825 research outputs found
Design and development of low elastic modulus Ti-Nb-Zr alloys for biomedical applications
The demand for implants has been increasing globally due to the rising population of the older people (aged ≥80 years), bone diseases, e.g., bone cancers, congenital disabilities, birth defects, revision needs, and accidents. It is essential to select both biologically and mechanically compatible implant materials for such applications. The commonly used implant materials today are austenitic stainless-steel alloys, Co–Cr alloys, Ti, Ta, and their alloys. Recently zirconium (Zr) alloys for biomedical applications are receiving increasing attention due to their two unique properties: 1) the formation of an intrinsic bonelike apatite layer on their surfaces in body environments, and 2) better compatibility with magnetic resonance imaging (MRI) diagnostics due to their intrinsically low magnetic susceptibility, as well as their overall excellent biocompatibility, mechanical properties, and bio-corrosion resistance. In particular, since both of the MRI quality and speed depend on magnetic field strength, there is a compelling drive for the use of high magnetic field strength (>3 Tesla) MRI systems. This requires the availability of implant alloys that can offer much lower susceptibility than the current Ti implant alloys. In that regard, Zr-based alloys offer more promise than Ti-based alloys. This thesis first presents a comprehensive review of the characteristics of commercially pure (CP) Zr and Zr-based alloys as potential orthopaedic and dental implant materials. These include their 1) phase transformations; 2) unique properties including corrosion resistance, biocompatibility, magnetic susceptibility, shape memory effect, and super-elasticity; 3) mechanical properties; 4) current orthopaedic and dental applications, and; 5) the d-electron theory for Zr alloy design and novel Zr-alloys, and 6) future directions for extending the use of Zr-alloys as orthopaedic and dental implants are discussed. Then following a detailed analysis of the design methods for low elastic modulus Ti alloys, the d-electron theory and the ⁄ ratio approach are used together to design nine strong, ductile, and low elastic modulus Ti-Nb-Zr alloys. Among them, five are Zr-based Ti-Nb-Zr alloys, and four are Tibased Ti-Nb-Zr alloys. To assess Ti-Nb-Zr alloys, it is important to understand the influence of Zr on the β-phase stability of Ti-Nb-Zr alloys. The concept of the Mo equivalence (MoEq), proposed by Molchanova (Phase Diagrams of Titanium Alloys, 1965), has been commonly used as a general guideline to gauge the stability of a β-Ti alloy. A critical literature review has shown that all four existing Mo-Eq expressions deviate substantially from experimental observations and the well-established d-electron theory in predicting the β-phase stability of Ti-Nb-Zr alloys. The reasons are that existing Mo-Eq expressions either completely neglect or significantly overestimate the β-stabilizing effect of Zr. In this thesis, a new Mo-Eq expression, i.e., (Mo-Eq) Ti-Nb-Zr = 0.238Nb (wt.%) + 0.11Zr (wt.%) + 0.97, has been defined for Ti-Nb-Zr alloys in order to properly address the β-stabilizing effect of Zr. This new Mo-Eq expression shows good consistency with both experimental observations and the d-electron theory in predicting the β-phase stability of various Ti-Nb-Zr alloys. With necessary modifications, the approach developed is expected to be also applicable to the assessment of the β-phase stability in other Zr-containing Ti alloys. Three different methods: tension, compression, and ultrasonic tests, are used to determine the elastic modulus of the five Zr-Ti-Nb alloys (Zr-45Ti-15Nb, Zr-33Ti-15Nb, Zr-28Ti-15Nb, Zr-35Ti-10Nb, and Zr-30Ti-20Nb, in at.%) alloys. The as-cast tensile, compressive and ultrasonic elastic moduli of these alloys range from 58-79GPa, 45-57GPa and 60-95GPa respectively. The two Zr-Ti-Nb alloys (Zr-based Ti-6Nb-53Zr and Ti-18Nb-51Zr) from the literature, which reportedly have the lowest elastic moduli, are prepared and tested for comparison as a point of reference. The dependence of elastic moduli on the test methods, phase constitutes as well as and ⁄ ratio is systematically investigated. The reassessed Mo-Eq. values change linearly with the ⁄ ratio for the above seven alloys. The current work also indicates that a small amount of the ω-phase along with β and α″-phases, and the condition of ⁄ ≈ 4.15, can lead to low elastic modulus for Zr-Ti-Nb alloys. Therefore, a modified relationship between the phases and the elastic modulus has been suggested, which is: Eα″ < 40 GPa < Eβ ≈ 60-90 GPa < Eα ≈ 100 GPa < Eω ≈ 130-220 GPa. This study identifies that as-cast Zr-28Ti-15Nb and Zr-33Ti-15Nb alloys can offer low elastic modulus (~60 GPa, tensile and ultrasonic), excellent tensile ductility (~16%), uniform plastic strain (greater than 10%) and sufficiently high tensile yield strength (~650 MPa) for implant applications. While designing the Zr-Ti-Nb alloys, this thesis author realized that Ti-Nb-Zr alloys could also offer low elastic modulus. As a result, four new Ti-Nb-Zr alloys (Ti-26Zr-10Nb, Ti25Zr-15Nb, Ti-22Zr-15Nb, and Ti-21Zr-20Nb) are designed by the d-electron theory and ⁄ ratio. The as-cast tensile, compressive and ultrasonic elastic moduli of these alloys are in the range of 58-71GPa, 34-60GPa and 52-83GPa respectively. The effects of alloying elements on microstructures, mechanical properties i.e. tensile strength, yield strength, compressive yield strength, elastic modulus, elastic energy, and microhardness of these newly designed alloys have been investigated. Ti-Nb-Zr alloys also show the linear relationship between MoEq values and ⁄ ratio. The results also confirm that a small amount of ω-phase is not clearly detrimental in reducing the elastic modulus along with β and α″-phase. Therefore, the results from Ti-Nb-Zr alloys strongly agree with the above proposed relationship sequence between the phases and the elastic modulus for Zr-Ti-Nb alloys
Biomimetic porous titanium scaffolds for orthopaedic and dental applications
The development of artificial organs and implants for replacement of injured and diseased hard tissues such as bones, teeth and joints is highly desired in orthopedic surgery. Orthopedic prostheses have shown an enormous success in restoring the function and offering high quality of life to millions of individuals each year. Therefore, it is pertinent for an engineer to set out new approaches to restore the normal function of impaired hard tissues.Over the last few decades, a large number of metals and applied materials have been developed with significant improvement in various properties in a wide range of medical applications. However, the traditional metallic bone implants are dense and often suffer from the problems of adverse reaction, biomechanical mismatch and lack of adequate space for new bone tissue to grow into the implant. Scientific advancements have been made to fabricate porous scaffolds that mimic the architecture and mechanical properties of natural bone. The porous structure provides necessary framework for the bone cells to grow into the pores and integrate with host tissue, known as osteointegration. The appropriate mechanical properties, in particular, the low elastic modulus mimicking that of bone may minimize or eliminate the stress-shielding problem. Another important approach is to develop biocompatible and corrosion resistant metallic materials to diminish or avoid adverse body reaction. Although numerous types of materials can be involved in this fast developing field, some of them are more widely used in medical applications. Amongst them, titanium and some of its alloys provide many advantages such as excellent biocompatibility, high strength-to-weight ratio, lower elastic modulus, and superior corrosion resistance, required for dental and orthopedic implants. Alloying elements, i.e. Zr, Nb, Ta, Sn, Mo and Si, would lead to superior improvement in properties of titanium for biomedical applications.New processes have recently been developed to synthesize biomimetic porous titanium scaffolds for bone replacement through powder metallurgy. In particular, the space holder sintering method is capable of adjusting the pore shape, the porosity, and the pore size distribution, notably within the range of 200 to 500 m as required for osteoconductive applications. The present chapter provides a review on the characteristics of porous metal scaffolds used as bone replacement as well as fabrication processes of porous titanium (Ti) scaffolds through a space holder sintering method. Finally, surface modification of the resultant porous Ti scaffolds through a biomimetic chemical technique is reviewed, in order to ensure that the surfaces of the scaffolds fulfill the requirements for biomedical applications
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
Multidisciplinary investigations on the use of TiNb alloy orthopedic device equipped with low profile antenna as smart sensor
In this paper, a new complex medical device is proposed using TiNb based metallic alloy, acting also as a ground plane for a low profile printed antenna sited on a Polydimethylsiloxane (PDMS) substrate. The first step of the research is oriented on the experimental study of the properties of TiNb based alloy and on the development of the orthopedic device. The second step is focalized on the electromagnetic characterization of the implanted printed antennas. The resulting smart orthopedic device incorporating the antenna and when embedded in a body environment is numerically analyzed from communication point of view. In particular, the radiation characteristics, necessary for the calculation of the link budget when the device is used for communication with the external to the body receiver is considered. Such scenario finds its applications in monitoring some vital human functions for example in post chirurgical rehabilitation or other long-term surveys
Alloy Design and Property Evaluation of Ti-Mo-Nb-Sn Alloy for Biomedical Applications
Ti-Mo alloy containing Nb and Sn were arc melted and composition analyzed by EDX. The XRD analysis indicates that the crystal structure and mechanical properties are sensitive to Sn concentration. A combination of Sn and Nb elements in synergy hindered formation athermal w phase and significantly enhanced b phase stability. The low elastic modulus and good ductility as observed implied that this alloy can be more suitable for biomedical application than the conventional metallic biomaterials from better mechanical compatibility perspective
Titanium-Based alloys and composites for orthopedic implants Applications: A comprehensive review
Abstract
The increasing demand for orthopedic implants has driven the search for materials that combine strength, biocompatibility, and long lifetime. Compared to stainless steel and Co-Cr-based alloys, titanium (Ti) and its alloys are favored for biomedical implants because of their high strength, corrosion resistance, and biocompatibility. This comprehensive review delivers a wide overview of the field of Ti-based biomaterials for orthopedic implants applications, focusing on their types, mechanical and chemical resistance, surface modifications, innovations in fabrication techniques, Ti matrix composites, and machine learning (ML) advancements. Ti alloys of different crystalline phases, including α, near-α, (α + β), β, and shape memory alloys, offer diverse options for orthopedic applications. Strengthening properties, wear, fatigue, and corrosion resistance are crucial factors influencing the performance and reliability of Ti implants. Moreover, this review discussed the challenges to Ti-based biomaterial durability through surface modifications to enhance their biofunction, wear resistance, corrosion resistance, and antibacterial properties. Recent developments in fabrication techniques for Ti-based biomaterials are also discussed. Eventually, this review investigated how ML revolutionized Ti orthopedic implants by providing insights into the behavior of new alloys, aiding in manufacturing optimization, allowing for real-time quality control, and advancing the development of personalized, biocompatible, and reliable implants.Abstract
The increasing demand for orthopedic implants has driven the search for materials that combine strength, biocompatibility, and long lifetime. Compared to stainless steel and Co-Cr-based alloys, titanium (Ti) and its alloys are favored for biomedical implants because of their high strength, corrosion resistance, and biocompatibility. This comprehensive review delivers a wide overview of the field of Ti-based biomaterials for orthopedic implants applications, focusing on their types, mechanical and chemical resistance, surface modifications, innovations in fabrication techniques, Ti matrix composites, and machine learning (ML) advancements. Ti alloys of different crystalline phases, including α, near-α, (α + β), β, and shape memory alloys, offer diverse options for orthopedic applications. Strengthening properties, wear, fatigue, and corrosion resistance are crucial factors influencing the performance and reliability of Ti implants. Moreover, this review discussed the challenges to Ti-based biomaterial durability through surface modifications to enhance their biofunction, wear resistance, corrosion resistance, and antibacterial properties. Recent developments in fabrication techniques for Ti-based biomaterials are also discussed. Eventually, this review investigated how ML revolutionized Ti orthopedic implants by providing insights into the behavior of new alloys, aiding in manufacturing optimization, allowing for real-time quality control, and advancing the development of personalized, biocompatible, and reliable implants
Up-to-Date Knowledge and Outlooks for the Use of Metallic Biomaterials: Review Paper
In all cases, when a material has to be used in medical applications, the knowledge of its physical, chemical and biological properties is of fundamental significance, since the direct contact between the biological system and the considered device could generate reactions whose long-term effects must be clearly quantified. The class of materials that exhibits characteristics that allow their use for the considered applications are commonly called biomaterials. Patients suffering from different diseases generate a great demand for real therapies, where the use of biomaterials are mandatory. Commonly, metallic biomaterials are used because their structural functions; the high strength and resistance to fracture they can offer, provide reliable performance primarily in the fields of orthopedics and dentistry. In metals, because of their particular structure, plastic deformation takes place easier, inducing good formability in manufacturing. The present paper is not encyclopaedic, but reports in the first part some current literature data and perspectives about the possibility of use different class of metallic materials for medical applications, while the second part recalls some results of the current research in this field carried out by the authors
Processing of Ti50Nb50-xHAx composites by rapid microwave sintering technique for biomedical applications
The main objective of this research is to fabricate porous mechanical-tuned (low elastic modulus and high strength) Ti-based composites with improved bioactivity for orthopaedic applications. Another objective is to demonstrate the potential of microwave sintering and temporary space alloying technique to synthesize porous Ti-based composites. In this study, porous Ti50Nb50−xHAx (x = 0, 10 and 20) composite was fabricated for orthopaedic applications using a powder metallurgical and rapid microwave sintering (PM-RMS) process. Effects of key PM-RMS parameters on the structural porosity, compressive strength, and elastic modulus of built composite were then analysed. The microstructure, pore characteristics, and mechanical properties were investigated in detail. Using high hydroxyapatite (HA) content (20%), short sintering time (5 min), and high compacting pressure (200 MPa) appears to be the best condition among those studied in terms of yielding a high degree of structural porosity (21%) and low elastic modulus (25 GPa) in the sintered composite. Since size of pores in the synthesized composite is in the range of 20–30 μm, structural porosity not only reduces elastic modulus but also enhances bio-activity of sintered composite. The combination of highly porous structure, low elastic modulus, high compressive strength, improved corrosion resistance, and enhanced bioactivity makes porous Ti-Nb-HA composites fabricated by microwave sintering process potential and promising candidates for orthopedic applications
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