Surface modification of zirconia-based bioceramics for orthopedic and dental applications

Debido a sus excelentes propiedades mecánicas y una excelente biocompatibilidad, el uso de las cerámicas de base de circona en aplicaciones dentales y ortopédicas ha crecido rápidamente durante las últimas décadas. Sin embargo, tanto la alúmina como la circona son bioinertes, lo cual dificulta su implantación en contacto directo con el hueso. Además, las infecciones siguen siendo una de las principales causas de fallo de implantes. Para resolver ambos problemas, se requiere un mejor diseño de la superficie: en particular, una topografía adecuada puede promover la osteointegración y limitar la adhesión bacteriana. Por otro lado, la fiabilidad a largo plazo es un asunto crítico para los implantes estructurales, y las cerámicas que contienen circona requieren una atención especial. Como para otras cerámicas, las alteraciones superficiales pueden comprometer sus propiedades mecánicas. Además, la transformación de fase de tetragonal a monoclínica, que les proporciona una tenacidad excepcional, puede ocurrir espontáneamente en presencia de agua, lo cual puede afectar las propiedades del material. La cinética de este fenómeno, conocido como envejecimiento hidrotérmico, es muy sensible a los cambios de procesamiento. Por lo tanto, cualquier modificación de la superficie debe ir acompañada de una evaluación de su impacto en la fiabilidad de los implantes. Basado en estas observaciones, el objetivo de esta tesis fue desarrollar procesos para modificar la superficie de los implantes a base de circona, en particular la topografía, sin comprometer sus propiedades mecánicas y estabilidad hidrotérmica. El esfuerzo de investigación se centró en dos materiales: la circona estabilizada con itria (3Y-TZP), que se utiliza cada vez más para aplicaciones dentales (por ejemplo: coronas, implantes), y la alúmina reforzada con circona (ZTA), que es el estándar actual en ortopedia para la fabricación de componentes cerámicos estructurales. Por lo tanto, este trabajo se puede dividir en dos partes principales. En la primera parte, se llevó a cabo un amplio estudio del ataque de la circona con ácido fluorhídrico (HF). Se demostró que ajustando el tiempo de decapado es posible controlar la rugosidad y la dimensión fractal de la superficie. Además, los resultados indican condiciones adecuadas para incrementar la rugosidad de forma rápida y uniforme, sin comprometer su resistencia mecánica ni tampoco su resistencia al envejecimiento. Basándose en estos hallazgos, se obtuvieron muestras con gradientes de rugosidad mediante inmersión con una velocidad controlada en una solución de ataque. Gracias a este método, que reduce drásticamente los esfuerzos y recursos necesarios para estudiar las interacciones célula-superficie, se realizó un análisis rápido de la influencia de la micro- y nano-topografía inducida por HF en las células madre mesenquimales. Se determinaron correlaciones entre parámetros de rugosidad y morfología celular, destacando la importancia de la optimización de la topografía a múltiples escalas para inducir la respuesta celular deseada. En la segunda parte, una estrategia integrada fue desarrollada para proporcionar propiedades antibacterianas y osteointegrativas a las superficies de ZTA La micro-topografía se controló mediante moldeo por inyección. Mientras tanto, un nuevo procedimiento que implica la disolución selectiva de la circona por HF (ataque selectivo) se utilizó para producir nano-rugosidad y una nanoporosidad superficial interconectada. La utilización potencial de la porosidad para la liberación de antibióticos fue demostrada, y se evidenció que la encapsulación liposomal puede aumentar la cantidad de fármaco cargada. Además, se demostró que el impacto del ataque selectivo sobre las propiedades mecánicas y la estabilidad hidrotermal era limitado. Por lo tanto, la combinación del moldeo por inyección y del ataque selectivo parece prometedora para la fabricación de componentes de ZTA implantables en contacto directo con el huesoDue to their outstanding mechanical properties and excellent biocompatibility, the use of zirconia-based ceramics in dental and orthopedic applications has grown rapidly over the last decades. However, both alumina and zirconia are bioinert, which hampers their implantation in direct contact with bone. Furthermore, infections remain one of the leading causes of implant failure. To address both issues, an improved surface design is required: in particular, an adequate topography can promote osseointegration and limit bacterial adhesion. On the other hand, long-term reliability is a major concern for load-bearing implants, and zirconia-containing ceramics require special attention. As for other ceramics, surface alterations can impair their mechanical properties. Besides, the tetragonal to monoclinic phase transformation, which accounts for their exceptional toughness, can occur spontaneously in the presence of water, potentially deteriorating the material properties. The kinetics of this phenomenon, known as hydrothermal ageing, are highly sensitive to processing changes. Any surface modification of zirconia-containing ceramics should thus be accompanied by a careful assessment of its impact on implant reliability. Based on these observations, the objective of this thesis was to develop processes to modify the surface of zirconia-based implants, in particular the topography, without compromising their mechanical properties and hydrothermal stability. The research effort focused on two materials of particular interest: yttria-stabilized zirconia (3Y-TZP), which is increasingly used for prosthodontic applications (e.g., crowns, implants), and zirconia toughened alumina (ZTA), which is the current gold Standard in orthopedics for the fabrication of load-bearing ceramic components. Accordingly, this work can be divided into two main parts. In the first part, an extensive study of the hydrofluoric acid (HF) etching of zirconia was carried out. It was shown that monitoring etching time allows controlling the roughness and fractal dimension of the surface. Furthermore, the results indicated suitable processing conditions for a fast and uniform roughening of zirconia components, without compromising substantially their strength and ageing resistance. Based on these findings, zirconia samples with roughness gradients were obtained by immersing specimens into an etching solution with a controlled speed. Thanks to this method, which drastically reduces the efforts and resources necessary to study cell-surface interactions, a rapid screening of the influence of HF-induced micro- and nano-topography on mesenchymal stem cell morphology was conducted. Correlations between roughness parameters and cell morphology were evidenced, highlighting the importance of multiscale optimization of topography to induce the desired cell response. In the second part, an integrated strategy was developed to provide both osseointegrative and antibacterial properties to ZTA surfaces. The micro-topography was controlled by injection molding. Meanwhile a novel process involving the selective dissolution of zirconia by HF (selective etching) was used to produce nano-roughness and interconnected Surface nanoporosity. Potential utilization of the porosity for delivery of antibiotic molecules was demonstrated, and it was shown that liposomal encapsulation could improve drug loading. Furthermore, the impact of selective etching on mechanical properties and hydrothermal stability was shown to be limited. The combination of injection molding and selective etching thus appears promising for fabricating a new generation of ZTA components implantable in direct contact with bone

Surface roughened zirconia: towards hydrothermal stability

Surface roughness is needed in several yttria-stabilized zirconia components used in restorative dentistry for osseointegration or adhesion purposes. This can be achieved by different treatments, which may also modify the microstructure of the surface. Among them, sandblasting and chemical etching are widely used, but their effect on hydrothermal aging of zirconia is not fully understood. In the present work, the zirconia long-term stability of rough surfaces prepared by these techniques is analyzed and a method is proposed for preventing hydrothermal aging while maintaining the original surface appearance and mechanical properties. The method involves pressure infiltration of a Cerium salt solution on the roughened surfaces followed by a thermal treatment. The solution, trapped by surface defects and small pores, is decomposed during thermal treatment into Cerium oxide, which is diffused at high temperature, obtaining Ce codoping in the near-surface region. In addition, the microstructural changes induced in the near-surface by sandblasting or chemical etching are removed by the thermal treatment together with surface defects. No color modification was observed and the final roughness parameters were in the range of existing implants of proved good osseointegration. The aging resistance of Ce co-doped materials was strongly enhanced, showing the absence of aging after artificial degradation, increasing in this way the surface mechanical integrity. The proposed treatment is easily applicable to the current manufacturing procedures of zirconia dental posts, abutments, crowns and dentures, representing a solution to hydrothermal aging in these and other biomedical applications.Peer ReviewedPostprint (author’s final draft

Hydrofluoric acid etching of dental zirconia. Part 2: effect on flexural strength and ageing behavior

Among the diverse treatments proposed to promote the osseointegration of zirconia dental implants, hydrofluoric acid (HF) etching appears to be a good candidate. However little is known on the effect of this process on the mechanical properties and long-term reliability. In this work, the surface integrity, the flexural strength and the ageing sensitivity of yttria-stabilized zirconia were assessed after etching in HF 40%. Results show that etching induces an increase of monoclinic phase content and a decrease in flexural strength. The strength decrease is limited to 15% for etching times below 60 min, whereas it reaches 29% after 120 min because of the formation of large etching pits. No substantial change in the ageing sensitivity was evidenced. Within the limits of this study, HF 40% etched zirconia appears to be reliable for long-term implantation provided that the etching duration does not exceed 60 mm. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author's final draft

Vaporisation des métaux lourds pendant l incinération des déchets ménagers (cinétiques et processus de transfert)

L objectif de cette étude est de déterminer les cinétiques de vaporisation de trois métaux (cadmium, plomb et zinc) à partir de déchets modèles proches des déchets réels. La méthodologie adoptée est basée sur une méthode inverse d identification des cinétiques de vaporisation, c est-à-dire en interprétant un signal de sortie (concentration en ML) grâce à un modèle décrivant l évolution du système. Une méthode originale d analyse en ligne des métaux lourds en phase gaz a été mise en œuvre. Un protocole de mesure adapté à nos moyens expérimentaux est déterminé à partir d une étude approfondie de la problématique de l analyse et de l étalonnage par spectrométrie ICP. La méthode proposée est ensuite validée par une expérience spécifique. Les différents essais, réalisés à vitesse de chauffe rapide (lit fluidisé) et lente (réacteur à lit fixe), montrent l influence de la température, de la teneur initiale en métal, de la nature de la matrice, de l atmosphère de combustion ou encore des phénomènes de diffusion interne sur la dynamique de vaporisation des métaux lourds. Les cinétiques de vaporisation des trois métaux étudiés sont déterminées à partir des résultats de l analyse en ligne. Les lois cinétiques théoriques sont obtenues par identification mathématique et sont validées par confrontation avec les cinétiques expérimentales. Un modèle local de la vaporisation des métaux lourds lors de la combustion d une particule d ordure ménagère a été développé. L ensemble des processus de transfert de chaleur et de masse intervenant lors de la combustion est pris en compte. Une étude paramétrique (température, géométrie de la particule, transfert de l oxygène ) démontre que le modèle décrit correctement les phénomènes physiques mis en jeu. L exploitation des simulations met en évidence l influence de la température sur le régime de contrôle de la vitesse globale de vaporisation des métaux.The main objective of this study is to determinate the vaporisation kinetics of three heavy metal (cadmium, lead and zinc) from realistic artificial wastes (derived from real wastes). A global method was used to identify the kinetics of vaporisation of heavy metals from the on-line analysis of exhaust gas. A method was developed for on-line analysis of vaporised metal in any exhaust gas by coupling an ICP (Inductively Coupled Plasma) spectrometer to the gas outlet of a laboratory fluidised bed reactor. A calibration device was set up and implemented and a standard gas synthesis protocol was developed to obtain quantitative data. The experimental study, carried out in both a fluidised bed (fast heating rate) and a fixed bed (slow heating rate), addresses the influence of temperature, initial concentration, support matrix, composition of the gas and intern diffusion on vaporisation dynamics. The kinetic laws were obtained by identifying on-line results to mathematical laws and validated by comparison to experimental kinetics. A mathematical model was developed at the particle scale in order to simulate the heavy metal vaporisation during waste combustion. It takes into account the thermal transfer phenomena, the mass transfer and the chemical reactions. This model permit to understand the influence of parameters on the kinetic control of heavy metal vaporisation.PERPIGNAN-BU Sciences (661362101) / SudocSudocFranceF

Hydrofluoric acid etching of dental zirconia. Part 2: effect on flexural strength and ageing behavior

Among the diverse treatments proposed to promote the osseointegration of zirconia dental implants, hydrofluoric acid (HF) etching appears to be a good candidate. However little is known on the effect of this process on the mechanical properties and long-term reliability. In this work, the surface integrity, the flexural strength and the ageing sensitivity of yttria-stabilized zirconia were assessed after etching in HF 40%. Results show that etching induces an increase of monoclinic phase content and a decrease in flexural strength. The strength decrease is limited to 15% for etching times below 60 min, whereas it reaches 29% after 120 min because of the formation of large etching pits. No substantial change in the ageing sensitivity was evidenced. Within the limits of this study, HF 40% etched zirconia appears to be reliable for long-term implantation provided that the etching duration does not exceed 60 mm. (C) 2015 Elsevier Ltd. All rights reserved.Peer Reviewe

On the Yttrium Tantalate – Zirconia phase diagram

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Surface roughened zirconia: towards hydrothermal stability

Surface roughness is needed in several yttria-stabilized zirconia components used in restorative dentistry for osseointegration or adhesion purposes. This can be achieved by different treatments, which may also modify the microstructure of the surface. Among them, sandblasting and chemical etching are widely used, but their effect on hydrothermal aging of zirconia is not fully understood. In the present work, the zirconia long-term stability of rough surfaces prepared by these techniques is analyzed and a method is proposed for preventing hydrothermal aging while maintaining the original surface appearance and mechanical properties. The method involves pressure infiltration of a Cerium salt solution on the roughened surfaces followed by a thermal treatment. The solution, trapped by surface defects and small pores, is decomposed during thermal treatment into Cerium oxide, which is diffused at high temperature, obtaining Ce codoping in the near-surface region. In addition, the microstructural changes induced in the near-surface by sandblasting or chemical etching are removed by the thermal treatment together with surface defects. No color modification was observed and the final roughness parameters were in the range of existing implants of proved good osseointegration. The aging resistance of Ce co-doped materials was strongly enhanced, showing the absence of aging after artificial degradation, increasing in this way the surface mechanical integrity. The proposed treatment is easily applicable to the current manufacturing procedures of zirconia dental posts, abutments, crowns and dentures, representing a solution to hydrothermal aging in these and other biomedical applications.Peer Reviewe

Local CFD kinetic model of cadmium vaporization during fluid bed incineration of municipal solid waste

The emissions of heavy metals during incineration of Municipal Solid Waste (MSW) are a major issue to health and the environment. It is then necessary to well quantify these emissions in order to accomplish an adequate control and prevent the heavy metals from leaving the stacks. In this study the kinetic behavior of Cadmium during Fluidized Bed Incineration (FBI) of artificial MSW pellets, for bed temperatures ranging from 923 to 1073 K, was modeled. FLUENT 12.1.4 was used as the modeling framework for the simulations and implemented together with a complete set of user-defined functions (UDFs). The CFD model combines the combustion of a single solid waste particle with heavy metal (HM) vaporization from the burning particle, and it takes also into account both pyrolysis and volatiles? combustion. A kinetic rate law for the Cd release, derived from the CFD thermal analysis of the combusting particle, is proposed. The simulation results are compared with experimental data obtained in a lab-scale fluidized bed incinerator reported in literature, and with the predicted values from a particulate non-isothermal model, formerly developed by the authors. The comparison shows that the proposed CFD model represents very well the evolution of the HM release for the considered range of bed temperature.Fil: Soria, Jose Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación y Desarrollo En Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Centre National de la Recherche Scientifique; Francia. Universidad Nacional del Comahue. Facultad de Ingeniería; ArgentinaFil: Gauthier, Daniel. Centre National de la Recherche Scientifique; FranciaFil: Falcoz, Quentin. Centre National de la Recherche Scientifique; FranciaFil: Flamant, Gilles. Centre National de la Recherche Scientifique; FranciaFil: Mazza, German Delfor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación y Desarrollo En Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentin

Connecting with young offenders A case study of careers work with YJT clients

SIGLEAvailable from British Library Document Supply Centre-DSC:m01/12541 / BLDSC - British Library Document Supply CentreGBUnited Kingdo