Development of porous coatings enriched with magnesium and zinc obtained by DC plasma electrolytic oxidation

Coatings with developed surface stereometry, being based on a porous system, may be obtained by plasma electrolytic oxidation, PEO (micro arc oxidation, MAO). In this paper, we present novel porous coatings, which may be used, e.g., in micromachine's biocompatible sensors' housing, obtained in electrolytes containing magnesium nitrate hexahydrate Mg(NO3)(2)center dot 6H(2)O and/or zinc nitrate hexahydrate Zn(NO3)(2)center dot 6H(2)O in concentrated phosphoric acid H3PO4 (85% w/w). Complementary techniques are used for coatings' surface characterization, such as scanning electron microscopy (SEM), for surface imaging as well as for chemical semi-quantitative analysis via energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), and X-ray powder diffraction (XRD). The results have shown that increasing contents of salts (here, 250 g/L Mg(NO3)(2)center dot 6H(2)O and 250 g/L Zn(NO3)(2)center dot 6H(2)O) in electrolyte result in increasing of Mg/P and Zn/P ratios, as well as coating thickness. It was also found that by increasing the PEO voltage, the Zn/P and Mg/P ratios increase as well. In addition, the analysis of XPS spectra revealed the existence in 10 nm top of coating magnesium (Mg2+), zinc (Zn2+), titanium (Ti4+), and phosphorus compounds (PO43-, or HPO42-, or H2PO4-, or P2O74-).Web of Science97art. no. 33

Plasma Electrolytic Oxidation (PEO) Coatings

Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation (MAO), functionalizes surfaces, improving the mechanical, thermal, and corrosion performance of metallic substrates, along with other tailored properties (e.g., biocompatibility, catalysis, antibacterial response, self-lubrication, etc.). The extensive field of applications of this technique ranges from structural components, in particular, in the transport sector, to more advanced fields, such as bioengineering. The present Special Issue covers the latest advances in PEO‐coated light alloys for structural (Al, Mg) and biomedical applications (Ti, Mg), with 10 research papers and 1 review from leading research groups around the world

Electrodeposition of copper and brass coatings with olive-like structure

One method of creating a brass coating is through electrodeposition, which is most often completed in cyanide galvanic baths. Due to their toxicity, many investigations focused on the development of more environmentally friendly alternatives. The purpose of the study was to explore a new generation of non-aqueous cyanide-free baths based on 1-ethyl-3-methylimidazolium acetate ionic liquids. The study involved the formation of copper, zinc, and brass coatings. The influence of the bath composition, cathodic current density, and temperature was determined. The obtained coatings were characterized in terms of their morphology, chemical composition, phase composition, roughness, and corrosion resistance. It was found that the structure of the obtained coatings is strongly dependent on the process parameters. The three main structure types observed were as follows: fine-grained, porous, and olive-like. To the best knowledge of the authors, it is the first time the olive-like structure was observed in the case of an electrodeposited coating. The Cu-Zn coatings consisted of 19–96 at. % copper and exhibited relatively good corrosion resistance. A significant improvement of corrosion properties was found in the case of copper and brass coatings with the olive-like structure

Modern Surface Engineering Treatments

Surface engineering can be defined as an enabling technology used in a wide range of industrial activities. Surface engineering was founded by detecting surface features which destroy most of pieces, e.g. abrasion, corrosion, fatigue, and disruption; then it was recognized, more than ever, that most technological advancements are constrained with surface requirements. In a wide range of industry (such as gas and oil exploitation, mining, and manufacturing), the surfaces generate an important problem in technological advancement. Passing time shows us new interesting methods in surface engineering. These methods usually apply to enhance the surface properties, e.g. wear rate, fatigue, abrasion, and corrosion resistance. This book collects some of new methods in surface engineering

Funcionalización de superficie de aleaciones de magnesio para implantes biodegradableS

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, leída el 19-12-2022The most important challenge for tissue engineering is the design and fabrication of biomaterials that fulfil specific functions according to the needs of society. In the Introduction of this Doctoral Thesis emphasis is placed on the literature review of magnesium based biomaterials in terms of their corrosion behavior under physiological conditions similar to those of the human body. Both commercially available materials and materials under development for application in temporary orthopaedic and cardiovascular implants are reviewed. The main limitation of magnesium based alloys is their low corrosion resistance under physiological conditions leading to premature implant failure.Surface modification of temporary implants is a strategy that enables modulation of surface composition and topography as well as the implant degradation rate according to specific needs. A bibliographic study has been carried out focussing on the advances in hybrid biomaterials achieved through combination of ceramic and polymeric layers, revealing their potential for controlled drug delivery and improved biocompatibility of the implant. The literature review revealed the challenge that loaded drugs can present for the degradation rate of magnesium alloy-based implants. The inhibitory or accelerating effect of the drugs on corrosion behavior of the system is currently overlooked...El reto más importante para la ingeniería de tejidos es el diseño y fabricación de biomateriales que cumplan las funciones específicas según las necesidades de la sociedad. En la Introducción de esta Tesis Doctoral se enfatiza en la revisión bibliográfica de los biomateriales de base magnesio en términos de su comportamiento a la corrosión en condiciones fisiológicas similares a las del cuerpo humano. Se revisan tanto los materiales comercializados como los materiales en desarrollo para su aplicación en implantes temporales ortopédicos y cardiovasculares. La principal limitación de estas aleaciones de base magnesio es su baja resistencia a la corrosión en condiciones fisiológicas dando lugar a un fallo prematuro del implante. La modificación superficial de estos implantes es una estrategia interesante que permite modular la composición y la topografía de la superficie, así como la velocidad de degradación del implante según las necesidades específicas buscadas. Se ha realizado un estudio bibliográfico centrado en los avances en biomateriales híbridos mediante la combinación de capas cerámicas y poliméricas, revelando su potencial para la administración controlada de fármacos y la mejora de la biocompatibilidad del implante. La revisión bibliográfica reveló que los fármacos cargados pueden presentar un desafío para la velocidad de degradación de los implantes basados en aleaciones de magnesio. El efecto inhibidor o acelerador de los fármacos sobre el comportamiento de la corrosión del sistema es actualmente ignorado...Fac. de Ciencias QuímicasTRUEunpu

Recent Advances in Metal, Ceramic, and Metal-Ceramic Composite Films/Coatings

This reprint gathers works on various coating materials and technologies aimed at the improvement of materials’ properties, such as corrosion resistance or biocompatibility. Systematic studies demonstrate how the structure and morphology of coatings can change the mechanical, chemical and various functional properties of materials. The reprint contributes to the better understanding of various phenomena induced by metal, ceramic or composite coatings in core materials and, thus, it can help in the more rational design of the selected material’s properties in future studies by the application of coatings

Investigation of Plasma Electrolytic Oxidation of Commercially Pure Magnesium For Biomedical Applications

Permanently implanted biomaterials may cause problems to the host body associated with long term chronic inflammation which would eventually require revision surgery. The development of biodegradable materials which can be absorbed, consumed and excreted by the patient is therefore of interest. Magnesium alloys have for a long time been considered as potential biomaterials for load-bearing applications due to their excellent biological properties including superior biochemical and biomechanical compatibility compared to other alternatives such as biodegradable polymers and bioceramics. However, the application of magnesium material in the biological area is still limited due to its intrinsically poor corrosion performance in the biological environments. Therefore, various methods have been explored to control the degradation rate of magnesium in biological fluid, of which plasma electrolytic oxidation (PEO) is the most promising method. PEO is a plasma-assisted anodising process that can convert the surface of magnesium into a ceramic layer, thus preventing the corrosive medium contacting the substrate; therefore, the degradation rate can be reduced. Furthermore, highly biocompatible coatings can be produced when appropriate electrolytes are used in the PEO process. Motivated by the beneficial properties of magnesium and corrosion protection provided by the PEO technique, considerable efforts have been devoted towards the development of magnesium implants based on PEO protection. Nevertheless, the corrosion rate of magnesium has not been reduced to an acceptable level and a universal PEO process appropriate for magnesium has not yet been established. In the present study, PEO processes on commercially pure (cp) magnesium and the resulting coating characteristics have been systematically studied. Through this progressive study, a biologically friendly electrolyte containing Ca and P compounds have been developed. An appropriate current regime for this electrolyte has also been studied. Finally, a hydroxyapatite layer, intended to enhance the sample bioactivity, was deposited on the PEO coated cp magnesium. The PEO process was studied according to key electrical characteristics including voltage transient, and voltage/current waveforms. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were employed to study the surface and cross-sectional morphology, elemental composition, phase composition of the coatings. Residual stress induced by the PEO process is also studied using XRD method. The corrosion properties of the coated samples in simulated body fluid (SBF) were studied using electrochemical methods including open circuit potential (OCP) monitoring, electrochemical impedance spectroscopy (EIS) measurement, and potentiodynamic polarisation scans. The mechanical properties, including static tensile properties and cyclic fatigue performance of the coated samples were also studied to verify the applicability of magnesium in biological areas from the mechanical point of view. The results indicated that the combination of a pulsed unipolar (PUP) current regime of 3000 Hz and an electrolyte composed of 12 g/l Na3PO4•12H2O and 2g/l Ca(OH)2 provides the best process stability and success of Ca and P incorporation. Moreover, the corrosion resistance of cp magnesium in the SBF could be improved by more than 10 times. Nevertheless, such protection is very limited as the coating was degraded rapidly in the simulated body fluid, which is due to the chemical instability of MgO at the pH of SBF. Tensile and cyclic fatigue tests demonstrated that the PEO coated cp magnesium possesses sufficient mechanical properties for general load-bearing biomedical applications even though the fatigue strength is significantly deteriorated by the surface modification. Further work required to achieve better control over the biodegradation process of Mg implants can be outlined as follows: (i) robustness of the developed PEO process should be explored on other corrosion resistant magnesium alloys containing biologically friendly elements (like Ca, Zn, Mn); (ii) addition of F-, SiO32- in the electrolyte to facilitate the formation of stable compounds besides MgO in the PEO coating, thus reducing the degradation rate of magnesium based implant

Development and surface modification of β-Titanium alloys produced by powder metallurgy for biomedical applications

Mención Internacional en el título de doctorTitanium and its alloys have been widely used in biomedical applications. Ti-6Al-4V and Ti-6Al-7Nb are the most employed Ti alloys for dental and orthopaedic implants. Ti alloys are preferred over stainless steel and CrCo alloys due to their distinctive properties such as low density, high specific resistance, high corrosion resistance, especially in contact with human fluids and tissues, and biocompatibility. Despite their excellent properties, orthopaedic hip implants have three main issues, due to the alloy properties that compromise their durability. Firstly, the currently used Ti alloys have higher elastic modulus values than the bone. The mismatch between the elastic moduli of the bone (10-30 GPa) and Ti alloys (100-110 GPa) produces the stress-shielding phenomenon. In the long term, stress-shielding produces bone resorption, which causes implant loosening. Secondly, due to the low wear resistance of Ti alloys, metal ions and wear particles are released, which could have harmful local and systemic effects, and cause cell tissue damage. Finally, the lack of bioactivity of Ti limits the bone growth around the implant, affecting the bonding between both surfaces (bone and implant), until its loosening. All these problems cause the premature failure of hip implants, increasing the revision surgeries rate, since the prosthesis must be replaced earlier than expected. Therefore, suitable Ti alloys for orthopaedic applications must exhibit low elastic modulus, high wear resistance, and high bioactivity, to prevent the occurrence of these problems. This thesis attempts to cover the previous problems, pursuing the following goal: development of biocompatible and low modulus β-Ti alloys with improved wear resistance and a biofunctionalised surface to improve the interaction between the implant surface and bone tissue. β-Ti alloys were processed using Nb and Fe as alloying elements and TiH2 as Ti source. Both Fe and Nb are non-toxic and biocompatible β-stabiliser elements. Ti-Nb alloys have gained attention to produce biomedical Ti alloys, because they exhibit a lower elastic modulus. Fe alloying element reduces the Nb content necessary, and therefore the alloy cost, maintaining the β-Ti phase. Moreover, it has been reported that small Fe additions improve the Ti sinterability and mechanical properties. TiH2 is cheaper than CP-Ti, and it offers higher sinterability than elemental Ti and provides an inert atmosphere during its decomposition, which protects the particle surface during the consolidation, preventing contamination issues. Therefore, TiH2 is an attractive candidate to produce Ti-based components, while maintaining mechanical properties and reducing the processing costs. The design and development of these β-Ti alloys are described in detail in Chapter 4 and Chapter 5. The success of TiH2 use as a Ti substitute, highly depends on the dehydrogenation process, that is, how hydrogen is released when the sample is heated. Hence, this thesis includes a detailed study about the dehydrogenation process and how alloying elements (Nb and Fe) influence this process, considering the effect that they have, when they are incorporated individually and in a combination form. From this study, relevant principles were established to define the appropriate consolidation conditions that promote a controlled and complete transformation from TiH2 to Ti. The details of this study are included in Chapter 4. Wear resistance was improved following two strategies described in Chapter 6: (1) by developing Ti composite materials, incorporating TiB2 and TiN particles as ceramic reinforcements, and (2) by promoting the formation of TiN coatings obtained by nitriding treatments. Finally, surface modification was performed by micro-arc oxidation treatments, obtaining a porous layer of titanium oxide on the sample surface, which is enriched with bioactive elements (Ca and P) and antibacterial agents (ZnO) that enhance the cellular response, improve osseointegration, and prevent the bacteria proliferation. This study is included in Chapter 7. Processed samples were evaluated based on their microstructural features and mechanical properties (hardness, elastic modulus, fatigue behaviour), as well aswear resistance. Furthermore, the biocompatibility of the base alloys was studied, confirming the viability of these substrates for biomedical applications. The main results obtained establish that the low-cost β-Ti alloys developed in this work are suitable candidates for biomedical applications. They show reduced elastic modulus values and improved wear resistance. Regarding biofunctionalised surfaces, samples presented a multiscale porous structure and a high Ca/P ratio. These are promising features to promote osseointegration and mimic the implant with the bone tissue.El titanio y sus aleaciones son materiales ampliamente utilizados en aplicaciones biomédicas. Entre estas aleaciones destacan el Ti-6Al-4V y Ti-6Al-7Nb que componen la mayoría de implantes dentales y ortopédicos. El principal motivo para el uso de estos materiales frente al acero inoxidable y aleaciones CrCo responde a su combinación de propiedades, tales como baja densidad, alta resistencia específica, alta resistencia a la corrosión, especialmente en contacto con fluidos y tejidos corporales, y biocompatibilidad. Pese a sus buenas propiedades, los implantes ortopédicos de cadera presentan tres problemas principales relacionados con las propiedades del material, que comprometen la durabilidad del implante. Primero, las aleaciones de titanio más utilizadas presentan un elevado módulo de elasticidad en comparación con el hueso. La diferencia entre el módulo elástico del hueso (10-30 GPa) y el módulo elástico de las aleaciones de Ti (100-110 GPa) provoca el fenómeno conocido como “stress-shielding”. A largo plazo, el stress-shielding produce la resorción ósea, que desencadena en el aflojamiento y pérdida del implante. Segundo, debido a la baja resistencia a desgaste de las aleaciones de Ti se liberan iones metálicos y partículas de desgaste que podrían causar efectos locales, sistémicos y daños en el tejido celular. Por último, la falta de bioactividad del Ti impide el crecimiento óseo alrededor del implante, perjudicando la unión entre ambas superficies (hueso-implante). Esto podría afectar a la fijación del implante hasta producir su desprendimiento. Los problemas enumerados anteriormente están asociados al fallo prematuro de los implantes de cadera. A causa de ellos aumenta la tasa de cirugías de revisión y las prótesis deben ser reemplazadas antes de lo esperado. En consecuencia, con objeto de evitar su aparición, las aleaciones de Ti apropiadas para aplicaciones ortopédicas deben presentar bajo módulo elástico, alta resistencia al desgaste y alta bioactividad. Esta tesis aborda la problemática anterior persiguiendo el siguiente objetivo: el desarrollo de aleaciones β-Ti de bajo módulo elástico, biocompatibles, con una resistencia al desgaste mejorada y una superficie biofuncionalizada a fin de mejorar la interacción entre la superficie del implante y el tejido óseo. Las aleaciones β-Ti se procesaron utilizando Nb y Fe como elementos de la aleación y TiH2 como fuente de Ti. El Fe y el Nb son elementos estabilizadores de la fase β, no tóxicos y biocompatibles. El uso de Nb en el desarrollo de aleaciones biomédicas de Ti es de gran interés debido a la significativa reducción del módulo elástico reportado en las aleaciones Ti-Nb. El Fe, por su parte, aporta interesantes ventajas: permite disminuir el contenido de Nb, manteniendo la microestructura constituida por fase β-Ti; reduce el coste total de la aleación, al reducir el contenido de Nb; y mejora la sinterabilidad del Ti y las propiedades mecánicas. El TiH2 es más barato que el Ti. Presenta mayor sinterabilidad que el Ti elemental y provee una atmósfera inerte durante su descomposición que protege la superficie de las partículas, reduciendo la contaminación de la pieza. Por ello, se considera un candidato atractivo para producir componentes base Ti manteniendo sus propiedades mecánicas y reduciendo los costes de procesamiento. El diseño y desarrollo de estas aleaciones de β-Ti se describe en detalle en el Capítulo 4 y Capítulo 5. El proceso de deshidrogenación, es decir, cómo se libera el hidrógeno a medida que se caliente la muestra, determina, en gran medida, el éxito para sustituir el Ti por TiH2. Por ello, esta tesis incluye un estudio detallado sobre el proceso de deshidrogenación, así como la influencia de los elementos de aleación (Nb y Fe) en este proceso, evaluando su efecto al añadirse de forma individual y combinada/conjunta. Como resultado de este estudio surgieron consideraciones relevantes, empleadas para definir las condiciones más adecuadas de consolidación de las muestras, a fin de promover una transformación controlada y completa de TiH2 a Ti. Los detalles de este estudio se presentan en el Capítulo 4. Para la mejora de la resistencia al desgaste de las aleaciones β se proponen dos estrategias, descritas en el Capítulo 6: (1) desarrollar materiales compuestos incorporando partículas de TiB2 y TiN como refuerzos cerámicos; (2) producir recubrimientos de TiN mediante tratamientos de nitrurado. Finalmente, se modifica la superficie del material mediante tratamientos de “micro-arc oxidation (anodizado). Con este tratamiento se obtiene una capa porosa de óxido de titanio enriquecida con elementos bioactivos (Ca y P) y agentes antibacterianos (ZnO) que potencian la respuesta celular, mejoran la osteointegración y evitan/reducen la proliferación de bacterias. Este estudio se desarrolla en el Capítulo 7. Las muestras procesadas con las premisas anteriores se evaluaron en función de sus características microestructurales, propiedades mecánicas (dureza, módulo de elasticidad, comportamiento a fatiga), y resistencia a desgaste. Además, se estudió la biocompatibilidad de las aleaciones base que confirma la viabilidad de estos sustratos en aplicaciones biomédicas. Los resultados principales indican que las aleaciones β-Ti de bajo coste, producidas y modificadas en este trabajo son adecuadas para aplicaciones biomédicas: presentan valores de módulo elástico reducidos y mejor resistencia al desgaste. Los resultados obtenidos en las superficies biofuncionalizadas son prometedores ya que las muestras exhiben una estructura porosa multiescala y una alta relación Ca/P, útiles para mimetizar el implante con el tejido óseo y favorecer la osteointegración.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Alexandra Amherd Hidalgo.- Secretario: Carlos Romero Villarreal.- Vocal: Isabel Montealegre Melénde