2,626 research outputs found
Integrated Methodologies and Technologies for the Design of Advanced Biomedical Devices
Biomedical devices with tailored properties were designed using advanced methodologies and technologies. In particular, design for additive manufacturing, reverse engineering, material selection, experimental and theoretical analyses were properly integrated.
The focus was on the design of: i) 3D additively manufactured hybrid structures for cranioplasty; ii) technical solutions and customized prosthetic devices with tailored properties for skull base reconstruction after endoscopic endonasal surgery; iii) solid-lattice hybrid structures with optimized properties for biomedical applications.
The feasibility of the proposed technical solutions was also assessed through virtual and physical models
Numerical thermal study in bone tumor lesion
With the evolution of science and new diagnostic technologies, it was possible to observe a continuous improvement in the treatments in general and in the aid of the patients' quality of life. Malignant tumors can be primary or secondary (metastases), with abnormal growth of cells able to invade other types of tissues and organs through systemic dissemination. Sarcomas are rare primary malignancies formed from mesenchymal tissue and often located at the extremities. In this work, the main objective is to evaluate the minimization of the evolution of bone tumor lesion through the injection of bone cement, filling in the space of the lytic tumor lesion. This methodology allows to verify at the adjacent cement – bone tissue interface, an increase in temperature that can control the local growth of bone metastasis. Different computational models, obtained by medical image processing, will be carried out for two analyses (patient younger than 70 years and older than 70 years). The computational model allows a transient thermal analysis using the finite element method. The temperature results may determine the thermal necrosis effect in the bone tumor lesion. Results will be compared using three different bone cements.info:eu-repo/semantics/publishedVersio
Microstructural characterization and modeling of concrete damaged by Alkali-Silica Reaction (ASR)
La réaction alcalis-silice (RAS) est un des principaux mécanismes nuisibles affectant la durabilité du béton. Le programme de recherche effectué dans le cadre de ce doctorat comprend deux parties (3 phases), soit la caractérisation microstructurale de produits de la RAS et la modélisation du mécanisme d’endommagement du béton par la RAS. Les résultats expérimentaux de cette recherche fourniront de nouvelles données sur les propriétés microstructurales de bétons affectés par la RAS. Les travaux effectués lors de la première phase du programme expérimental avaient pour objectif de caractériser les propriétés micromécaniques des produits de la RAS à l’aide de nouvelles techniques de nano- et micro-indentation, avec emphase portée sur leur propriété en viscosité. Les échantillons de béton utilisés lors du programme d’essais ont été extraits d’un pavage en béton fortement affecté par la RAS et situé dans la région de Bécancour (Québec). Le béton est caractérisé par de nombreuses particules de granulats de calcaire à grains fins contenant des microfissures remplies de produits secondaires de RAS; les fissures s’étendent dans la pâte de ciment pour former un réseau se propageant de particule en particule. Après une préparation soigneuse de l’échantillon par polissage, la surface des particules de granulats et des veinules apparaissant dans ces particules (i.e. microfissures remplies de produits cristallins de réaction) ont été examinées par Atomic Force Microscopy (AFM) avant de procéder aux essais de nano-indentation. Des valeurs de module et de dureté ont été mesurées pour les produits de réaction par micro- et nano-indentation. Les résultats de ces essais indiquent que les produits cristallins de RAS offrent un comportement de relaxation important atteignant environ 40%. De plus, un modèle rhéologique simplifié est proposé permettant de reproduire les courbes de relaxation sous charge et les valeurs asymptotiques. Ces résultats suggèrent que la relaxation des produits de RAS est importante et principalement irréversible. Les travaux de la deuxième phase du programme expérimental ont permis d’explorer l’utilisation d’une nouvelle technique de microscratch afin de caractériser l’énergie de fracturation (i.e. rigidité) des particules de granulats réactifs de type calcaire dans un béton fortement affecté par la RAS (viaduc routier de la région de Québec). Les particules de granulats montraient typiquement un zonage (zones gris-foncées et gris-pâles) entourant des veinules blanchâtres au sein des particules réactives. En tant que référence, un échantillon de calcaire vierge provenant d’une carrière de la région de Québec a été sélectionné et soumis aux mêmes procédures d’essais. En plus des propriétés élastiques, la rigidité des particules de granulats réactives ont été mesurées statistiquement et se situe autour de 1.5 MPam1/2. La rigidité de fracturation des particules de granulats réactives a démontré n’être affecté ni par la direction d’essai par rapport au plan de litage, ni par la zonation qui a d’abord été interprétée comme des portions montrant des signes de réaction. Ainsi, l’endommagement des particules de granulats semble se situer presqu’essentiellement au niveau des microfissures générées dans les particules réactives. La dernière phase du programme expérimental s’est concentrée sur la caractérisation des propriétés en fluage et en relaxation des produits cristallins de RAS remplissant les microfissures des granulats calcaire réactifs (échantillons provenant du pavage fortement affecté par la RAS utilisés lors de la première phase du programme expérimental). Les essais de micro-indentation ont été réalisés sous deux conditions d’humidité relative. Il a été observé qu’une augmentation en humidité relative réduisait fortement la déformation de fluage irréversible des produits cristallins de RAS, qui montrent un temps caractéristique plus grand. Ainsi, la teneur en eau semble favoriser le mécanisme de glissement irréversible le long ou entre les plaquettes des produits cristallins (rosettes lamellaires) de RAS sous charge constante. Finalement, les implications des résultats de ces travaux sont discutées en lien avec le processus de génération de pression à l’intérieur des particules de granulats réactives. Les propriétés rhéologiques des produits de RAS peuvent jouer un rôle critique lors du relâchement des contraintes internes induites par l’expansion de ces produits. Enfin, un modèle simplifié « 1D » est proposé comme nouvel outil de recherche, et ce afin de prendre en compte les principaux résultats de cette étude, i.e. les propriétés visco-élastiques des produits de RAS et les propriétés de rigidité des particules de granulats réactives.The Alkali-Silica Reaction (ASR) is one main detrimental factor to affect the durability of concrete. The research comprises two parts, i.e. microstructural characterization of ASR products (3 phases), and modeling of concrete damage due to ASR. The experimental results will provide new findings on the microstructure properties of ASR-damaged concrete. The work in the first phase of the research aims at characterizing the micromechanical properties of ASR products by new techniques of nanoindentation and micro-indentation, with emphasis on their viscous behavior. The concrete samples were extracted from a heavily ASR-affected concrete pavement in Bécancour (Québec). The concrete is characterized by numerous fine-grained limestone aggregate particles with microcracks filled with secondary reaction products that extend into the cement into a network from one aggregate particle to another. After careful sample preparation (polishing), the surface of the aggregate particle and of the veinlets (i.e. cracks filled with crystalline ASR product within the aggregate particles) was examined by Atomic Force Microscopy (AFM) before nanoindentation testing. Both nanoscale and microscale indentation modulus and hardness of ASR products were measured. The test results show that ASR crystalline products exhibit important relaxation behavior of about 40%. Then, a simplified rheological model was proposed to fit the load relaxation curves and their asymptotic values. These results suggest that ASR product relaxation is significant and mostly irreversible. The second research phase explored the use of the novel micro-scratch technique to characterize the fracture energy (i.e., toughness) of the ASR-affected limestone aggregate particles within a core specimen extracted from a heavily ASR-affected concrete bridge from the Québec City area. The ASR-affected aggregate particles were typically showing “zoning” (i.e. light grey and dark grey) surrounding white veinlets within reacted limestone aggregate particles. As a reference, an undamaged/virgin quarried limestone specimen from a local quarry was selected and subjected to similar testing. Besides the elastic properties, the toughness of the reactive aggregate particles was statistically measured to be around 1.5 MPam1/2. The fracture toughness of reactive aggregate particles was affected neither by the bedding line directions nor by the “zoning” that was first thought to correspond to “reacted” portions of the particles. Besides the major cracks filled by ASR products, the results indicated that the surrounding reactive aggregate was not characterized by any significant internal damage distribution. In the later phase of the experimental program, our research focused on characterizing the creep and stress relaxation properties of the ASR crystalline products typically filling microcracks within reactive limestone particles (specimen from the heavily ASR-affected concrete pavements in Bécancour (Québec) used in phase 1). The testing carried out was micro-indentation under controlled relative humidity. It was found that an increase in relative humidity strongly reduces the irreversible creep deformation of ASR crystalline products, which act a greater characteristic time. That is, the water content seems to favor irreversible sliding mechanisms along/between the ASR crystals under constant load. Finally, the implications the research findings are discussed with respect to the stress build-up process within reactive aggregate particles. The rheological property of ASR products may play a critical role to releasing the internal stress induced by the ASR product expansion. Finally, a “1D thought model” is proposed as a new research avenue to account for the major results of this work into ASR-damaged concrete modeling, i.e., the visco-elastic property of ASR products and the damage toughness of reactive aggregates
Multiscale poroelastic modeling of bone
Total Hip Arthroplasty is nowadays one of the most performed orthopedic surgery and is
representing a major health and economic issue. Bone is a complex material showing a
hierarchical and porous structure, but also a natural ability to remodel itself thanks to
specific cells, which are sensitive to fluid flows. Based on these characteristics, a
multiscale numerical model has been developed within this thesis in order to simulate the
bone response under external mechanical solicitations. The developed model relies on the
homogenization technique for periodic structures based on an asymptotic expansion. It
simulates cortical bone as a homogeneous structure. The first application of the
developed model is the case of the loading of a finite volume of bone, allowing for the
determination of an equivalent poroelastic stiffness. Focusing on two extreme fluid
boundary conditions (impermeable walls and atmospheric pressure), the analysis of the
corresponding structural response provides an overview of the fluid contribution to the
poroelastic behavior, impacting the stiffness of the considered material. To validate the
developed model, both a numerical and an experimental validation are realized. The
numerical validation consists in the variation of parameters such as material properties or
boundary conditions to estimate the accuracy of the model tendencies. Regarding the
experimental validation, a cubic trabecular bone sample, extracted from a human hip and
put under a compressive load, has been used. Increasing the load applied on the top of
the bone specimen, the displacement is extracted, allowing to computation of the
equivalent strain-stress curve. The equivalent stiffness of the bone specimen calculated
numerically is then compared with the one from the experiments. A good agreement
between the curves attests the validity of the developed numerical model, accounting for
both the solid matrix and fluid contributions
Synthesis and characterization of calcium phosphate cement based macroporous scaffolds
Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2012Includes bibliographical references (leaves: 254-267)Text in English; Abstract: Turkish and Englishxviii, 315 leavesThe goal of this thesis is to synthesize unique, clinically relevant macroporous calcium phosphate cement blocks to be utilized both in vivo and in vitro tissue engineering applications. Calcium phosphate cements which essentially consist of hydroxyapatite or brushite are constantly improved to overcome their inherent shortcomings such as low strength, low functional porosity, and low resorption. Recent literature on the topic points to monetite forming cements as an alternative phase. A novel method to utilize monetite that is finer and stronger with respect to brushite in load bearing scaffold applications is introduced in the results section of this thesis as a contribution to ever growing literature on this scope. In the preliminary study on the conversion extent of apatite forming cement, ionic strength of the setting liquid was determined as the prime effective factor on monetite conversion extent. Subsequently brushite forming β-tricalcium phosphate – monocalcium phosphate monohydrate cement system was modified by NaCl and citric acid so that brushite formation was selectively inhibited. Singular and synergistic monetite promoting effects of NaCl and citric acid were determined by monitoring the kinetics of cement setting in excess setting liquid. Spectrometric studies revealed the difference in brushite and monetite crystal surface site density which enabled selective inhibition of brushite and promotion of monetite by the synergistic effect of NaCl anc citric acid. Proposed phase control mechanism enables tailoring the composition of biphasic cements comprising of a predetermined monetite content and brushite or hydroxyapatite. In the final stage of the thesis, size distributed NaCl particles were introduced into the cement paste containing optimum amount of citric acid to enable complete monetite formation. Resultant macroporous monetite blocks were characterized in terms of microporosity, macroporosity, density, morphology, strength, phase composition, and surface area. Interconnectivity of the cement was optimized based on the correlation of porogen size distribution and morphological data
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
Cements of doped calcium phosphates for bone implantation
Doutoramento em CiĂŞncia e Engenharia de MateriaisO principal objectivo deste estudo foi o desenvolvimento de cimentos Ă base de fosfatos de cálcio dopados com Mg, Sr e Zn, para aplicações clĂnicas. A sĂntese dos pĂłs foi obtida atravĂ©s de reacções de precipitação, seguido de tratamento tĂ©rmico de forma a obter as fases mais apropriadas, a (alpha) e b (beta)-TCP. A caracterização dos pĂłs envolveu a quantificação de fases e o refinamento estrutural de fases atravĂ©s da análise de difracção de raios-X por refinamento de Rietveld, bem como, análise da área superficial por BET, e respectivos tamanhos de partĂcula. Os cimentos foram preparados atravĂ©s da mistura dos pĂłs com meios lĂquidos diferentes, usando ácido cĂtrico como acelerador de presa, e o polietilenoglicol (PEG) e o hidroxil propilmetilcelulose (HMPC) como agentes gelificantes. A formação da brushite foi um dos produtos resultantes obtidos da hidratação dos cimentos. Do ponto de vista de aplicação clĂnica, os cimentos foram caracterizados em termos de presa, injectabilidade, análise calorimĂ©trica e resistĂŞncia mecânica. Os presentes resultados demonstraram que a incorporação de iões nos cimentos levou a uma melhoria significativa das propriedades destes quando comparados com TCP puro. Os resultados obtidos demonstraram ainda que o tempo inicial de presa tende a decrescer na presença de modificadores reolĂłgicos, uma vez que estes aumentam a viscosidade das pastas, e aumenta com o acrĂ©scimo da razĂŁo L/P, tendo sido considerada a gama de 0.30-0.34 mL g-1 como aceitável para manusear as pastas. As pastas cimentĂcias apresentaram uma boa injectabilidade, nomeadamente o seu comportamento apĂłs extrusĂŁo, com aplicação de uma força máxima de 100 N. Investigou-se ainda, com estes testes, a ausĂŞncia do efeito de “filter-pressing” e que as pastas foram totalmente expelidas para uma razĂŁo L/P de 0.36 mLg-1. Os testes de calorimetria isotĂ©rmica demonstraram que as pastas apresentam reacções exotĂ©rmicas, referentes Ă dissolução dos pĂłs de partida e Ă formação de fases intermĂ©dias; e Ă nucleação e crescimento da brushite. ResistĂŞncias Ă compressĂŁo dos cimentos estudados, apĂłs imersĂŁo numa solução de PBS durante 48h situam-se entre 1-30 MPa, valores reportados para o osso trabecular. Testes de citotoxicidade, bioactividade e biocompatibilidade dos cimentos foram obtidos atravĂ©s de testes de culturas celulares, mostrando a nĂŁotoxicidade destes. A biocompatibilidade in vivo e a reabsorção dos cimentos foram avaliadas em estudos histolĂłgicos e histomorfomĂ©tricos de secções descalcificadas obtidas atravĂ©s de ensaios de experimentação animal, usando o porco como modelo. Os resultados mostraram que os cimentos implantados sĂŁo biocompatĂveis e osteocondutivos, sem evidĂŞncia de reacções infecciosas, e portanto, bons candidatos para aplicação como substitutos Ăłsseos.The main objective of this study was the development of cements based on calcium phosphates doped with Mg, Sr and Zn, for clinical applications. Powder synthesis was obtained through precipitation reactions, followed by heat treatment in order to obtain appropriate phases, a (alpha) and b (beta)-TCP. The cements were prepared through mixing the powders with different liquids, using citric acid as setting accelerator, and polyethyleneglycol and hydroxyl propylmethylcellulose as gelling agents. Brushite was the end product of the hydration reaction. Injectability and setting behaviour were accessed through rheological measurements, extrusion, calorimetric analysis, Vicat and Gilmore needles. Phase quantification and the structural refinement of powders and cements were determined through X-ray diffraction with Rietveld refinement, as well as, BET specific surface area and particle size analysis. Mechanical strengths of wet hardened cements were evaluated. The results obtained showed that the incorporation of ions into cements led to a significant improvement of their overall properties. Initial setting time increased in the presence of rheological modifiers due to their specific roles at the solid/liquid interface and with increasing L/P ratio. Acceptable workability pastes were obtained for L/P ratios in the range of 0.30-0.34 mL g-1. The cement pastes presented good injectability even under a maximum applied force of 100 N. Filter pressing effects were absent, and all cement pastes could be fully injected for LPR > 0.36 mL g-1. Isothermal calorimetry revealed that hydration reactions produce exothermic effects due to: (i) dissolution of the starting powders and formation of intermediate phases; and (ii) nucleation and growth of brushite crystals. The intensity of the exothermic effects depended on doping element, being stronger in the case of Sr. Wet compressive strength of the cement specimens (after immersion in PBS solution for 48 h) was in the range of values reported for trabecular bone (10-30 MPa). Cell cultures used to evaluate citotoxicity, bioactivity and biocompatibility of cements revealed no toxic effects. The biocompatibility in vivo and cements resorption were evaluated using a pig model through histological and histomorphometric studies of decalcified sections. The results show that the implanted cements are biocompatible and osteoconductive, without foreign body reaction. These properties make them good candidates for applications as bone substitutes
Technology transfer: Transportation
Standard Research Institute (SRI) has operated a NASA-sponsored team for four years. The SRI Team is concentrating on solving problems in the public transportation area and on developing methods for decreasing the time gap between the development and the marketing of new technology and for aiding the movement of knowledge across industrial, disciplinary, and regional boundaries. The SRI TAT has developed a methodology that includes adaptive engineering of the aerospace technology and commercialization when a market is indicated. The SRI Team has handled highway problems on a regional rather than a state basis, because many states in similar climatic or geologic regions have similar problems. Program exposure has been increased to encompass almost all of the fifty states
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