Wear of PEEK-Ti6Al4V systems under micro-abrasion and linear sliding conditions

Dissertação de mestrado integrado em Engenharia Biomédica

Controlled aggregation of gold nanoparticles in a di-ureasilmatrix. Optical and micro indentation investigation

Nanocomposite materials with an organic-inorganic urea-silicate (di-ureasil) based matrix containing gold nanoparticles (NPs) were synthesized and characterized by optical (UV/Vis) spectroscopy and indentation measurement. The urea silicate gels were obtained by reaction between silicon alkoxyde modified by isocyanate group and polyethylene glycol oligomer with amine terminal groups in presence of catalyst. The latter ensures the successful incorporation of citrate-stabilized gold NPs in the matrix. It is shown that using a convenient destabilizing agent (AgNO3) and governing the preparative conditions, the aggregation degree of gold NPs can be controlled. The developed synthesis procedure significantly simplifies the preparative procedure of gold/urea silicate nanocomposites, compared to the procedure using gold NPs, preliminary covered with silica shells. Mechanical properties of the prepared sample were characterised using depth sensing indentation methods (DSI) and an idea about the type of aggregation structures was suggested.

Silk fibroin based multifunctional materials

Silk fibroin is a commonly available natural biopolymer produced in specialized glands of arthropods, such as silkworms or spiders, scorpions, mites, bees and flies. This biopolymer has a long history of use in textile production and also as sutures or treatment of skin wounds. Silk fibroin has been increasingly explored in other areas of biomedical science where we can find a higher morphological diversification of silk biomaterials like films, electrospun fibers, 3D porous scaffolds or nanoparticles. In recent years it has been demonstrated that fibroin is an excellent material for active components in optical devices. This new application opens the way towards the development of multifunctional optoelectronic devices, which in perspective can be made fully biocompatible and eventually bioresorbable. Moreover, fibroin can be added to other biocomponents in order to modify the biomaterial properties leading to optimized and total different functions. These improvements can go from higher cell adhesion in tissue engineering or enhanced optical transparency, smoothness or flexibility in optoelectronic devices. The tuning and completely understanding of silk fibers physicochemical properties and interaction with other elements are of crucial importance for the improvement of already existent silk-based materials and the basis for the development of new products.

Micro/nano-structured superhydrophobic surfaces in the biomedical field: part I: basic concepts and biomimetic approaches.

Inspired by natural structures, great attention has been devoted to the study and development of surfaces with extreme wettable properties. The meticulous study of natural systems revealed that the micro/nano-topography of the surface is critical to obtaining unique wettability features, including superhydrophobicity. However, the surface chemistry also has an important role in such surface characteristics. As the interaction of biomaterials with the biological milieu occurs at the surface of the materials, it is expected that synthetic substrates with extreme and controllable wettability ranging from superhydrophilic to superhydrophobic regimes could bring about the possibility of new investigations of cellâ material interactions on nonconventional surfaces and the development of alternative devices with biomedical utility. This first part of the review will describe in detail how proteins and cells interact with micro/nano-structured surfaces exhibiting extreme wettabilities.

Síntesis y Caracterización de Materiales Nanoestructurados para el Almacenamiento de Hidrógeno. Hidrogen storage: Synthesis and characterization of nanostructured materials.

El hidrógeno tiene, actualmente, una atención considerable por su posible uso como combustible limpio y otros usos industriales y se ha demostrado que es posible hacer funcionar motores de combustión interna, por lo tanto es una alternativa viable respecto de fuentes de energía no renovables como el petróleo y tal vez sea en el futuro la tecnología más prometedora para reducir la contaminación, conservando el suministro de combustibles fósiles. Uno de los principales problemas para la utilización del hidrógeno como combustible es el del almacenamiento para que pueda ser seguro y transportable con todos los riesgos que esto supone. En este sentido el estudio de la adsorción de polímeros conductores (tal como polianilina, PANI o polipirrol PPy) y su posterior polimerización sobre hospedajes como aluminosilicatos meso y microporosos y carbones mesoporosos, es de suma importancia por sus propiedades para el almacenamiento de H2. El objetivo general de este proyecto es Investigar el almacenamiento de hidrógeno en nuevos composites nano/microestructurados. La síntesis de materiales micro/mesoporosos (MFI, MEL, BEA, L, MS41, SBA-15, SBA-1, SBA-3, SBA-16, CMK-3) para usos como hospedaje se realizan por sol-gel o síntesis hidrotérmica y se modificarán con TiO2, CeO2, ZrO2 y eventualmente con Ir, Ni, Zr. Muestras de estos hospedajes serán expuestos a vapores del monómero puro (anilina o pirrol). Luego se polimerizarán por polimerización oxidativa. Los nanocomposites sintetizados se caracterizarán por XRD, FTIR, DSC, TGA, SEM, TEM, EXFAS, XANES, UV-Vis. La adsorción de hidrógeno sobre los composites se llevará a cabo en un Reactor Parr, desde presiones atmosféricas y a altas presiones y varias temperaturas de adsorción . Los estudios de desorción de hidrogeno se llevarán a cabo en un equipo Chemisorb Micrometrics y se realizarán estudios termogravimétricos y de capacidad de retención de Hidrogeno por el nanocomposite. La importancia del estudio de este proceso tiene importantes implicancias económicas y sociales que serán preponderantes en el futuro debido a las cada vez más exigentes regulaciones ambientales. Además se contribuirá al avance del conocimiento científico, ya que es posible diseñar nuevos materiales, los que además permitirán generar reservorios de H2 con alta eficiencia. Por lo consiguiente: - Se desarrollarán nuevos materiales nanoestructurados, micro y mesoporosos y nanoclusters de especies activas en los hospedajes como así también la inclusión de polímeros (PANI, PPy) dentro de los canales de estos materiales. - Se caracterizarán estos materiales por métodos espectroscópicos (fisicoquímica de superficie). - Se estudiará la adsorción /absorcion de H2 en los nuevos materiales desarrollados. -Se aplicarán métodos de diseño de experimento (RDS), para optimizar el proceso de almacenamiento de H2, nivel de interacción de variables sinérgicas o colinérgicas.

Elaboració de membranes de fibra buida modificades amb nanopartícules metàl·liques per aplicacions catalítiques

Investigación producida a partir de una estancia en la Université Paul Sabatier, Toulouse III - CNRS, entre 2007 y 2009. Durante los últimos años la investigación centrada en nuevos materiales de tamaño nanoscòpico (nanopartículas, quantum dots, nanotubos de carbono,...) ha experimentado un crecimiento considerable debido a las especiales propiedades de los "nanoobjetos" con respecto a magnetismo, catálisis, conductividad eléctrica, etc ... Sin embargo, hoy en día todavía existen pocas aplicaciones de las nanopartículas en temas medioambientales. Uno de los motivos de esta situación es la posible toxicidad de los nanoobjetos, pero existe también una dificultad tecnológica dado que las nanopartículas tienden a agregarse y es muy difícil manipularlas sin que pierdan sus propiedades especiales. Así, aunque la preparación de materiales catalíticos nanoestructurados es muy interesante, es necesario definir nuevas estrategias para prepararlos. Este proyecto de investigación tiene como objetivo principal la preparación de nuevas membranas catalíticas con nanopartículas metálicas en el interior para aplicaciones de tratamiento de agua. La innovación principal de este proyecto consiste en que las nanopartículas no son introducidas en la matriz polimérica una vez preformadas sino que se hacen crecer en el interior de la matriz polimérica mediante una síntesis intermatricial. El único requisito es que la matriz polimérica contenga grupos funcionales capaces de interaccionar con los precursores de las nanopartículas. Una vez finalizado el proyecto se puede afirmar que se han logrado parte de los objetivos planteados inicialmente. Concreamente ha quedado demostrado que se pueden sintetizar nanopartículas metálicas de metales nobles (platino y paladio) en membranas de fibra hueca de micro- y ultrafiltración siguiendo dos metodologías diferentes: modificación fotoquímica de polímeros y deposición de multicapas de polielectrolitos. Los nuevos materiales son efectivos en la catálisis de reducción de un compuesto modelo (4-nitrofenol con borohidruro de sodio) y, en general, los resultados han sido satisfactorios. Sin embargo, se ha puesto de manifiesto que el uso de un reactivo que genera hidrógeno gas en contacto con la solución acuosa dificulta enormemente la implementación de la reacción catalítica al ser el medio de la membrana una matriz porosa. Así, como conclusión principal se puede decir que se han encontrado las limitaciones de esta aproximación y se sugieren dos posibilidades de continuidad: la utilización de las membranas sintetizadas en contactores gas-líquido o bien el estudio y optimización del sistema de membrana en configuración de membranas planas, un objetivo más asequible dada su menor complejidad. Esta investigación se ha realizado en el seno del “Laboratoire de Génie Chimique” de Toulouse y del Departamento de Química de la Michigan State University y ha sido posible gracias a un proyecto financiado por la “Agence National pour la Recherce” y al programa PERMEANT entre el CNRS y la NSF.

Functionalization of microstructured open-porous bioceramic scaffolds with human fetal bone cells.

Bone substitute materials allowing trans-scaffold migration and in-scaffold survival of human bone-derived cells are mandatory for development of cell-engineered permanent implants to repair bone defects. In this study, we evaluated the influence on human bone-derived cells of the material composition and microstructure of foam scaffolds of calcium aluminate. The scaffolds were prepared using a direct foaming method allowing wide-range tailoring of the microstructure for pore size and pore openings. Human fetal osteoblasts (osteo-progenitors) attached to the scaffolds, migrated across the entire bioceramic depending on the scaffold pore size, colonized, and survived in the porous material for at least 6 weeks. The long-term biocompatibility of the scaffold material for human bone-derived cells was evidenced by in-scaffold determination of cell metabolic activity using a modified MTT assay, a repeated WST-1 assay, and scanning electron microscopy. Finally, we demonstrated that the osteo-progenitors can be covalently bound to the scaffolds using biocompatible click chemistry, thus enhancing the rapid adhesion of the cells to the scaffolds. Therefore, the different microstructures of the foams influenced the migratory potential of the cells, but not cell viability. Scaffolds allow covalent biocompatible chemical binding of the cells to the materials, either localized or widespread integration of the scaffolds for cell-engineered implants.

Placental growth factor contributes to micro-vascular abnormalization and blood-retinal barrier breakdown in diabetic retinopathy.

OBJECTIVE: There are controversies regarding the pro-angiogenic activity of placental growth factor (PGF) in diabetic retinopathy (DR). For a better understanding of its role on the retina, we have evaluated the effect of a sustained PGF over-expression in rat ocular media, using ciliary muscle electrotransfer (ET) of a plasmid encoding rat PGF-1 (pVAX2-rPGF-1). MATERIALS AND METHODS: pVAX2-rPGF-1 ET in the ciliary muscle (200 V/cm) was achieved in non diabetic and diabetic rat eyes. Control eyes received saline or naked plasmid ET. Clinical follow up was carried out over three months using slit lamp examination and fluorescein angiography. After the control of rPGF-1 expression, PGF-induced effects on retinal vasculature and on the blood-external barrier were evaluated respectively by lectin and occludin staining on flat-mounts. Ocular structures were visualized through histological analysis. RESULTS: After fifteen days of rPGF-1 over-expression in normal eyes, tortuous and dilated capillaries were observed. At one month, microaneurysms and moderate vascular sprouts were detected in mid retinal periphery in vivo and on retinal flat-mounts. At later stages, retinal pigmented epithelial cells demonstrated morphological abnormalities and junction ruptures. In diabetic retinas, PGF expression rose between 2 and 5 months, and, one month after ET, rPGF-1 over-expression induced glial activation and proliferation. CONCLUSION: This is the first demonstration that sustained intraocular PGF production induces vascular and retinal changes similar to those observed in the early stages of diabetic retinopathy. PGF and its receptor Flt-1 may therefore be looked upon as a potential regulatory target at this stage of the disease.

Les pintures murals de la basílica de "Es Cap des Port" (Fornells, Menorca): materials i tècniques

El present treball ofereix una revisió de les pintures murals de la basílica de «Es Cap des Port» (Fornells, Menorca), així com un estudi de caracterització arqueometrica deIs materials i tecniques per microscopia optica, tant amb lupa binocular com amb micro scopi petrografic mitjanliant ¡¡lmina prima, difracció de raigs X i microscopia electronica de rastreig. Els resultats han permes identificar els pigments emprats, així com la seva tecnica d'aplicació. Igua!ment, han permes caracteritzar els morters i han desvelat l' existencia de dos tipus diferents de suporto Malgrat aquestes diferencies en els morters, els pigments són sempre els mateixos per a tots els conjunts pictorics caracteritzats.

Role of structural saturation and geometry in the luminescence of silicon-based nanostructured materials

The structural saturation and stability, the energy gap, and the density of states of a series of small, silicon-based clusters have been studied by means of the PM3 and some ab initio (HF/6-31G* and 6-311++G**, CIS/6-31G* and MP2/6-31G*) calculations. It is shown that in order to maintain a stable nanometric and tetrahedral silicon crystallite and remove the gap states, the saturation atom or species such as H, F, Cl, OH, O, or N is necessary, and that both the cluster size and the surface species affect the energetic distribution of the density of states. This research suggests that the visible luminescence in the silicon-based nanostructured material essentially arises from the nanometric and crystalline silicon domains but is affected and protected by the surface species, and we have thus linked most of the proposed mechanisms of luminescence for the porous silicon, e.g., the quantum confinement effect due to the cluster size and the effect of Si-based surface complexes.

Si3N4 single-crystal nanowires grown from silicon micro- and nanoparticles near the threshold of passive oxidation

A simple and most promising oxide-assisted catalyst-free method is used to prepare silicon nitride nanowires that give rise to high yield in a short time. After a brief analysis of the state of the art, we reveal the crucial role played by the oxygen partial pressure: when oxygen partial pressure is slightly below the threshold of passive oxidation, a high yield inhibiting the formation of any silica layer covering the nanowires occurs and thanks to the synthesis temperature one can control nanowire dimensions

Theoretical Analysis and Simulations of Vertically Vibrated Granular Materials

The dynamical properties ofshaken granular materials are important in many industrial applications where the shaking is used to mix, segregate and transport them. In this work asystematic, large scale simulation study has been performed to investigate the rheology of dense granular media, in the presence of gas, in a three dimensional vertical cylinder filled with glass balls. The base wall of the cylinder is subjected to sinusoidal oscillation in the vertical direction. The viscoelastic behavior of glass balls during a collision, have been studied experimentally using a modified Newton's Cradle device. By analyzing the results of the measurements, using numerical model based on finite element method, the viscous damping coefficient was determinedfor the glass balls. To obtain detailed information about the interparticle interactions in a shaker, a simplified model for collision between particles of a granular material was proposed. In order to simulate the flow of surrounding gas, a formulation of the equations for fluid flow in a porous medium including particle forces was proposed. These equations are solved with Large Eddy Simulation (LES) technique using a subgrid-model originally proposed for compressible turbulent flows. For a pentagonal prism-shaped container under vertical vibrations, the results show that oscillon type structures were formed. Oscillons are highly localized particle-like excitations of the granular layer. This self-sustaining state was named by analogy with its closest large-scale analogy, the soliton, which was first documented by J.S. Russell in 1834. The results which has been reportedbyBordbar and Zamankhan(2005b)also show that slightly revised fluctuation-dissipation theorem might apply to shaken sand, which appears to be asystem far from equilibrium and could exhibit strong spatial and temporal variations in quantities such as density and local particle velocity. In this light, hydrodynamic type continuum equations were presented for describing the deformation and flow of dense gas-particle mixtures. The constitutive equation used for the stress tensor provides an effective viscosity with a liquid-like character at low shear rates and a gaseous-like behavior at high shear rates. The numerical solutions were obtained for the aforementioned hydrodynamic equations for predicting the flow dynamics ofdense mixture of gas and particles in vertical cylindrical containers. For a heptagonal prism shaped container under vertical vibrations, the model results were found to predict bubbling behavior analogous to those observed experimentally. This bubbling behavior may be explained by the unusual gas pressure distribution found in the bed. In addition, oscillon type structures were found to be formed using a vertically vibrated, pentagonal prism shaped container in agreement with computer simulation results. These observations suggest that the pressure distribution plays a key rolein deformation and flow of dense mixtures of gas and particles under vertical vibrations. The present models provide greater insight toward the explanation of poorly understood hydrodynamic phenomena in the field of granular flows and dense gas-particle mixtures. The models can be generalized to investigate the granular material-container wall interactions which would be an issue of high interests in the industrial applications. By following this approach ideal processing conditions and powder transport can be created in industrial systems.

Modeling the transport phenomena within arterial wall: porous media approach

The transport of macromolecules, such as low-density lipoprotein (LDL), and their accumulation in the layers of the arterial wall play a critical role in the creation and development of atherosclerosis. Atherosclerosis is a disease of large arteries e.g., the aorta, coronary, carotid, and other proximal arteries that involves a distinctive accumulation of LDL and other lipid-bearing materials in the arterial wall. Over time, plaque hardens and narrows the arteries. The flow of oxygen-rich blood to organs and other parts of the body is reduced. This can lead to serious problems, including heart attack, stroke, or even death. It has been proven that the accumulation of macromolecules in the arterial wall depends not only on the ease with which materials enter the wall, but also on the hindrance to the passage of materials out of the wall posed by underlying layers. Therefore, attention was drawn to the fact that the wall structure of large arteries is different than other vessels which are disease-resistant. Atherosclerosis tends to be localized in regions of curvature and branching in arteries where fluid shear stress (shear rate) and other fluid mechanical characteristics deviate from their normal spatial and temporal distribution patterns in straight vessels. On the other hand, the smooth muscle cells (SMCs) residing in the media layer of the arterial wall respond to mechanical stimuli, such as shear stress. Shear stress may affect SMC proliferation and migration from the media layer to intima. This occurs in atherosclerosis and intimal hyperplasia. The study of blood flow and other body fluids and of heat transport through the arterial wall is one of the advanced applications of porous media in recent years. The arterial wall may be modeled in both macroscopic (as a continuous porous medium) and microscopic scales (as a heterogeneous porous medium). In the present study, the governing equations of mass, heat and momentum transport have been solved for different species and interstitial fluid within the arterial wall by means of computational fluid dynamics (CFD). Simulation models are based on the finite element (FE) and finite volume (FV) methods. The wall structure has been modeled by assuming the wall layers as porous media with different properties. In order to study the heat transport through human tissues, the simulations have been carried out for a non-homogeneous model of porous media. The tissue is composed of blood vessels, cells, and an interstitium. The interstitium consists of interstitial fluid and extracellular fibers. Numerical simulations are performed in a two-dimensional (2D) model to realize the effect of the shape and configuration of the discrete phase on the convective and conductive features of heat transfer, e.g. the interstitium of biological tissues. On the other hand, the governing equations of momentum and mass transport have been solved in the heterogeneous porous media model of the media layer, which has a major role in the transport and accumulation of solutes across the arterial wall. The transport of Adenosine 5´-triphosphate (ATP) is simulated across the media layer as a benchmark to observe how SMCs affect on the species mass transport. In addition, the transport of interstitial fluid has been simulated while the deformation of the media layer (due to high blood pressure) and its constituents such as SMCs are also involved in the model. In this context, the effect of pressure variation on shear stress is investigated over SMCs induced by the interstitial flow both in 2D and three-dimensional (3D) geometries for the media layer. The influence of hypertension (high pressure) on the transport of lowdensity lipoprotein (LDL) through deformable arterial wall layers is also studied. This is due to the pressure-driven convective flow across the arterial wall. The intima and media layers are assumed as homogeneous porous media. The results of the present study reveal that ATP concentration over the surface of SMCs and within the bulk of the media layer is significantly dependent on the distribution of cells. Moreover, the shear stress magnitude and distribution over the SMC surface are affected by transmural pressure and the deformation of the media layer of the aorta wall. This work reflects the fact that the second or even subsequent layers of SMCs may bear shear stresses of the same order of magnitude as the first layer does if cells are arranged in an arbitrary manner. This study has brought new insights into the simulation of the arterial wall, as the previous simplifications have been ignored. The configurations of SMCs used here with elliptic cross sections of SMCs closely resemble the physiological conditions of cells. Moreover, the deformation of SMCs with high transmural pressure which follows the media layer compaction has been studied for the first time. On the other hand, results demonstrate that LDL concentration through the intima and media layers changes significantly as wall layers compress with transmural pressure. It was also noticed that the fraction of leaky junctions across the endothelial cells and the area fraction of fenestral pores over the internal elastic lamina affect the LDL distribution dramatically through the thoracic aorta wall. The simulation techniques introduced in this work can also trigger new ideas for simulating porous media involved in any biomedical, biomechanical, chemical, and environmental engineering applications.

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

The singular properties of hydrogenated amorphous carbon (a-C:H) thin filmsdeposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithographypatterns (in-plane anisotropy). Finally, self-assembly properties were tested with silicananoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

Síntese de sulfadiazina e sulfadiazina de prata em escala semi-micro: prática experimental em síntese de fármacos

The total synthesis of sulfadiazine and silver sulfadiazine from readily available starting materials was adapted to semi-micro laboratory scale and is proposed as an experiment in drug synthesis for undergraduate courses.