1 és una introducció general al treball de la Tesi i la seua justificació; també presenta un mapa visual de la Tesi i enumera les principals contribucions. El Capítol 2 mostra el desenvolupament del model de l'amfitrió ce\lgem ular (els Capítols 4 i 5 fan ús d'aquest model per a les seues simulacions). El Capítol 3 presenta OneModel: una eina de programari desenvolupada en la Tesi que facilita el modelatge i la simulació en biologia sintètica, en particular, facilita l'ús del model de l'amfitrió ce\lgem ular. El Capítol 4 utilitza el model de l'amfitrió ce\lgem ular per a muntar el model multiescala que considera el bioreactor i analitza el títol, la productivitat i el rendiment en l'expressió d'una proteïna exògena. El Capítol 5 analitza un circuit més complex, el recentment proposat i molt citat controlador biomolecular antitètic, utilitzant el model de l'amfitrió ce\lgem ular. El Capítol 6 mostra el disseny d'estratègies de control no lineal que permeten controlar la concentració de biomassa en un bioreactor continu de manera robusta. El Capítol 7 resumeix i presenta les principals conclusions de la Tesi. En l'Apèndix A es mostra el desenvolupament teòric del model de l'amfitrió ce\lgem ular. Aquesta Tesi destaca la importància d'estudiar la càrrega ce\lgem ular en els sistemes biològics, ja que aquests efectes són molt notables i generen interaccions entre circuits aparentment independents. La Tesi proporciona eines per a modelar, simular i dissenyar circuits genètics sintètics tenint en compte aquests efectes de càrrega i permet el desenvolupament de models que connecten aquests fenòmens en els circuits genètics sintètics, que van des de la dinàmica intrace\lgem ular de l'expressió gènica fins a la dinàmica macroscòpica de la població de cè\lgem ules dins del bioreactor. / [EN] This Thesis was devoted to the multi-scale host-aware analysis and tuning of synthetic gene circuits for bioproduction. The main objectives were: 1. The development of a reduced-size host-aware model for simulation and analysis purposes. 2. The development of a software toolbox for modeling and simulation, oriented to synthetic biology. 3. The implementation of a multi-scale model that considers the scales relevant to bioproduction (bioreactor, cell, and synthetic circuit). 4. The host-aware analysis of the antithetic controller, as an example of the application of the developed tools. 5. The development and experimental validation of robust control laws for continuous bioreactors. The work presented in this Thesis covers the three scales of the bioproduction process. The first scale is the bioreactor: this scale considers the macroscopic substrate and biomass dynamics and how these dynamics connect to the internal state of the cells. The second scale is the host cell: this scale considers the internal dynamics of the cell and the competition for limited shared resources for protein expression. The third scale is the synthetic genetic circuit: this scale considers the dynamics of expressing exogenous synthetic circuits and the burden they induce on the host cell. Finally, as a <<fourth>> scale, part of the Thesis was devoted to developing software tools for modeling and simulation. This document is divided into seven chapters. Chapter 1 is an overall introduction to the Thesis work and its justification; it also presents a visual map of the Thesis and lists the main contributions. Chapter 2 shows the development of the host-aware model (Chapters 4 and 5 make use of this model for their simulations). Chapter 3 presents OneModel: a software tool developed in the Thesis that facilitates modeling and simulation for synthetic biology---in particular, it facilitates the use of the host-aware model---. Chapter 4 uses the host-aware model to assemble the multi-scale model considering the bioreactor and analyzes the titer, productivity (rate), and yield in expressing an exogenous protein. Chapter 5 analyzes a more complex circuit, the recently proposed and highly cited antithetic biomolecular controller, using the host-aware model. Chapter 6 shows the design of nonlinear control strategies that allow controlling the concentration of biomass in a continuous bioreactor in a robust way. Chapter 7 summarizes and presents the main conclusions of the Thesis. Appendix A shows the theoretical development of the host-aware model. This Thesis emphasizes the importance of studying cell burden in biological systems since these effects are very noticeable and generate interactions between seemingly unconnected circuits. The Thesis provides tools to model, simulate and design synthetic genetic circuits taking into account these burden effects and allowing the development of models that connect phenomena in synthetic genetic circuits, ranging from the intracelullar dynamics of gene expression to the macroscopic dynamics of the population of cells inside the bioreactor. / This research was funded by MCIN/AEI/10.13039/501100011033 grant number PID2020-117271RB-C21, and MINECO/AEI, EU grant number DPI2017-82896- C2-1-R. The author was recipient of the grant “Programa para la Formación de Personal Investigador (FPI) de la Universitat Politècnica de València — Subprograma 1 (PAID-01-2017)”. The author was also a grantee of the predoctoral stay “Ayudas para Movilidad de Estudiantes de Doctorado de la Universitat Politècnica de València 2019”. The Control Theory and Systems Biology Lab of the ETH Zürich is acknowledged for accepting the author in their facilities as predoctoral stay and their valuable collaboration sharing knowledge. / Santos Navarro, FN. (2022). Multi-Scale Host-Aware Modeling for Analysis and Tuning of Synthetic Gene Circuits for Bioproduction [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/183473 / TESIS / Premios Extraordinarios de tesis doctorales

Pour assurer l'entretien des voies navigables, les sédiments de canaux sont régulièrement curés et généralement mis en dépôt. Cette pratique peut s'avérer dangereuse pour l'environnement lorsque ces sédiments sont contaminés. Le but de ce travail était d'identifier la spéciation du zinc dans un sédiment pollué et dans le sol sous-jacent après dépôt. Le transfert du zinc du sédiment vers le sol au cours du temps a été suivi par analyse des eaux, du sédiment et du sol. Les formes chimiques du zinc dans les phases solides ont été déterminées en combinant des techniques de micro-analyse (MEB-EDS, u-PIXE, u-RBS, u-SXRF) et la spectroscopie EXAFS, après fractionnement physique et chimique des échantillons. Les spectres EXAFS ont été exploités par analyse en composantes principales. Les principaux résultats de ce travail sont les suivants: * Dans le sédiment initial, le zinc est majoritairement présent sous forme de sphalérite (ZnS) et associé aux oxyhydroxydes de fer mal cristallisés. Trois espèces minoritaires, la willémite (Zn2SiO4), la zincite (ZnO) et un phyllosilicate zincifère ont été également identifiées. La présence de willémite, de zincite, et d'au moins une partie de la sphalérite, est attribuée aux activités anthropiques de grillage du minerai de zinc. La fixation d'une partie du zinc par les oxyhydroxydes de fer et les phyllosilicates résulte de l'altération des minéraux primaires. * L'oxydation des sulfures est le processus majeur contribuant à la mise en solution du zinc au cours du temps. La réduction des oxyhydroxydes de fer survenant lors des périodes d'hydromorphie concourt, dans une moindre mesure, à la mise en solution du zinc associé. * Au cours du temps, la proportion de ZnS diminue dans le sédiment au profit des formes secondaires. Un enrichissement en zinc a été mesuré après 16 mois de dépôt dans les premiers centimètres du sol sous-jacent. La majorité du zinc est alors sous forme de ZnS du fait d'une importante migration particulaire per descensum. Une autre partie du métal présent dans le sol est associée aux phyllosilicates et oxyhydroxydes de fer. Les conditions physico-chimiques du milieu (pH, Eh, concentrations en zinc, silice et fer dissous) sont favorables à la précipitation du zinc et de la silice libre sous forme de phyllosilicate zincifère, et à celle du fer dissous sous forme d'oxyhydroxydes de fer amorphes susceptibles de fixer le zinc. * Les bilans géochimiques montrent que la quantité de zinc exportée en solution, pendant la période de suivi du dépôt (16 mois), est faible en regard du stock contenu dans le sédiment, mais que cette quantité augmente de façon significative au cours du temps. Cependant, la majorité du zinc exporté en solution est vraisemblablement refixée par les phases d'altération. * Les phases d'altération comme les oxyhydroxydes de fer et les phyllosilicates pourraient être exploitées à des fins de rémédiation.

Este trabalho trata do problema de alocação de estações rádio base (ERBs) para o sistema de telefonia celular de 4G, que no Brasil utiliza o protocolo LTE (Long Term Evolution). Tal problema consiste em dada uma determinada região geográfica, onde se encontram os possíveis clientes, dispor antenas de modo a cobrir a maior área possível da região em estudo, levando em consideração a capacidade de cada antena em atender os clientes com qualidade de serviço. O algoritmo apresentado calcula o raio de alcance da ERB, a quantidade mínima de ERBs necessárias para cobrir a região em estudo e a localização de cada ERB. Para que o algoritmo pudesse ser desenvolvido foi investigado o sistema de comunicação LTE, modelos de propagação de sinal além do algoritmo memético, visto que a alocação de ERBs é um problema NP-difícil. Para o raio de ação da célula foi considerado, além do modelo de propagação, o calculo de link budget, throughput e relação sinal ruído. Por fim, uma comparação entre o LTE operando nas faixas de frequências de 700 MHz e 2,5 GHz foi realizado. O algoritmo de alocação de ERBs se mostrou eficiente cobrindo mais de 80% da área de estudo em 29 dos 30 casos analisados. Com relação a frequência, o LTE se mostrou mais adequado operando em 700 MHz pois a quantidade de ERBs para cobertura da área de estudo é menor se comparado a frequências de 2,5 GHz. / This work deals with the issue of radio base stations (RBSs) allocation for the 4G cell phone system, which in Brazil uses the LTE (Long Term Evolution) protocol. Such problem consists in a certain geographical region, where potential customers might be found, having antennas to cover the largest possible area of the region under study, taking into account the capacity of each antenna to serve customers with quality of service. The presented algorithm calculates the range of the RBS station, the minimum amount of necessary RBS to cover the area under study and the location of each RBS. In order to the algorithm to be developed the LTE communication system was investigated, signal propagation models beyond memetic algorithm, since the RBS allocation is a NP-hard problem. For the cell’s range of action it was considered, besides the model of propagation, the link budget calculation, throughput and noise signal relation. Therefore, a comparison between LTE operating on 700 MHz and 2,5 GHz frequencies was made. The RBS allocation algorithm was efficient covering more than 80% of the study area in 29 from the 30 analyzed cases. In relation to the frequency, LTE was considered more adequate operating on 700 MHz, for the quantity of RBS to cover the study area is smaller, if compared to 2,5 GHz frequencies.

Made available in DSpace on 2015-04-14T14:41:44Z (GMT). No. of bitstreams: 1 446798.pdf: 17400130 bytes, checksum: 8c4ff206b301a01d7270a28ca01a13df (MD5) Previous issue date: 2013-03-26 / The present study investigates how the middle classes - the social strata that have shown the most growth in numbers in Brazil in the past few years - think of Jornal do Almo?o, the most traditional TV news program in southern Brazil, produced by RBS TV. We researched the history and the production of the show that has been aired at noon for more than 40 years now. Social and economical questionnaires were conducted with the viewers as well as comprehensive surveys to assess what they want to watch in midday TV, specially in Jornal do Almo?o. By analyzing habits, costumes, preferences and opinions of these viewers, we investigated the &#8213;ritual&#8214; of watching Jornal do Almo?o. Details like where the TV set was placed in the house, parallel activities taken while the show was on and the viewers reactions to what was presented were also taken into account. These observations were confronted with the changes in the program, implemented from 2010, as part of &#8213;RBS?s plan of action&#8214; which made Jornal do Almo?o into a more news and entertainment oriented attraction. To emphasize the daily ritual of watching the program, we adopted the Media and Cultural Theory as a model, specially de Institutionality, technicity and rituality by Jes?s Marin-Barbero (2009). In general, our study shows that the middle classes are interested in news and want to keep themselves up to date, even though they consider that the program is primarily aimed at more popular classes than their own, i.e. classes D and E. Thus, it would be possible to ascertain that the content of Jornal do Almo?o, even after the changes it went through, is still somehow disconnected with the middle class proper - which is the foundation of its audience / Esta pesquisa possui como objetivo geral investigar como integrantes da classe m?dia, categoria econ?mica e social que mais cresceu nos ?ltimos anos no Brasil, veem o Jornal do Almo?o da RBS TV e o que querem assistir neste programa. A partir de uma observa??o da hist?ria e da produ??o do JA, de aplica??o de question?rio socioecon?mico a telespectadores do programa, de acompanhamento do programa por uma semana junto aos informantes e de imers?o no cotidiano dos mesmos, mediante pesquisa em profundidade, foi poss?vel compreender como integrantes da classe m?dia (C) veem e tamb?m o que querem ver ao meio-dia na TV, especificamente no Jornal do Almo?o da RBS TV. Investigamos, assim, o &#8213;ritual&#8214; que comp?e o assistir ao Jornal do Almo?o, analisando os h?bitos e costumes de nossos entrevistados, as suas prefer?ncias e opini?es, e observando o local da televis?o na casa, quais as companhias no momento da recep??o, a aten??o dispensada ao programa, as atividades paralelas e as respectivas rea??es dos telespectadores. Tudo isso frente ?s mudan?as operadas no telejornal em 2010, com base num &#8213;plano de a??o&#8214; da RBS, que transformou o programa em um espa?o de not?cias e entretenimento. A ?nfase diz respeito aos rituais cotidianos de assist?ncia do telejornal; por essa raz?o, toma-se os Estudos Culturais como perspectiva de abordagem, adotando-se como modelo te?rico-metodol?gico a teoria das media??es culturais: em especial, institucionalidade, tecnicidade e ritualidade, de Jes?s Mart?n-Barbero (2009). De modo geral, a pesquisa conclui que a classe m?dia gosta de not?cias e quer estar sempre bem informada sobre tudo o que acontece, entretanto, considera que o programa do meio-dia da RBS ? muito voltado para as classes mais populares (D e E). Sendo assim, ? poss?vel afirmar que o conte?do produzido, depois das mudan?as feitas no Jornal do Almo?o, ainda n?o conseguiu conquistar e ajustar-se a esse estrato econ?mico classe m?dia que forma a base de sua audi?ncia.

Due to the extreme properties of diamond, such as extreme hardness, high thermal conductivity, high electrical breakdown strength, high electron and hole mobilities and large band gap, it is of interest to study this material in detail. Before advantage can be taken of diamond’s properties for high-temperature, high-power electronic applications successful doping/ion implantation of diamond must be achieved. This requires an understanding of the types of defects produced during ion irradiation. In the present work, type IIa diamond has been irradiated with various doses of 320keV Xe ions at room temperature. Analytical techniques used are electron spin resonance spectroscopy, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. Previous models have suggested that upon ion impact, amorphous and/or graphitized clusters are formed in diamond, which will overlap at a critical dose to form a semi-continuous graphitized layer. (For complete abstract open document)

Due to the extreme properties of diamond, such as extreme hardness, high thermal conductivity, high electrical breakdown strength, high electron and hole mobilities and large band gap, it is of interest to study this material in detail. Before advantage can be taken of diamond’s properties for high-temperature, high-power electronic applications successful doping/ion implantation of diamond must be achieved. This requires an understanding of the types of defects produced during ion irradiation. In the present work, type IIa diamond has been irradiated with various doses of 320keV Xe ions at room temperature. Analytical techniques used are electron spin resonance spectroscopy, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. Previous models have suggested that upon ion impact, amorphous and/or graphitized clusters are formed in diamond, which will overlap at a critical dose to form a semi-continuous graphitized layer. (For complete abstract open document)

La connaissance des vitesses de diffusion du plomb dans la monazite est indispensable pour comprendre les anomalies des âges U-Th-Pb de ce minéral, qui est un des plus utilisés en géochronologie après le zircon. <br />Des expériences de diffusion ont été faites dans des monocristaux de NdPO4 et des polycristaux de Nd0.66Ca0.17Th0.17PO4 à partir de couches minces de Nd0.66Pb0.17Th0.17PO4, pour étudier les échanges Pb2+ + Th4+ 2 Nd3+ et Pb2+ Ca2+. Les recuits de diffusion ont été effectués entre 1200 et 1500°C, à pression ambiante, pour des durées comprises entre une heure et un mois. Les profils de diffusion ont été analysés en MET et en RBS. <br />Les diffusivités extraites pour l'échange Pb2+ + Th4+ 2 Nd3+ suivent une loi d'Arrhenius de paramètres E = 509 ± 24 kJ mol-1 et log D0 (m2 s-1) = -3.41 ± 0.77. Les données préliminaires pour l'échange Pb2+ Ca2+ concordent avec ce résultat. <br />L'extrapolation de nos données aux températures crustales donne de très faibles diffusivités. Par exemple, le temps nécessaire pour qu'un grain de monazite de 50 µm perde tout son plomb à 800°C est supérieur à l'âge de la Terre. <br />De ces résultats et d'autres évidences de la littérature, nous concluons que la plupart des perturbations des âges U-Th-Pb des monazites ne peut pas être attribuée à la diffusion du plomb à l'état solide, mais plus vraisemblablement à des interactions avec des fluides

Lorsque les verres bioactifs entrent en contact avec des tissus vivants, une série de réactions physico-chimiques (dissolution, précipitation...) ont lieu à l'interface matériau / os, et conduisent à la formation d'une couche phosphocalcique, dont la composition est proche de la phase minérale de l'os (hydroxyapatite). La couche d'apatite sert de site de minéralisation pour les cellules osseuses, ce qui permet in fine un lien intime entre le verre bioactif et les tissus osseux. Ce lien est caractéristique de la bioactivité, qui peut être modulée via plusieurs paramètres du verre comme la composition en éléments majeurs et traces ou les propriétés texturales (surface spécifique, porosité).Dans ce contexte, nous avons élaboré des verres bioactifs dans des systèmes binaires (SiO2-CaO) et ternaires (SiO2-CaO-P2O5). Ces verres ont été dopés en ions zinc et magnésium via la voie sol-gel. Grâce à l'emploi de tensioactifs, nous avons obtenu des verres mésostructurés. Enfin, en utilisant des méthodes dites " d'opale inverse ", des verres à macroporosité organisée ont été synthétisés. L'influence de ces paramètres sur la réactivité des verres au contact d'un milieu biologique (DMEM) a principalement été étudiée par des techniques utilisant des microfaisceaux d'ions. L'émission X induite par particules chargées (PIXE) combinée à la spectrométrie de rétrodiffusion Rutherford (RBS) a en effet démontré des effets évidents sur la cinétique, l'amplitude et la distribution spatiale des réactions physico-chimiques.