An approach to design new coatings for biomedical applications

Ti6Al4V alloy is widely used as implants for orthopedic and dental applications because of its superior mechanical properties, excellent corrosion resistance and good biocompatibility. However, it takes long period of several months for Ti6Al4V implants to integrate with the bone tissue due to their bio-inert feature in nature. An innovating and incipient method to solve the above mentioned drawbacks consist of the development of new coatings which could improve both the biological and corrosion protection performance of the Ti6Al4V alloy. Thus, a variety of strategies have been implemented to modify the surface of Ti6Al4V-based implants and enhance bone growth and their initial stability. A common approach is the deposition of bioactive hybrid coatings including inorganic and organic units on the surface of the Ti6Al4V alloy via sol-gel method. The sol–gel route is of great interest as it offers the possibility of tailoring the material properties by variation of the relative composition of the precursors used. The aim of this thesis is focused on the development of new coatings, starting with inorganic hydroxyapatite (HAp) deposited onto Ti6Al4V substrate prepared through solgel route. The effect of thermal treatment temperature on both in-vitro bioactivity and corrosion performance has been studied in simulated body fluid solution (SBF). A complete physical-chemical characterization was done in all the thermally treated coatings obtained. In-vitro tests in SBF were carried out in order to investigate the biological performance of the films. Due to the high temperature required for synthesizing HAp in crystalline form, porous and cracked coatings have been obtained, as a result of the thermal treatments applied to the prepared coatings. Although of these cracks, on the film was produced the precipitation of bone-like apatite after immersion in SBF. These precipitation products lead also to an improvement of the corrosion performance through blocking effect. The corrosion protection of the coating depends on its ability to act as a physical barrier preventing the penetration of corrosive species to reach the metal surface. This fact stimulated us to reach other goals through the preparation of sets of various new organic-inorganic hybrids. These new coatings have been also prepared through sol-gel route. To obtain workable films and their optimum preparation conditions, a new study has been carried out. The aim of this new study has been to optimize the organic– inorganic hybrid preparation method through studying the structural changes which take place during the hydrolysis and condensation processes of a mixture of γ- methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS) in solution after the addition of water and ethanol. FTIR, liquid-state ²⁹Si and ¹³C nuclear magnetic resonance (NMR) have been applied for this purpose. The results indicated that, the hydrolysis process of the two silane precursors is a time-dependent process and four hours of reaction are required for obtaining workable films. Then, after the results obtained in the first two stages of this PhD thesis, three different organic-inorganic hybrid coatings have been prepared. These coatings have been based on the MAPTMS/TMOS matrix modified with different phosphorous precursors; HAp as solid phosphorus precursor and triethylphosphite (TEP) and dimethylsilylphosphite (DMTSP) as liquid phosphorus precursors. These precursors have been added in different amounts with the aim to obtain new materials of physicalchemical and biological interest. At this level, during investigation, the following four aspects have been taken into account: 1. Evaluation of the effect of the addition of the different phosphorous precursors on the densification of the siloxane network. 2. Physical-chemical characterization of the resulting coatings. 3. Evaluation of the in-vitro osteointegration of the coatings through assays of normal human osteoblast cytotoxicity and adhesion. 4. Evaluation of the corrosion performance of the coatings. The results obtained along this study have shown that, all the prepared coatings are relatively hydrophobic with respect to the un-coated alloy. All the modified films are denser than the control one based on the MAPTMS/TMOS matrix. This fact allows these coatings to act as effective physical barriers against corrosion. The presence of phosphorus precursors results in further cross-linking and at the same time act as binding sites for protein adsorption. The importance of phosphorus in cell division and proliferation make also these coatings bioactive. The coating based on MAPTMS/TMOS/DMTSP showed the best biological performance in terms of cell proliferation and adhesion. Concerning the barrier properties provided by the designed hybrid films, the sol-gel films obtained by the chemical modification of the MAPTMS/TMOS matrix with TEP, showed the best barrier properties when immersed in SBF for 30 days. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Las aleaciones de Ti6Al4V son ampliamente utilizadas como biomaterial metálico para prótesis e implantes dentales debido a sus buenas propiedades mecánicas, excelente resistencia a la corrosión y buena biocompatibilidad. Sin embargo, son necesarios varios meses para una buena osteointegración debido a la naturaleza inerte de la aleación. Un método innovador para solucionar esta desventaja consiste en el desarrollo de nuevos recubrimientos que confieran bioactividad a la superficie de la aleación Ti6Al4V a la vez que mejoran su resistencia a la corrosión. Por esta razón, distintos tipos de estrategias se han desarrollado estos últimos años para modificar la superficie de los implantes fabricados a partir de la aleación Ti6Al4V. Todas ellas tienen como objetivo principal mejorar la interfase implante-hueso activando la formación de tejido óseo y mejorando su estabilidad en la fase inicial se osteointegración. Uno de los mejores métodos para conseguir estas interfases se basa en la aplicación de recubrimientos bioactivos sobre la superficie de la aleación. Concretamente, mediante el método sol-gel se pueden obtener recubrimientos bioactivos híbridos órgano-inorgánicos sobre la superficie de la aleación. El método sol-gel es de gran interés para la obtención de este tipo de recubrimientos porque ofrece la posibilidad de diseñar a medida las propiedades del material y/o recubrimiento deseado mediante la variación de la composición relativa de los precursores utilizados. El objetivo principal de esta tesis se centra en el desarrollo de nuevos recubrimientos multifuncionales con buenas propiedades bioactivas y anticorrosivas. El procedimiento seguido para la consecución del objetivo principal ha consistido en varias etapas. La primera ha sido partir de la síntesis de un material de bioactividad conocida, Hidroxiapatita (HAp), y optimizar los parámetros del proceso sol-gel para conseguir las mejores propiedades bioactivas tanto en forma de nanopartículas como aplicado como recubrimiento inorgánico sobre la superficie de la aleación Ti6Al4V. Para ello, se ha estudiado el efecto de la temperatura de tratamiento tanto en la respuesta bioactiva de las nanoparticulas de HAp, como en la bioactividad y la resistencia a la corrosión del recubrimiento inorgánico de HAp sobre la aleación. La respuesta bioactiva in-vitro y la resistencia a la corrosión se han estudiado en presencia de fluido fisiológico simulado (SBF). Se han obtenido nanopartículas de HAp con una excelente bioactividad. En el caso de los recubrimientos inorgánicos de HAp, debido a las altas temperaturas para conseguir la forma cristalina de la HAp, se generaron algunas grietas en los recubrimientos. A pesar de ello, en la evaluación de bioactividad mostraron precipitación de apatita con estructura similar a la ósea. Dicha precipitación también contribuyó a mejorar el efecto barrera del recubrimiento, mediante el bloqueo de poros y grietas, evitando así la incorporación de iones tóxicos provenientes de la superficie de la aleación al fluido fisiológico. La protección frente a la corrosión de un recubrimiento depende, en parte, de su habilidad para actuar como barrera evitando el acceso de especies corrosivas a la superficie metálica. Este hecho pone de manifiesto la necesidad de desarrollar otro tipo de recubrimientos, actuando como estimulo para la consecución de los siguientes objetivos de esta tesis. De esta forma, partiendo de los resultados obtenidos en la primera etapa con los recubrimientos inorgánicos de HAp, posteriormente, se ha ido aumentando la complejidad de los nuevos recubrimientos desarrollados hasta alcanzar los objetivos propuestos, bioactividad y resistencia a la corrosión. Con el fin de obtener nuevos recubrimientos viables, así como sus optimas condiciones de preparación, primeramente se desarrollo un nuevo estudio cuyo objetivo concreto ha sido la optimización del método de preparación de un nuevo recubrimiento hibrido órgano-inorgánico mediante el estudio de los cambios estructurales que tienen lugar durante los procesos de hidrólisis y condensación de una mezcla de γ- metacriloxipropiltrimetoxisilano (MAPTMS) y tetrametilortosilicato (TMOS) en solución después de la adición de agua y etanol. Este estudio se realizo mediante Espectroscopia Infraroja (IR) y Resonancia Magnetico-Nuclear (RMN) del ²⁹Si y ¹³C en estado líquido. Los resultados indicaron que la hidrólisis de estos dos precursores es un proceso dependiente del tiempo y cuatro horas de reacción es el tiempo optimo para obtener recubrimientos viables de ser aplicados y posteriormente poder actuar como matriz hibrida de recubrimientos más complejos. Tras los resultados obtenidos en estas dos primeras etapas descritas, se han diseñado y obtenido tres nuevos recubrimientos híbridos órgano-inorgánico con las propiedades requeridas. Dichos recubrimientos se basan en una matriz de MAPTMS/TMOS que ha sido modificada con distintos precursores de fósforo para dotarles de la deseada bioactividad. Los precursores de fósforo utilizados han sido nanoparticulas de HAp, como precursor sólido de fósforo y trietilfosfito (TEP) y dimetilsililfosfito (DMTSP) como precursores líquidos de fósforo. Estos precursores se han añadido en distintas cantidades con el objetivo de obtener nuevos recubrimientos de interés físico, químico y biológico. En esta etapa, durante la investigación, se han tenido en cuenta los siguientes aspectos: 1. Evaluación del efecto de la adición de los diferentes precursores de fósforo en la densificación de la matriz siloxánica. 2. Caracterización físico-química de los recubrimientos obtenidos. 3. Evaluación in-vitro de la osteointegración a partir de ensayos de citotoxicidad y adhesión de osteoblastos humanos. 4. Evaluación del comportamiento frente a la corrosión de los recubrimientos. Los principales resultados obtenidos a lo largo de este estudio han demostrado que todos los recubrimientos preparados tienen un comportamiento ligeramente más hidrofóbico que la superficie de la aleación Ti6Al4V. Todos los recubrimientos modificados con los distintos precursores de fósforo tienen mayor densidad que la matriz MAPTMS/TMOS de partida. Este hecho les confiere a estos recubrimientos unas buenas propiedades para actuar como una barrera física efectiva entre la superficie de la aleación y el medio fisiológico, mejorando así su comportamiento frente a la corrosión. La presencia de los precursores de fosforo en estado liquido, ha resultado en un aumento del grado de entrecruzamiento creando al mismo tiempo el fósforo sitios activos preferentes para la adsorción de proteínas. La importancia del fósforo en la división y proliferación celular confiere a su vez a estos recubrimientos bioactividad. De todos los recubrimientos obtenidos y estudiados, el recubrimiento basado en MAPTMS/TMOS/DMTSP mostró la mejor respuesta biológica en términos de proliferación y adhesión de osteoblastos. En relación con las propiedades barrera ofrecidas por los recubrimientos diseñados, el recubrimiento obtenido mediante modificación química con TEP de la matriz MAPTMS/TMOS de partida ha sido el que mejores propiedades barrera ha mostrado durante 30 días de inmersión en SBF

Multifunctional sol-gel derived thin film based on nanocrystaline hydroxyapatite powders

The aim of this work was to prepare bioactive hydroxyapatite coatings by sol-gel method and to study the effect of thermal treatment temperature upon the bioactivity and corrosion protection of these coatings on Ti6Al4V alloy. The application of (DTA/TGA) and (XRD) has provided valuable information about the phase transformation, mass loss, identification of the phases developed, crystallite size and degree of crystallinity. (SEM/EDX) has been applied to study the surface morphology of coated samples before and after immersion in simulated body fluid (SBF) to detect the biomimetic precipitation of the bonelike apatite. The obtained results show that all the prepared samples are ceramic nanocrystalline with crystal structure and composition like hydroxyapatite, with little deviations from that present in the human bone. The bioactivity of the studied samples is found to be closely related to the thermal treatments applied. That is, the bioactivity decreases as the temperature of the thermal treatment increase. Coatings from such prepared hydroxyapatite sol have been accomplished by dip-coating technique on non-toxic Ti6Al4V alloy for biomedical applications. The corrosion behaviour of the resulting hydroxyapatite coatings in a (SBF) has been studied by electrochemical impedance spectroscopy (EIS). The hydroxyapatite coated Ti6Al4V alloy displayed excellent bioactivity when soaked in the (SBF) and acceptable corrosion protection behaviour.This work has been supported by the National Program for Materials, Spanish Ministry of Science and Innovation (Project MAT2006-04486). A.A. El hadad acknowledges a pre-doctoral contract JAE financed by CSIC; V. Barranco acknowledges a Ramon y Cajal researcher contract financed by CSIC-MICIN

Preparation of sol-gel hybrid materials from gamma-methacryloxypropyltrimethoxysilane and tetramethyl orthosilicate: study of the hydrolysis and condensation reactions

Organic-inorganic hybrid materials suitable for the development of sol&-gel coatings for metallic surfaces were prepared by hydrolysis and condensation of gamma-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethyl orthosilicate (TMOS). The hydrolysis of MAPTMS/TMOS was carried out in an ethanol/water solution. The prehydrolysis stage of MAPTMS/TMOS system was monitored by Fourier transform infrared spectroscopy (FTIR) and liquid-state 29Si and 13C nuclear magnetic resonance (29Si and 13C NMR). FTIR analysis indicated that the hydrolysis of MAPTMS/TMOS was accomplished as far as the (SiOMe) band corresponding to unhydrolyzed silane disappeared. The concentration of the alkoxy groups and the extent of self-condensation of mono-, di-, and trisubstituted siloxanes (T species) in the sol were estimated by using liquid-state 29Si NMR spectroscopy. The hydrolysis of the prepared sol was also evaluated by liquid-state 13C NMR spectroscopy. The results indicated that under the adopted synthesis strategy conditions, the hydrolysis process requires 4 h to be completed.This work has been supported by the Ministry of Science and Innovation of Spain (Projects MAT2006-04486 and MAT2009-13530) and the Regional Community of Madrid (Project 2009/MAT-1585). AA El hadad acknowledges a predoctoral contract JAE financed by CSIC, and VB acknowledges a Ramon y Cajal researcher contract financed by CSIC-MICIN

Native Oxide Films on AZ31 and AZ61 Commercial Magnesium Alloys – Corrosion Behaviour, Effect on Isothermal Oxidation and Sol–gel Thin Film Formation

The authors present a review of their recent research work in an endeavour to interpret the influence of native oxide films on the corrosion behaviour of commercial AZ31 and AZ61 magnesium alloys or on the oxidation kinetics in air at 200°C. The tendency of some of these thin films to be sufficiently protective in mild or weak corrosive environments is examined. For obtaining oxide films with different protective properties, some of the specimens are tested with the surface in the as-received condition, while others are tested immediately after mechanical polishing. The technique applied to characterise thin (thickness of just a few nanometres) oxide films present on the surface of alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Oxidation resistance of the alloys is quantified by thermo gravimetric (TG) curves and their corrosion rate is evaluated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement in chloride solutions with different aggressivity. Emphasis is placed on the possible effects of: (a) the different thickness of the native oxide films formed on the polished surfaces on the corrosion behaviour of the alloys; and (b) the different film homogeneity and uniformity on the oxidation results. Finally, an attempt will be made to learn more about the influence of the native oxide films that cover the substrate on the subsequent growth and protective behaviour of the sol–gel coatings

Biocompatibility and corrosion protection behaviour of hydroxyapatite sol-gel-derived coatings on Ti6Al4V alloy

-2,5-diphenyl tetrazolium bromide (MTT) and Alamar blue cell viability assays were used to study the biocompatibility. Finally, the corrosion behaviour of HAp-coatings/Ti6Al4V system was researched by means of Electrochemical Impedance Spectroscopy (EIS). The obtained results showed that the prepared powders were nanocrystalline HAp with little deviations from that present in the human bone. All the prepared HAp coatings deposited on Ti6Al4V showed well-behaved biocompatibility, good bioactivity and corrosion protection properties.The authors would like to acknowledge financial support from the Ministry of Economy and Competitiveness of Spain (MAT2012-30854 and MAT2015-65445-C2-1-R Projects)

Effect of Native Oxide Film on Commercial Magnesium Alloys Substrates and Carbonate Conversion Coating Growth and Corrosion Resistance

Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 solution treatment and the enhancement of corrosion resistance have been studied. The significant increase in the amount of aluminum and carbonate compounds on the surface of the conversion coating formed on the AZ61 substrate in polished condition seems to improve the corrosion resistance in low chloride ion concentration solutions. In contrast, the conversion coatings formed on the AZ31 substrates in polished condition has little effect on their protective properties compared to the respective as-received surfacefinancial support for this work from the Ministry of Economy and Competitivity of Spain (MAT 2009-13530 and MAT2012-30854)We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)Peer reviewe

Influence of substrate composition on corrosion protection of sol-gel thin films on magnesium alloys in 0.6 M NaCl aqueous solution

The corrosion protection behaviour of organic–inorganic hybrid thin films on AZ31 and AZ61 magnesium alloy substrates has been studied. These films were prepared by a sol–gel dip-coating method. The organopolysiloxane precursors were γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethoxysilane (TMOS). An attempt was made to determine the possible relationships between the degradation of the sol–gel film and composition of the metal substrate during the exposure of the metal/coating system to 0.6 M NaCl aqueous solutions. For this purpose electrochemical impedance spectroscopy (EIS) and hydrogen evolution measurements were applied. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the sol–gel films formed on the surface of AZ61 alloy were far more perfect and uniform than those formed on the AZ31 alloy. This behaviour was attributed to the effect of the native oxide film initially present on the surface of the AZ61 alloy, which inhibited the attack of magnesium. Results indicated that the sol–gel coated AZ61 substrate tended to develop corrosion products slower than the sol–gel coated AZ31 substrate, trend that could change by prolonging exposure time. After 6 days of immersion, a clear inhibitive effect of the corrosion products formed during the test was observed in the case of the sol–gel coated AZ31, but not with the coated AZ61 alloy substrate, a phenomenon explained by the carbonate enrichment observed by XPSfinancial support for this work from the Ministry of Economy and Competitivity of Spain (MAT 2009-13530 and MAT2012-30854). A.A. El Hadad acknowledges a pre-doctoral contract JAE financed by CSIC. V.B. acknowledges a Ramon y Cajal researcher contract financed by CSIC and MINECOPeer reviewe

Kinetics of the Thermal Degradation of Granulated Scrap Tyres: a Model-free Analysis

<p>Pyrolysis is a technology with a promising future in the recycling of scrap tyres. This paper determines the thermal decomposition behaviour and kinetics of granulated scrap tyres (GST) by examining the thermogravimetric/derivative thermogravimetric (TGA/DTG) data obtained during their pyrolysis in an inert atmosphere at different heating rates. The model-free methods of Friedman, Flynn-Wall-Ozawa and Coats-Redfern were used to determine the reaction kinetics from the DTG data. The apparent activation energy and pre-exponential factor for the degradation of GST were calculated. A comparison with the results obtained by other authors was made.</p><p>DOI: <a href="http://dx.doi.org/10.5755/j01.ms.19.4.2947">http://dx.doi.org/10.5755/j01.ms.19.4.2947</a></p

Multifunctional sol-gel derived thin film based on nanocrystaline hydroxyapatite powders

The aim of this work was to prepare bioactive hydroxyapatite coatings by sol-gel method and to study the effect of thermal treatment temperature upon the bioactivity and corrosion protection of these coatings on Ti6Al4V alloy. The application of (DTA/TGA) and (XRD) has provided valuable information about the phase transformation, mass loss, identification of the phases developed, crystallite size and degree of crystallinity. (SEM/EDX) has been applied to study the surface morphology of coated samples before and after immersion in simulated body fluid (SBF) to detect the biomimetic precipitation of the bonelike apatite. The obtained results show that all the prepared samples are ceramic nanocrystalline with crystal structure and composition like hydroxyapatite, with little deviations from that present in the human bone. The bioactivity of the studied samples is found to be closely related to the thermal treatments applied. That is, the bioactivity decreases as the temperature of the thermal treatment increase. Coatings from such prepared hydroxyapatite sol have been accomplished by dip-coating technique on non-toxic Ti6Al4V alloy for biomedical applications. The corrosion behaviour of the resulting hydroxyapatite coatings in a (SBF) has been studied by electrochemical impedance spectroscopy (EIS). The hydroxyapatite coated Ti6Al4V alloy displayed excellent bioactivity when soaked in the (SBF) and acceptable corrosion protection behaviour.Peer Reviewe

Study of the biocompatibility and corrosion resistance of hydroxyapatite Sol-Gel thin coatings on Ti6Al4V alloy

Oral presentation given at the PRiME 2016, held in Honolulu (Hawaii) on October 2-7th, 2016.The aim of this work was to prepare hydroxyapatite thin films (HAp) by a sol-gel method and to study the effect of thermal treatment temperature upon the biocompatibility and corrosion protection of these coatings on Ti6Al4V alloy. The HAp sol was obtained by hydrolysis and condensation of a mixture of triethyl phosphite and calcium nitrate tetrahydrate in stoichiometric amounts (i.e. maintaining a Ca/P ratio of 1.67) adapting a water-based route. The crystallite size and degree of crystallinity of the HAp sol-gel derived coatings strongly depends on the thermal treatment applied. Based on this knowledge, the HAp sol-gel films were annealing in air during 2h at 400ºC, 600ºC, 800ºC and 1200ºC, respectively. As an alternative to conventional thermal treatments, a set of samples was prepared by applying a modification of the Controlled Rate Thermal Analysis (CRTA) developed by Rouquerol, with the aim of obtaining HAp ceramic thin films with controlled textural characteristics at lower temperatures. The basis of this thermal treatment is to control temperature and pressure system, keeping constant the decomposition speed. The application of Thermogravimetric/Differential Thermal Analyses (TG/DTA) and X-ray Diffraction (XRD) has provided valuable information about the phase transformation, mass loss, identification of the phases developed, crystallite size and degree of crystallinity of the obtained HAp powders. Fourier Transformer Infrared Spectroscopy (FTIR) has been utilized for studying the functional groups within the prepared structures. The surface morphology and nature of the prepared HAp coatings was studied by Scanning Electron Microscopy (SEM) with energy dispersive spectroscopy (EDS). The specific surface (BET) and porosity of the material were determined starting from isotherms of adsorption for N2 at a temperature of 77 K. The corrosion protection behaviour of the HAp-coatings/Ti6Al4V in Kokubo¿s Simulated Body Fluid (SBF) has been studied by Electrochemical Impedance Spectroscopy (EIS). Inductively Coupled Plasma (ICP) has been used to detect the concentration of Ca2+ and PO43- ions released and re-precipitated upon the HAp coatings submitted to soaking test in SBF. The quantification of the in vitro cytotoxicity of the HAp sol-gel coatings was made with human osteoblast cultures and a tetrazolium dye (MTT) based assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide)). Finally the analysis of the adhesion and cellular proliferation on the surface of the materials was also carried out. In these last studies Alamar Blue assays and human osteoblast cultures have been used. In summary hydroxyapatite nano-crystalline coatings on Ti6Al4V alloy have been obtained by a water-based sol-gel route. The crystallite size and degree of crystallinity of the HAp sol-gel derived coatings strongly depends on the thermal treatment applied. HAp films have been successfully obtained by annealing sol-gel-derived coatings in air during 2h at 600ºC and 800ºC. As an alternative to these conventional thermal treatments it has been possible to crystallize pure hydroxyapatite at 100°C of temperature of control for the pressure and 300°C as maximum temperature by applying controlled rate thermal analysis (CRTA) conditions. The obtained results have shown that the prepared coatings are nanocrystalline HAp with little deviations from that present in the human bone. All these HAp coating/Ti6Al4V systems have shown to have good bioactivity upon immersion in SBF, good biocompatibility and corrosion protection properties.The authors would also like to acknowledge the Ministerio de Economía y Competitividad of Spain (Projects MAT2012-38541-C02-02 and MAT2015-65445-C2-1-R) and Comunidad de Madrid (Project S2013/MIT-2862-MULTIMAT-CHALLENGE) for funding this research