Estudo da cura e do comportamento reológico de sistemas poliméricos altamente reforçados em estereolitografia

Mestrado em engenharia de polímerosFruto do aumento da exigência dos consumidores e de novas imposições dos mercados internacionais, o processo de desenvolvimento de um produto sofreu uma profunda alteração com o objectivo de dar resposta à necessidade crescente de produtos mais complexos e de maior qualidade, assim como, da necessidade dos produtos serem lançados no mercado de forma cada vez mais rápida Com vista a cumprir os requisitos anteriores e sendo a estereolitografia uma importante tecnologia de prototipagem rápida destinada à obtenção de protótipos em resina termoendurecível, várias tem sido as estratégias propostas para a obtenção de modelos físicos. A fabricação de protótipos por estereolitografia envolve uma transformação de resinas líquidas por acção de radiação, através de mecanismos de polimerização. Deste modo o trabalho de investigação descrito nesta tese passou pelo estudo de sistemas híbridos envolvendo mecanismos de polimerização radicalar e catiónica e a utilização de cargas metálicas. Foi efectuado um intenso estudo experimental no sentido de conhecer a cinética de cura e o comportamento reológico destes sistemas poliméricos. Vários parâmetros foram objecto de estudo: intensidade de radiação, concentração de iniciador, granolumetria dos pós metálicos. Os resultados obtidos no estudo são particularmente promissoras no que respeita à utilização de resinas reforçadas em aplicações estereolitográficas.The increasing emphasis on consumers’ expectations together with the modern demands of international markets has triggered a deep change on the product development process in order to answer to the growing need of more complex and higher quality products, as well to speed time to market. The concurrent need to respond to these requirements and to develop prototypes in thermosetting resins has conducted to an extensive research on the different strategies used to develop physical models, being Stereolithography one of the most important technologies. The fabrication of rapid prototypes by Stereolithography involves the conversion of liquid resins, through polymerisation mechanisms, by radiation effects. This research work concerns the study of hybrid systems comprising mechanisms of radical and cationic polymerisation and the use of metallic particles. It involved an extensive experimental work to get a better understanding of the cure kinetics and the rheological behaviour of these polymeric systems. Several parameters were investigated like the radiation intensity, the initiator concentration and the granulometry of metallic powders. The findings of this work are particularly important to the use of reinforced resins in stereolithographic applications

Biomimetic design and fabrication of tissue engineered scaffolds using computer aided tissue engineering

The field of tissue engineering brings together the multidisciplinary research of life sciences and engineering to seek man-made substitutes for the regeneration of damaged tissue or organs. A key component in tissue engineering is the use of porous scaffolds to guide cells for attachment, proliferation and differentiation in the tissue regenerative process. Upon satisfactory in-vitro culture, this engineered living scaffold is implanted into the regeneration site of the patient to function as the tissue substitute. Conventional processing techniques for the fabrication of scaffolds often encounter difficulties in the precise control of the internal architecture, interconnectivity and distribution of pores within the scaffold. These challenges, along with the advances in biology, medicine, and information technology for tissue engineering applications, have led to the development of a new field of Computer Aided Tissue Engineering (CATE).CATE enables a systematic application of computer-aided technologies, i.e., computer-aided design (CAD), image processing, computer-aided manufacturing (CAM), and solid freeform fabrication (SFF) for modeling, designing, simulation, and manufacturing of biological tissue and organ substitutes. Through the use of CATE, the design of intricate three dimensional architecture of scaffold can be realized and these scaffolds can be fabricated with reproducible accuracy to assist biologists in studying complex tissue engineering problems. This thesis reports a research addressing some of the challenges in applying the CATE approach for the biomimetic design and freeform fabrication of tissue scaffolds. The major research accomplishments reported in this thesis include: a) The development of a BioCAD modeling technique for the design and representation of patient specific 3D tissue models based on non-invasive medical image data. b) The development of a biomimetic design approach for design of load bearing tissue scaffold subject to multiple biophysical, geometrical and manufacturing requirements. This includes the design of the unit cell micro-architecture based on tissue morphologies, unit cell characterization and evaluation of the mechanical and transport properties, and the use of unit cells as building block to design anatomic tissue scaffold replacements. c) The development of a CAD based path planning procedure through a direct slicing algorithm which can convert a neutral ISO (International Standards Organization) standardized STEP (Standard for the Exchange of Product Data) formatted NURBS (Non-Uniform Rational B-Spline) geometric representation to a tool path instruction set for layered freeform fabrication. d) The development of a novel Internal Architecture Design (IAD) approach for the mapping of characteristic patterns of the unit cell micro-architectures designed within the 3D scaffold. This design approach is implemented into a process algorithm that converts these 2D patterns to tool path datasets for the 3DP™ (threedimensional printing) and extrusion based freeform fabrication.CATE enables many novel approaches in modeling, design, and fabrication of complex tissue substitutes with enhanced functionality for research in patient specific implant analysis and simulation, image guided surgical planning and scaffold guided tissue engineering. The research will also enable cell biologists and engineers to expand their scope of research and study in the field of tissue engineering and regenerative medicine.Ph.D., Mechanical Engineering -- Drexel University, 200

Surface Remeshing and Applications

Due to the focus of popular graphic accelerators, triangle meshes remain the primary representation for 3D surfaces. They are the simplest form of interpolation between surface samples, which may have been acquired with a laser scanner, computed from a 3D scalar field resolved on a regular grid, or identified on slices of medical data. Typical methods for the generation of triangle meshes from raw data attempt to lose as less information as possible, so that the resulting surface models can be used in the widest range of scenarios. When such a general-purpose model has to be used in a particular application context, however, a pre-processing is often worth to be considered. In some cases, it is convenient to slightly modify the geometry and/or the connectivity of the mesh, so that further processing can take place more easily. Other applications may require the mesh to have a pre-defined structure, which is often different from the one of the original general-purpose mesh. The central focus of this thesis is the automatic remeshing of highly detailed surface triangulations. Besides a thorough discussion of state-of-the-art applications such as real-time rendering and simulation, new approaches are proposed which use remeshing for topological analysis, flexible mesh generation and 3D compression. Furthermore, innovative methods are introduced to post-process polygonal models in order to recover information which was lost, or hidden, by a prior remeshing process. Besides the technical contributions, this thesis aims at showing that surface remeshing is much more useful than it may seem at a first sight, as it represents a nearly fundamental step for making several applications feasible in practice

Computational Topology Methods for Shape Modelling Applications

This thesis deals with computational topology, a recent branch of research that involves both mathematics and computer science, and tackles the problem of discretizing the Morse theory to functions defined on a triangle mesh. The application context of Morse theory in general, and Reeb graphs in particular, deals with the analysis of geometric shapes and the extraction of skeletal structures that synthetically represents shape, preserving the topological properties and the main morphological characteristics. Regarding Computer Graphics, shapes, that is a one-, two- or higher- dimensional connected, compact space having a visual appearance, are typically approximated by digital models. Since topology focuses on the qualitative properties of spaces, such as the connectedness and how many and what type of holes it has, topology is the best tool to describe the shape of a mathematical model at a high level of abstraction. Geometry, conversely, is mainly related to the quantitative characteristics of a shape. Thus, the combination of topology and geometry creates a new generation of tools that provide a computational description of the most representative features of the shape along with their relationship. Extracting qualitative information, that is the information related to semantic of the shape and its morphological structure, from discrete models is a central goal in shape modeling. In this thesis a conceptual model is proposed which represents a given surface based on topological coding that defines a sketch of the surface, discarding irrelevant details and classifying its topological type. The approach is based on Morse theory and Reeb graphs, which provide a very useful shape abstraction method for the analysis and structuring of the information contained in the geometry of the discrete shape model. To fully develop the method, both theoretical and computational aspects have been considered, related to the definition and the extension of the Reeb graph to the discrete domain. For the definition and automatic construction of the conceptual model, a new method has been developed that analyzes and characterizes a triangle mesh with respect to the behavior of a real and at least continuous function defined on the mesh. The proposed solution handles also degenerate critical points, such as non-isolated critical points. To do that, the surface model is characterized using a contour-based strategy, recognizing critical areas instead of critical points and coding the evolution of the contour levels in a graph-like structure, named Extended Reeb Graph, (ERG), which is a high-level abstract model suitable for representing and manipulating piece-wise linear surfaces. The descriptive power of the (ERG) has been also augmented with the introduction of geometric information together with the topological ones, and it has been also studied the relation between the extracted topological and morphological features with respect to the real characteristics of the surface, giving and evaluation of the dimension of the discarded details. Finally, the effectiveness of our description framework has been evaluated in several application contexts

Surface slicing algorithm based on topology transition

Presented in this paper is an algorithm to compute the intersections of a parametric regular surface with a set of parallel planes. Rather than using an ordinary surface-plane intersection algorithm repeatedly, we pre-process a surface to identify points, called topology transition points (TTP's), on the surface where the topologies of intersection curves change. It turns out that such points can be computed efficiently, exactly and robustly employing a normal surface, and they are categorized into seven distinct groups. Analyzing the properties of such characteristic points on the surface, the starting points to trace intersection curves can be found rather efficiently and robustly. Such intersection contours can be used in various applications including rapid prototyping, solid freeform fabrication, process planning