Characterization of biaxial mechanical properties of rubber and skin

textBreast cancer is one of the most frequently diagnosed cancers affecting women in the United States. An ongoing objective of many research groups is to develop a biomechanical breast model for different applications, ranging from surgical outcome predictions for patients undergoing breast reconstruction surgery, to image registration for planning plastic surgery. Achieving the goal of developing a physics based biomechanical model of the human breast requires the determination of material properties of the various tissues constituting the breast. The objective of this thesis is to develop an appropriate hybrid experimental-numerical technique to enable the calibration of material parameters of skin for different constitutive models (commonly used for skin). The quantification of the material parameters thus obtained validates the bulge test method to be used in testing soft tissue specimens like skin. A bulge test device was custom-built for this work; it consists of a pressure chamber, two digital cameras, and a syringe pump as its main components. The syringe pump provides a constant flow rate of water into the pressure chamber and results in the bulging of specimens with a diameter between 45 mm and 80 mm. Three-dimensional Digital Image Correlation technique is used to obtain full field displacement measurements of the three dimensional shape of the bulge. Tests were performed on commercial rubber sheets of different thickness and on porcine skin specimens; in these tests, the bulge shape was measured at monotonically increasing and decreasing pressure levels, as well as during cyclic loading allowing determination of the deformation and strain fields over the specimen surface. In order to extract the material properties, a hybrid experimental-numerical method was used: the experiment was modeled numerically using the finite element analysis software Abaqus, imposing the commonly used Mooney-Rivlin model for isotropic materials and the Gasser-Ogden-Holzapfel model for anisotropic materials. A comparison between the experimentally measured and numerically simulated bulge shapes was used to determine the optimized material parameters under biaxial loading conditions over a large range of stretch levels.Biomedical Engineerin

Simulação analítica da deformação de superfícies com realismo : estudo de caso do olho humano

Dissertação (mestrado)–Universidade de Brasília, Faculdade UnB de Planaltina, Programa de Pós-Graduação em Ciência de Materiais, 2017.Este trabalho apresenta a simulação analítica utilizada para deformação de superfícies esféricas preenchidas com líquido em seu interior com realismo físico. A solução analítica aqui desenvolvida garante o realismo físico e a preservação de volume em superfícies fechadas cheias de liquido. Implementamos esta solução analítica em realidade virtual que foi aplicada a um modelo tridimensional do olho humano. O modelo do olho é aproximado de uma superfície fechada cheia de líquido e com volume constante. Através da utilização de ambiente virtual, deformamos a superfície do olho, com a simulação, visualização e interação tátil tridimensional. A simulação consiste na aplicação de força sobre a superfície do olho, que por sua vez pode ser manipulado e deformado com a utilização de uma plataforma gráfica. Já as imagens serão geradas por meio da utilização de um monitor de computador, com isso, obtemos sensações visuais. O retorno de força (sensações táteis) em tempo real é obtido por meio da manipulação do dispositivo háptico virtual. O presente trabalho de mestrado está em consonância com uma tendência mundial que é a busca de ferramentas eficientes com uso de simuladores para a educação, aperfeiçoamento, treinamento médico, processos de tomada de decisão em pré-cirurgias e cirurgias guiadas por imagem. Podemos a partir desse trabalho, como aplicação futura, desenvolver simuladores com execução em tempo real aceitável, uma vez que o modelo apresentado demonstra-se eficiente para aplicações médicas e biológicas utilizando a tecnologia de realidade virtual com a finalidade de ensino em procedimentos cirúrgicos e de diagnóstico de patologias.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).This work focuses on the analytical solution for presentation filled spherical surfaces with or without liquid. The analytical solution developed here guarantees physical realism and the preservation of volume on closed surfaces filled with liquid. We implemented this virtual reality analytical solution that was applied to a three-dimensional model of the human eye. The model of the eye is approximated to a closed surface filled with liquid and with a constant volume. Through the use of virtual environment, we deform the surface of the eye, with simulation, visualization and tactile three-dimensional interaction. The simulation consists of the application of force on the surface of the eye, which in turn can be manipulated and deformed using a graphic platform. The images will be generated through the use of a computer monitor, with this, we obtain visual and tactile sensations. The real-time force return is obtained through the manipulation of the virtual haptic device. This project is in line with a global trend that is the search for effective tools to use simulators for education, improvement and medical training, decision-making processes in pre-surgeries and imageguided surgeries. From this work, as a future application, we can develop simulators with acceptable real-time execution, since the model presented is efficient for medical and biological applications using virtual reality technology for the purpose of teaching surgical procedures and diagnosis of pathologies.Este trabajo presenta la simulación analítica utilizada para deformación de superficies esféricas rellenadas con líquido en su interior con realismo físico. La solución analítica aquí desarrollada garantiza el realismo físico y la preservación de volumen en superficies cerradas llenas de líquido. Hemos implementado esta solución analítica en realidad virtual que se ha aplicado a un modelo tridimensional del ojo humano. El modelo del ojo es aproximado a una superficie cerrada llena de líquido y con volumen constante. A través del uso de ambiente virtual, deformamos la superficie del ojo, con la simulación, visualización e interacción táctil tridimensional. La simulación consiste en la aplicación de fuerza sobre la superficie del ojo, que a su vez puede ser manipulada y deformada con la utilización de una plataforma gráfica. Las imágenes se generarán mediante el uso de un monitor de ordenador, con lo que obtenemos sensaciones visuales. El retorno de fuerza (sensaciones táctiles) en tiempo real se obtiene por medio de la manipulación del dispositivo háptico virtual. El presente trabajo de maestría está en consonancia con una tendencia mundial que es la búsqueda de herramientas eficientes con uso de simuladores para la educación, perfeccionamiento, entrenamiento médico, procesos de toma de decisión en precirugía y cirugías guiadas por imagen. Podemos a partir de ese trabajo, como aplicación futura, desarrollar simuladores con ejecución en tiempo real aceptable, una vez que el modelo presentado se demuestra eficientemente para aplicaciones médicas y biológicas utilizando la tecnología de realidad virtual con la finalidad de enseñanza en procedimientos quirúrgicos y de diagnóstico de patologías

Soft volume simulation using a deformable surface model

The aim of the research is to contribute to the modelling of deformable objects, such as soft tissues in medical simulation. Interactive simulation for medical training is a concept undergoing rapid growth as the underlying technologies support the increasingly more realstic and functional training environments. The prominent issues in the deployment of such environments centre on a fine balance between the accuracy of the deformable model and real-time interactivity. Acknowledging the importance of interacting with non-rigid materials such as the palpation of a breast for breast assessment, this thesis has explored the physics-based modelling techniques for both volume and surface approach. This thesis identified that the surface approach based on the mass spring system (MSS) has the benefits of rapid prototyping, reduced mesh complexity, computational efficiency and the support for large material deformation compared to the continuum approach. However, accuracy relative to real material properties is often over looked in the configuration of the resulting model. This thesis has investigated the potential and the feasibility of surface modelling for simulating soft objects regardless of the design of the mesh topology and the non-existence of internal volume discretisation. The assumptions of the material parameters such as elasticity, homogeneity and incompressibility allow a reduced set of material values to be implemented in order to establish the association with the surface configuration. A framework for a deformable surface model was generated in accordance with the issues of the estimation of properties and volume behaviour corresponding to the material parameters. The novel extension to the surface MSS enables the tensile properties of the material to be integrated into an enhanced configuration despite its lack of volume information. The benefits of the reduced complexity of a surface model are now correlated with the improved accuracy in the estimation of properties and volume behaviour. Despite the irregularity of the underlying mesh topology and the absence of volume, the model reflected the original material values and preserved volume with minimal deviations. Global deformation effect which is essential to emulate the run time behaviour of a real soft material upon interaction, such as the palpation of a generic breast, was also demonstrated, thus indicating the potential of this novel technique in the application of soft tissue simulation

Soft volume simulation using a deformable surface model

The aim of the research is to contribute to the modelling of deformable objects, such as soft tissues in medical simulation. Interactive simulation for medical training is a concept undergoing rapid growth as the underlying technologies support the increasingly more realstic and functional training environments. The prominent issues in the deployment of such environments centre on a fine balance between the accuracy of the deformable model and real-time interactivity. Acknowledging the importance of interacting with non-rigid materials such as the palpation of a breast for breast assessment, this thesis has explored the physics-based modelling techniques for both volume and surface approach. This thesis identified that the surface approach based on the mass spring system (MSS) has the benefits of rapid prototyping, reduced mesh complexity, computational efficiency and the support for large material deformation compared to the continuum approach. However, accuracy relative to real material properties is often over looked in the configuration of the resulting model. This thesis has investigated the potential and the feasibility of surface modelling for simulating soft objects regardless of the design of the mesh topology and the non-existence of internal volume discretisation. The assumptions of the material parameters such as elasticity, homogeneity and incompressibility allow a reduced set of material values to be implemented in order to establish the association with the surface configuration. A framework for a deformable surface model was generated in accordance with the issues of the estimation of properties and volume behaviour corresponding to the material parameters. The novel extension to the surface MSS enables the tensile properties of the material to be integrated into an enhanced configuration despite its lack of volume information. The benefits of the reduced complexity of a surface model are now correlated with the improved accuracy in the estimation of properties and volume behaviour. Despite the irregularity of the underlying mesh topology and the absence of volume, the model reflected the original material values and preserved volume with minimal deviations. Global deformation effect which is essential to emulate the run time behaviour of a real soft material upon interaction, such as the palpation of a generic breast, was also demonstrated, thus indicating the potential of this novel technique in the application of soft tissue simulation.EThOS - Electronic Theses Online ServiceUniversiti Malaysia Sarawak (UMS)Malaysia. Jabatan Perkhidmatan Awam (JPA)Malaysia. Kementerian Pengajian Tinggi (KPT)GBUnited Kingdo