Joining Technologies for Cardiovascular Implants

Nitinol (NiTi) is widely used in the medical field, due to its unique superelastic and shape memory properties. Nitinol undergoes thermo-mechanical processing, such as thermosetting, laser-cutting and joining for medical application, however these processes can alter these properties. The Temperature-dependant characteristics of nitinol can work as a disadvantage to fully exploit this alloy for biomedical applications. Three different themes are explored in this thesis, a) the properties of nitinol-nitinol bonds compared to base metal b) understanding how welding method affects bond properties and joint strength and c) investigating the optimum method for bonding nitinol to non-metal such as biopolymers. In order to overcome the above-mentioned limitations, different joining techniques for nitinol was investigated in this study. Initially, the effect of different joining techniques on nitinol properties, in comparison to base metal was investigated. Experimental results mainly focus on the nitinol to nitinol joining techniques, including laser micro welding (Ytterbium-fiber laser and quansi continuous wave laser), capacitor discharge welding, percussive arc welding, adhesive bonding, PEEK shrink tubes and crimping. The effects of these joining techniques on the microstructure, superelastic properties and strength of a joint are analysed and compared. The mechanical tests and analytical results suggest that the use of laser welding should be employed for the development of new and improved medical implants. However, long-term studies are required which are currently underway to further develop this technique. For various medical applications, metal components are mainly used to provide the strength and stiffness whereas polymeric biomaterials can provide unique chemical properties and manufacturing, benefits as they can be moulded and shaped into complex designs depending on the application. However, due to the massive difference in physical and chemical properties of metal and polymers, joining them generates new challenges. Hence, the third part of the thesis explores different approaches to join nitinol to polymeric biomaterials including Polyetheretherketone (PEEK), and polyethylene terephthalate (PET) fabric, commercially known as Dacron®. Due to the difference in chemical and physical properties of nitinol to PET, it was difficult to join them without using an interlayer. Thus, a polyurethane coating was used as an interlayer to bond nitinol to PET fabric. This study also provides an insight into different surface treatments used to improve the bonding between nitinol and polyurethane coating including chemical etching and cold atmospheric plasma treatment. The study shows how an appropriate selection of the joining technique can enhance the exploitation of properties of nitinol alloy in the clinical area, resulting in improvements in the safety and durability of medical devices

Wear behaviour of Ti6Al4V femoral head surfaces functionalized through ultrasonic vibration turning for drug delivery

La tesi presenta una possibile funzionalizzare di teste di protesi femorali in Ti6Al4V per mezzo di una lavorazione meccanica (l'Ultrasonic Vibration Turning UVT). Tale funzionalizzazione è una potenziale soluzione per risolvere l'infiammazione post-operatoria per mezzo del drug delivery, in quanto permette di creare delle microbuche superficiali, possibili siti di immagazzinamento di medicinale

Machining of biocompatible materials: Recent advances

Machining of biocompatible materials is facing the fundamental challenges due to the specific material properties as well as the application requirements. Firstly, this paper presents a review of various materials which the medical industry needs to machine, then comments on the advances in the understanding of their specific cutting mechanisms. Finally it reviews the machining processes that the industry employs for different applications. This highlights the specific functional requirements that need to be considered when machining biocompatible materials and the associated machines and tooling. An analysis of the scientific and engineering challenges and opportunities related to this topic are presented

Surface treatment of titanium with antibacterial properties for biomedical applications

Titanium and its derivative alloys are attracting increasing interest in the medical field due to the many advantages it appears to possess. Indeed, titanium is widely used as a biomaterial for implants and prostheses in the fields of orthodontics and orthopaedics, thanks to its high biocompatibility regarding low ion release. Titanium also has outstanding corrosion resistance, great mechanical properties in terms of high hardness, low modulus of elasticity, low density, and high fatigue limit, which is a requirement for most implants. The above-mentioned remarkable biocompatibility of titanium is related to the development of a native oxide layer on its surface when exposed to air. In addition, this layer can develop in certain arranged patterns, that prove to be useful for the local administration of antibacterial agents, thus offering an alternative to aggressive surgical procedures against implant-related infections. Indeed, the main causes of implant failure are prosthesis-related infections. Thus, the aim of this project is to prevent infection of titanium implants when embedded in the body by loading the titanium oxide layer with an antibacterial agent and to develop coatings to reach release close to the zero kinetic order. For this purpose, a specific titanium dioxide structure, titanium nanotubes, was developed using an electrochemical oxidation reaction, and studied by looking at the different parameters affecting their geometry. The nanotubes were then loaded with an antibacterial agent and coated with two different coatings. These coatings are intended to degrade gradually to allow the antibacterial agent to be released with a steady flow without causing an overdose and thus prevent the growth of bacterial biofilms. Titanium nanotubes samples were characterized using a Scanning Electron Microscope (SEM) allowing to see the influence of the growing parameters. Coatings were characterized using Fourier-Transform Infrared Spectroscopy (FTIR). Various bacteriological studies were carried to see the impact of the different parameters, including surface geometries and types of coatings. The results were analyzed and showed successful growth of nanotubes capable of storing a bactericidal agent. In addition, the coatings were developed with great success. Bacterial studies showed a great antibacterial effect of the coatings or antibacterial loaded nanotube samples. However, the aspect of zero-order diffusion will not have been addressed in this project.El titanio y sus aleaciones derivadas suscitan un interés creciente en el ámbito médico debido a las numerosas ventajas que parece poseer. En efecto, el titanio se utiliza ampliamente como material para implante y prótesis en los campos de la ortodoncia y la ortopedia, gracias a su elevada biocompatibilidad en cuanto a su baja liberación de iones. El titanio también posee una extraordinaria resistencia a la corrosión, grandes propiedades mecánicas en términos de alta dureza, bajo módulo de elasticidad, baja densidad y alto límite de fatiga, lo cual es un requisito para la mayoría de los implantes. La notable biocompatibilidad del titanio antes mencionada está relacionada con el desarrollo de una capa de óxido nativo en su superficie cuando se expone al aire. Además, esta capa puede desarrollarse en determinados patrones dispuestos, que resultan útiles para la administración local de agentes antibacterianos, ofreciendo así una alternativa a los procedimientos quirúrgicos agresivos contra infecciones vinculadas al implante. De hecho, las principales causas de fracaso de los implantes son las infecciones relacionadas con las prótesis. Así pues, el objetivo de este proyecto es prevenir la infección de implante de titanio cuando está implantado en el paciente cargando la capa de óxido de titanio con un agente antibacteriano y desarrollar recubrimientos que alcancen una liberación próxima al orden cinético cero. Para ello, se desarrolló una estructura específica de dióxido de titanio, los nanotubos de titanio, mediante una reacción de oxidación electroquímica, y se estudiaron los distintos parámetros que afectan a su geometría. A continuación, los nanotubos se cargaron con un agente antibacteriano y se recubrieron con dos recubrimientos diferentes. Estos recubrimientos están destinados a degradarse gradualmente para permitir que el agente antibacteriano se libere con un flujo constante sin causar una sobredosis y evitar así el crecimiento de biopelículas bacterianas. Las muestras de nanotubos de titanio se caracterizaron mediante microscopio electrónico de barrido (SEM) que permitió ver la influencia de los parámetros de crecimiento. Los recubrimientos se caracterizaron mediante espectroscopia infrarroja con transformada de Fourier (FTIR). Se llevaron a cabo varios estudios bacteriológicos para ver el impacto de los diferentes parámetros, incluidas las geometrías de superficie y los tipos de recubrimientos. Los resultados se analizaron y mostraron un crecimiento satisfactorio de nanotubos capaces de almacenar un agente bactericida. Además, los recubrimientos se desarrollaron con gran éxito. Los estudios bacteriológicos mostraron un gran efecto antibacteriano de los recubrimientos o de las muestras de nanotubos cargadas con antibacterianos. Sin embargo, en este proyecto no se abordó el estudio de la cinética de la difusión.Le titane et ses alliages dérivés suscitent un intérêt croissant dans le domaine médical en raison des nombreux avantages qu'il semble posséder. En effet, le titane est largement utilisé comme matériaux pour implants et prothèses dans les domaines de l'orthodontie et de l'orthopédie, grâce à sa grande biocompatibilité liée à sa faible libération d'ions. Le titane présente également une résistance exceptionnelle à la corrosion ainsi que des propriétés mécaniques importantes, comme une dureté élevée, un faible module d'élasticité, une faible densité et une limite de fatigue élevée, ces conditions étant des prérequis pour la plupart des implants. La remarquable biocompatibilité du titane susmentionnée est liée au développement d'une couche d'oxyde natif à sa surface lorsqu'il est exposé à l'air. En outre, cette couche peut se développer selon certains schémas arrangés, qui s'avèrent utiles pour l'administration locale d'agents antibactériens, offrant ainsi une alternative aux procédures chirurgicales agressives. En effet, les principales causes d'échec des implants sont les infections liées aux prothèses. Ainsi, l'objectif de ce projet est de prévenir l'infection d’implants en titane lorsqu'ils sont intégrés dans le patient en chargeant la couche d'oxyde de titane d'un agent antibactérien et de développer des revêtements permettant d'atteindre une libération de celui-ci proche de l'ordre cinétique zéro. À cette fin, une structure spécifique de dioxyde de titane, les nanotubes de titane, a été développée à l'aide d'une réaction d'oxydation électrochimique, et étudiée en examinant les différents paramètres affectant leur géométrie. Les nanotubes ont ensuite été chargés d'un agent antibactérien et recouverts de deux revêtements différents. Ces revêtements sont destinés à se dégrader progressivement pour permettre à l'agent antibactérien d'être libéré avec un débit régulier sans provoquer de surdosage et ainsi empêcher la croissance de biofilms bactériens. Les échantillons de nanotubes de titane ont été caractérisés à l'aide d'un microscope électronique à balayage (MEB) permettant de voir l'influence des paramètres de croissance. Les revêtements ont été caractérisés par spectroscopie infrarouge à transformée de Fourier (FTIR). Diverses études bactériologiques ont été réalisées pour voir l'impact des différents paramètres, notamment les géométries de surface et les types de revêtements. Les résultats ont été analysés et ont montré une croissance réussie des nanotubes capables de stocker un agent bactéricide. En outre, les revêtements ont été développés avec un grand succès. Les études bactériennes ont montré un effet antibactérien remarquable des revêtements ainsi que des échantillons de nanotubes chargés d'antibactériens. Cependant, l'étude de la cinétique de diffusion n'aura pas été abordé dans ce projet.Incomin

Ultrasound for Material Characterization and Processing

Ultrasonic waves are nowadays used for multiple purposes including both low-intensity/high frequency and high-intensity/low-frequency ultrasound. Low-intensity ultrasound transmits energy through the medium in order to obtain information about the medium or to convey information through the medium. It is successfully used in non-destructive inspection, ultrasonic dynamic analysis, ultrasonic rheology, ultrasonic spectroscopy of materials, process monitoring, applications in civil engineering, aerospace and geological materials and structures, and in the characterization of biological media. Nowadays, it is an essential tool for assessing metals, plastics, aerospace composites, wood, concrete, and cement. High-intensity ultrasound deliberately affects the propagation medium through the high local temperatures and pressures generated. It is used in industrial processes such as welding, cleaning, emulsification, atomization, etc.; chemical reactions and reactor induced by ultrasonic waves; synthesis of organic and inorganic materials; microstructural effects; heat generation; accelerated material characterization by ultrasonic fatigue testing; food processing; and environmental protection. This book collects eleven papers, one review, and ten research papers with the aim to present recent advances in ultrasonic wave propagation applied for the characterization or the processing of materials. Both fundamental science and applications of ultrasound in the field of material characterization and material processing have been gathered

Vibrations of high-speed dental handpieces measured using laser vibrometry

Objective: To measure in vitro vibration displacement amplitudes of high-speed dental handpieces under unloaded and loaded conditions using a non-contact Scanning Laser Vibrometer (SLV). Methods: Five turbines (two KaVo, three W&H) and two speed-increasing handpieces (one KaVo and one W&H) were investigated using a Polytec SLV (PSV-300). Handpieces were operated under various conditions which included equipping with no rotary cutting instrument (RCI), with a diamond RCI, or with a tungsten carbide bur. Repeated measurements were taken from six selected points on the handpiece. Further tests were performed to study the influence of increasing loads (50 to 200 g) whilst cutting into extracted human teeth. Results were investigated using analysis of variance (ANOVA) at a significance level of p = 0.05, and post hoc tests. Results: Maximum handpiece vibrations were less than 4 μm. Significant differences were found between some handpiece models when unloaded. Increasing the load from 100 to 150 g corresponded with an increase in vibration amplitudes. Interactions between RCI type and handpiece model significantly affected vibrations. Conclusions: Variations in displacement amplitudes were observed under different conditions. It was difficult to determine consistent patterns of vibration. Further research is needed in this area

Thick film PZT transducer arrays for particle manipulation

This paper reports the fabrication and evaluation of a two-dimensional thick film PZT ultrasonic transducer array operating at about 7.5 MHz for particle manipulation. All layers on the array are screen-printed and sintered on an Al2O3 substrate without further processes or patterning. The measured dielectric constant of the PZT is 2250 ± 100, and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis has been used to predict the behaviour of the array and impedance spectroscopy and laser vibrometry have been used to characterise its performance. The measured deflection of a single activate element is on the order of tens of nanometres with 20 Vpp input. Particle manipulation experiments have been performed by coupling the thick film array to a capillary containing polystyrene microspheres in water

Investigating the motility of Dictyostelium discodeum using high frequency ultrasound as a method of manipulation

Cell motility is an essential process in the development of all organisms. The earliest stages of embryonic development involve massive reconfigurations of groups of cells to form the early body structures. Embryos are very complex systems, and therefore to investigate the molecular and cellular basis of development a simpler genetically tractable model system is used. The social amoeba Dictyostelium Discoideum is known to chemotax up a chemical gradient. From previous work, it is clear that cells generate forces in the nN range. This is above the limit of optical tweezers and therefore we are investigating the use of acoustic tweezers instead. In this paper, we present recent progress of the investigation in to the use of acoustic tweezers for the characterisation of cell motility and forces. We will describe the design, modelling and fabrication of several devices. All devices use high frequency (>15MHz) ultrasound to exert a force on the cells to position and/or stall them. Also, each device is designed to be suitable for the life-sciences laboratory where form-factor and sterility is concerned. A transducer (LiNo) operating at 24 MHz excites resonant acoustic modes in a rectangular glass capillary (100um by 2mm). This device is used to alter the directionality of the motile cells inside the fluid filled capillary. A quarter-ring PZT26 transducer operating at 20.5MHz is shown to be useful for manipulating cells using axial acoustic radiation forces. This device is used to exert a force on cells and shown to pull them away from a coverslip. The presented devices show promise for the manipulation of cells in suspension. Currently the forces produced are below that required for adherent cells; the reasons for this are discussed. We also report on other issues that arise when using acoustic waves for manipulating biological samples such as streaming and heating

Remanufacturing and Advanced Machining Processes for New Materials and Components

"Remanufacturing and Advanced Machining Processes for Materials and Components presents current and emerging techniques for machining of new materials and restoration of components, as well as surface engineering methods aimed at prolonging the life of industrial systems. It examines contemporary machining processes for new materials, methods of protection and restoration of components, and smart machining processes. • Details a variety of advanced machining processes, new materials joining techniques, and methods to increase machining accuracy • Presents innovative methods for protection and restoration of components primarily from the perspective of remanufacturing and protective surface engineering • Discusses smart machining processes, including computer-integrated manufacturing and rapid prototyping, and smart materials • Provides a comprehensive summary of state-of-the-art in every section and a description of manufacturing methods • Describes the applications in recovery and enhancing purposes and identifies contemporary trends in industrial practice, emphasizing resource savings and performance prolongation for components and engineering systems The book is aimed at a range of readers, including graduate-level students, researchers, and engineers in mechanical, materials, and manufacturing engineering, especially those focused on resource savings, renovation, and failure prevention of components in engineering systems.

Investigation into vibration assisted micro milling: theory, modelling and applications

PhD ThesisPrecision micro components are increasingly in demand for various engineering industries, such as biomedical engineering, MEMS, electro-optics, aerospace and communications. The proposed requirements of these components are not only in high accuracy, but also in good surface performance, such as drag reduction, wear resistance and noise reduction, which has become one of the main bottlenecks in the development of these industries. However, processing these difficult-to-machine materials efficiently and economically is always a challenging task, which stimulates the development and subsequent application of vibration assisted machining (VAM) over the past few decades. Vibration assisted machining employs additional external energy sources to generate high frequency vibration in the conventional machining process, changing the machining (cutting) mechanism, thus reducing cutting force and cutting heat and improving machining quality. The current awareness on VAM technology is incomplete and effective implementation of the VAM process depends on a wide range of technical issues, including vibration device design and setup, process parameters optimization and performance evaluation. In this research, a 2D non-resonant vibration assisted system is developed and evaluated. Cutting mechanism and relevant applications, such as functional surface generation and microfluidic chips manufacturing is studies through both experimental and finite element analysis (FEA) method. A new two-dimensional piezoelectric actuator driven vibration stage is proposed and prototyped. A double parallel four-bar linkage structure with double layer flexible hinges is designed to guide the motion and reduce the displacement coupling effect between the two directions. The compliance modelling and dynamic analysis are carried out based on the matrix method and lagrangian principle, and the results are verified by finite element analysis. A closed loop control system is developed and proposed based on LabVIEW program consisting of data acquisition (DAQ) devices and capacitive sensors. Machining experiments have been carried out to evaluate the performance of the vibration stage and the results show a good agreement with the tool tip trajectory simulation results, which demonstrates the feasibility and effectiveness of the vibration stage for vibration assisted micro milling. The textured surface generation mechanism is investigated through both modelling and experimental methods. A surface generation model based on homogenous matrices transformation is proposed by considering micro cutter geometry and kinematics of vibration assisted milling. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted micro milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. A new contact model, which considers both liquid infiltration effects and air trapped in the microstructure, is proposed for predicting the wettability of the fish scales surface texture. The following surface textures are used for T-shaped and Y-shaped microchannels manufacturing to achieve liquid one-way flow and micro mixer applications, respectively. The liquid flow experiments have been carried out and the results indicate that liquid flow can be controlled effectively in the proposed microchannels at proper inlet flow rates. Burr formation and tool wear suppression mechanisms are studied by using both finite element simulation and experiment methods. A finite element model of vibration assisted micro milling using ABAQUS is developed based on the Johnson-Cook material and damage models. The tool-workpiece separation conditions are studied by considering the tool tip trajectories. The machining experiments are carried out on Ti-6Al-4V with coated micro milling tool (fine-grain tungsten carbides substrate with ZrO2-BaCrO4 (ZB) coating) under different vibration frequencies (high, medium and low) and cutting states (tool-workpiece separation or nonseparation). The results show that tool wear can be reduced effectively in vibration assisted micro milling due to different wear suppression mechanisms. The relationship between tool wear and cutting performance is studied, and the results indicate that besides tool wear reduction, better surface finish, lower burrs and smaller chips can also be obtained as vibration assistance is added