Publication: Development and characterization of advanced thin coatings on nanostructured titanium for biomedical applications
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2020-01
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2020-02-07
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Abstract
El titanio comercialmente puro nanoestructurado, o de grano fino (UFG CP Ti, por sus siglas en inglés), ha surgido como uno de los mejores candidatos para su aplicación en la fabricación de implantes debido a su biocompatibilidad, superior a la del resto de materiales metálicos utilizados en el campo de la biomedicina, y por las mejora en las propiedades mecánicas que confiere microestructura de grano fino que se obtiene mediante procesos de deformación plástica severa (SPD). Sin embargo, el carácter bioinerte del Titanio puro hace necesaria la búsqueda métodos para mejorar la osteoconductividad de su superficie para asegurar una rápida y exitosa integración con el hueso humano tras la implantación. Ha sido demostrado que la adhesión y proliferación celular y las capacidades osteoconductivas del Titanio puro de grano grueso y grano fino, se pueden mejorar siguiendo estrategias de modificación superficial que incluyen la utilización de métodos físicos y/o químicos para aumentar la rugosidad de la superficie y la fabricación de recubrimientos bioactivos. En particular, la técnica oxidación electrolítica asistida por plasma (PEO) resulta se erige como una de los métodos más prometedores para la fabricación de recubrimientos finos de TiO2 con altos contenidos en Ca y P. Este tipo de recubrimientos proporcionan a la superficie del titanio una combinación óptima de topografía y composición química para aplicaciones que requieren propiedades osteoconductivas. Sin embargo, existe un cierto vacío de información acerca del tratamiento mediante PEO del Titanio nanoestructurado en comparación con el amplio número de publicaciones científicas sobre recubrimientos de tipo PEO sobre Titanio de grano grueso. La presente tesis doctoral se centra en la modificación superficial del Titanio de grano grueso para mejorar su osteoconductividad. El efecto sobre la adhesión y proliferación celular de la topografía superficial producida mediante diversos ataques químicos del Titanio nanoestructurado fue estudiado durante esta tesis. Se observó que la proliferación celular dependía de las características de la topografía superficial. La parte principal de la Tesis consistió en la fabricación de recubrimientos de tipo PEO en Titanio comercialmente puro tanto de grano grueso como nanoestructurado usando tres tipos distintos de electrolito, uno de ellos con el objetivo de producir recubrimientos ricos en Ca y P. Este estudio perseguía dos objetivos: en primer lugar, comparar la resistencia a la corrosión, la interacción celular y las propiedades mecánicas conseguidas con los tres electrolitos; en segundo lugar, comparar la aplicabilidad del tratamiento PEO y los recubrimientos obtenidos en Titanio de grano grueso y nanoestructurado. Se observó que la microestructura de grano fino afectaba al ritmo de crecimiento de los recubrimientos, la generación de descargas de cada electrolito y la microestructura de las capas en contacto con el substrato. Este último efecto jugó, al mismo tiempo, un papel fundamental en el comportamiento ante la corrosión de los recubrimientos. El comportamiento mecánico de los recubrimientos dependió enormemente de la microstructura de las capas externas de los recubrimientos, por lo que solo se encontraron diferencias en cuanto al espesor. Las céluals cultivadas sobre el recubrimiento rico en Ca y P fabricado a 120 s sobre el Ti nanoestructurado demostró la mejor proliferación y actividad metabolica, indicando el potencial de este recubrimiento para presentar propiedades osteoinductivas y osteoconductivas. Con el fin de mejorar las propiedades mecánicas de los recubrimientos, se propone un método alternativo a los métodos tradicionales de endurecimiento de recubrimientos de tipo PEO.
UltraFine-Grained Commercially Pure Titanium (UFG CP Ti) has arisen as one of the best prospects for the fabrication of implantable appliances due to the superior biocompatibility of CP Ti with respect to the other metallic systems used in the biomedical field, and to the enhanced mechanical properties provided by the refined microstructure obtained through Severe Plastic Deformation (SPD) processes. However, the bioinert character of CP Ti makes necessary to improve the osteoconductivity of the surface in order to ensure a rapid and successful osseointegration. Surface modification approaches including physical and/or chemical roughening and the fabrication of bioactive coatings have been shown to improve the cell adhesion and proliferation and osteoconductivity of CG and UFG CP Ti. In particular, the Plasma Electrolytic Oxidation (PEO) technique is one of the most promising approaches to fabricate thin TiO2-based Ca- and P-containing coatings. These type of coatings provide a suitable combination of surface topography and chemistry for applications that require osteoconductive properties. However, there is a relative lack of knowledge regarding the PEO treatment of UFG CP Ti in comparison with the significant body of research on the PEO treatment of CG CP Ti. The present Thesis is focused on the surface modification of UFG CP Ti to improve its osteoconductivity. The effect of the surface topography of chemically etched UFG CP Ti on the cell adhesion and proliferation was assessed. It was observed that the cell proliferation was dependent on the characteristics of the surface topography. The main body of the Thesis consisted on the fabrication of PEO coatings on both CG and UFG CP Ti using three different electrolytes, one of them aimed to produce Ca- and P-containing coatings. The main objective of this study was twofold: First, to compare the resulting corrosion resistance, cell-surface interaction, and mechanical properties of the three PEO treatments; and second, to compare the applicability of the PEO treatment and the coatings obtained on both CG and UFG CP Ti. The UFG microstructure was found to influence the coatings growth rate, the discharge generation of each treatment and the microstructure of the layers in intimate contact with the substrate. At the same time, the latter was found to cause significant differences in the corrosion behaviour between the CG CP Ti-coated and the UFG CP Ti-coated samples. The mechanical performance of the coatings was strongly dependent on the microstructure of the outer layers of the coatings. The Ca- and P-containing coating fabricated for 120 s on the UFG CP Ti presented the highest celular proliferation rate and metabolic activity showing potential for osteoinductive and osteoconductive capabilities. In order to improve the mechanical performance of the coatings an alternative approach to the common methods for hardening of PEO coatings was proposed.
UltraFine-Grained Commercially Pure Titanium (UFG CP Ti) has arisen as one of the best prospects for the fabrication of implantable appliances due to the superior biocompatibility of CP Ti with respect to the other metallic systems used in the biomedical field, and to the enhanced mechanical properties provided by the refined microstructure obtained through Severe Plastic Deformation (SPD) processes. However, the bioinert character of CP Ti makes necessary to improve the osteoconductivity of the surface in order to ensure a rapid and successful osseointegration. Surface modification approaches including physical and/or chemical roughening and the fabrication of bioactive coatings have been shown to improve the cell adhesion and proliferation and osteoconductivity of CG and UFG CP Ti. In particular, the Plasma Electrolytic Oxidation (PEO) technique is one of the most promising approaches to fabricate thin TiO2-based Ca- and P-containing coatings. These type of coatings provide a suitable combination of surface topography and chemistry for applications that require osteoconductive properties. However, there is a relative lack of knowledge regarding the PEO treatment of UFG CP Ti in comparison with the significant body of research on the PEO treatment of CG CP Ti. The present Thesis is focused on the surface modification of UFG CP Ti to improve its osteoconductivity. The effect of the surface topography of chemically etched UFG CP Ti on the cell adhesion and proliferation was assessed. It was observed that the cell proliferation was dependent on the characteristics of the surface topography. The main body of the Thesis consisted on the fabrication of PEO coatings on both CG and UFG CP Ti using three different electrolytes, one of them aimed to produce Ca- and P-containing coatings. The main objective of this study was twofold: First, to compare the resulting corrosion resistance, cell-surface interaction, and mechanical properties of the three PEO treatments; and second, to compare the applicability of the PEO treatment and the coatings obtained on both CG and UFG CP Ti. The UFG microstructure was found to influence the coatings growth rate, the discharge generation of each treatment and the microstructure of the layers in intimate contact with the substrate. At the same time, the latter was found to cause significant differences in the corrosion behaviour between the CG CP Ti-coated and the UFG CP Ti-coated samples. The mechanical performance of the coatings was strongly dependent on the microstructure of the outer layers of the coatings. The Ca- and P-containing coating fabricated for 120 s on the UFG CP Ti presented the highest celular proliferation rate and metabolic activity showing potential for osteoinductive and osteoconductive capabilities. In order to improve the mechanical performance of the coatings an alternative approach to the common methods for hardening of PEO coatings was proposed.
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Keywords
Ultra-fine grained microstructure, Severe Plastic Deformation (SPD), Plasma Electrolytic Oxidation (PEO), Osteoconductivity, Biocompatibility, Mechanical properties, Functional properties, Titanium