For the finite element (FE) simulation of relatively thin organs under complex dynamic loadings that are relevant in the biomedical engineering field, shell elements, compared to volume elements, have the potential to capture the whole thickness of the organ at once. Shell elements, are also known to feature efficiently large critical time steps, ensuring competitive computational times in dynamic structural analysis projects. As an improvement to the tools available for modelling and analysis, a new general nonlinear thick continuum-based (CB) shell FE embedded in an updated Lagrangian formulation and an explicit time integration scheme was recently developed. It can account for irregular and complex geometries, and hyper-elastic, large, nearly incompressible anisotropic 3D deformations characteristic of soft tissues. The original proof of concept was developed in MATLAB, which despite known advantages, is very slow. As a result, computational times, even for simple problems, have not been competitive. Therefore, the present work focused on re-writing the code in an efficient programming language with execution speed in mind in order to compete with the available elements which, in spite of having inferior capabilities, have better running times. In addition, a programming algorithm was needed to improve running time. Once it was implemented, the running time was reduced in half on a benchmark problem. Optimization was then exploited to introduce workarounds and design improvements that reduced running time further to 95% of its original value. The new version of the code was implemented in C++ and reached the goal of reducing running time while maintaining the expected functionality.

Biological materials are complex hierarchical systems subjected to external stimuli like mechanical forces, chemical potentials and electrical signals. A deeper understanding of the behavior of these materials is required for the response characterization of healthy and diseased conditions. The primary aim of this dissertation is to study the mechanics of biological materials like cells and tissues from a computational perspective and relate its behavior with experimental works, so as to provide a framework for the identification and treatment of pathological conditions like cancer and vascular diseases. The first step towards understanding the behavior of a biological cell is to comprehend its response to external mechanical stimuli. Experimentally derived material properties of cells have found to vary by orders of magnitude even for the same cell type. The primary cause of such disparity is attributed to the stimulation process, and the theoretical models used to interpret the experimental data. The variations in mechanical properties obtained from the experimental and theoretical studies can be overcome only through the development of a sound mathematical framework correlating the derived mechanical property with the cellular structure. Such a formulation accounting for the inhomogeneity of the cytoplasm due to stress fibers and actin cortex is developed in this work using Mori-Tanaka method of homogenization. Mechanical modeling of single cells would be extremely useful in understanding its behavior in an experimental setup. Characterization of in-vivo response of cells requires mathematical modeling of the embedding environment like fibers and fluids, which forms the extra cellular matrix. Studies on fluid-tissue interactions in biomechanics have primarily relied on either an iterative solution of the individual solid or tissue phases or a sequential solution of the entire domain using a coupled algorithm. In this dissertation, a new computational methodology for the analysis of fluid-tissue interaction problem is presented. The modeling procedure is based on a biphasic representation of fluid and tissue domain, consisting of fluid and solid phases. The biphasic-fluid interaction model is also implemented to study the transfer of low-density lipoprotein from the blood to the arterial wall, and also the nutrient transfer in the tissue scaffolds of a bioreactor.

No description available.

Exploring the mechanical properties of soft tissues under compressive loading is crucial for understanding their role in automobile incidents. Soft tissues, which serve as cushions or padding between bone and vehicle interiors, significantly influence contact duration and forces, thereby altering incident kinematics and injury risk assessment. In this investigation, muscle and soft connective tissues from post-mortem human subjects (PMHS) forearms were excised and subjected to compression and indentation testing methods at various rates and strains. Anthropomorphic Test Devices (ATDs) upper extremity foam and vinyl foam composite material surrogate tissues underwent similar testing for comparison. High impact rates simulating those in high-speed car collisions were achieved using a custom-built drop tower. The results revealed substantial differences in stiffness between soft tissues and ATD materials across most loading rates and strains, although some exceptions were noted at higher rates and strains. Indentation and modified Zener models were used to quantify material parameters. The indentation model could characterize human muscle, soft connective tissues and ATD vinyl foam composites, but fell short with ATD foam materials. The Zener model effectively derived material parameters for the tested human tissues but encountered difficulties characterizing both ATD materials. This highlights the need for further refinement to develop a constitutive model for both materials. These findings provide a solid basis for advancing ATD surrogate materials and have broader implications for soft tissue research. Moreover, this work represents a crucial step towards enhancing safety standards in the automotive industry. / Thesis / Master of Science in Biomedical Engineering / Soft tissues are crucial in mitigating impact effects in various loading scenarios, yet their specific roles are complex and poorly understood. Understanding soft tissues' role in these loading scenarios is critical for understanding injury risk tolerances. This study aimed to characterize muscle and soft connective tissue behaviour during compressive loading scenarios using various techniques and modelling approaches. This was done through compressive loading tests on soft tissues and comparing these same tests with data from current crash test dummy surrogate tissues. The results showed that the soft tissues were less stiff than the crash test dummy materials in most scenarios. It was also apparent that different stiffnesses were seen depending on soft connective tissue and muscle tissue composition. This study provides insights into the rate dependence of materials, alongside the relevance of how different compositions affect their loading properties. This characterization also revealed significant discrepancies between the responses of current surrogates and human muscle and soft connective tissues. This work offers valuable observations and data for refining ATD surrogates and enhancing their fidelity in simulating real-world impact scenarios. Such advancements are pivotal for improving safety standards.

Introduction: Though xenogeneic acellular scaffolds are frequently used for surgical reconstruction, knowledge of their mechanical properties is lacking. This study compared the mechanical, histological and ultrastructural properties of various native and acellular specimens. Materials and methods: Porcine esophagi, ureters and skin were tested mechanically in a native or acellular condition, focusing on the elastic modulus, ultimate tensile stress and maximum strain. The testing protocol for soft tissues was standardized, including the adaption of the tissue’s water content and partial plastination to minimize material slippage as well as templates for normed sample dimensions and precise cross-section measurements. The native and acellular tissues were compared at the microscopic and ultrastructural level with a focus on type I collagens. Results: Increased elastic modulus and ultimate tensile stress values were quantified in acellular esophagi and ureters compared to the native condition. In contrast, these values were strongly decreased in the skin after acellularization. Acellularization-related decreases in maximum strain were found in all tissues. Type I collagens were well-preserved in these samples; however, clotting and a loss of cross-linking type I collagens was observed ultrastructurally. Elastins and fibronectins were preserved in the esophagi and ureters. A loss of the epidermal layer and decreased fibronectin content was present in the skin. Discussion: Acellularization induces changes in the tensile properties of soft tissues. Some of these changes appear to be organ specific. Loss of cross-linking type I collagen may indicate increased mechanical strength due to decreasing transverse forces acting upon the scaffolds, whereas fibronectin loss may be related to decreased load-bearing capacity. Potentially, the alterations in tissue mechanics are linked to organ function and to the interplay of cells and the extracellular matrix, which is different in hollow organs when compared to skin.

As aves representam a grande maioria das espécies da fauna silvestre mantidas como animais de companhia em nosso meio e respondem diretamente pela crescente demanda pelo atendimento médico veterinário. O avanço na área da anestesiologia viabilizou a realização de procedimentos cirúrgicos mais longos e complexos e contribuiu para o desenvolvimento e aprimoramento da técnica operatória em aves, contudo, dados nacionais de casuística relacionados às afecções cirúrgicas de aves ainda são inexistentes. Assim, este estudo avaliou retrospectivamente as operações realizadas em aves no Serviço de Cirurgia de Pequenos Animais do Hospital Veterinário da Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, entre janeiro de 2000 a junho de 2008, com o objetivo de identificar as afecções cirúrgicas, apresentar sua ocorrência e distribuição de freqüência segundo as ordens e espécies acometidas, avaliar as técnicas operatórias empregadas e comparar os dados obtidos com os achados da literatura. De um total de 90 operações realizadas para diagnóstico e/ou tratamento de afecções, 27 foram ortopédicas e 63 de tecidos moles. Quanto ao percentual de operações ortopédicas realizadas segundo as diferentes ordens, observou-se: Psittaciformes 85,19%, Piciformes 7,41%, Anseriformes 3,70% e Falconiformes 3,70%. Para as operações de tecidos moles os psitaciformes representaram 92,06%, columbiformes 3,17%, passeriformes 3,17% e anseriformes 1,59%. Entre os tipos de afecções ortopédicas encontradas as fraturas apresentaram a maior ocorrência (88,89%), seguidas de luxação (3,70%), avulsão traumática de extremidade (3,70%) e artrite/osteomielite (3,70%), o membro pélvico foi o mais acometido e o tibiotarso o osso mais fraturado. Dentre as afecções cirúrgicas de tecidos moles as neoplasias apresentaram a maior ocorrência (30,16%), seguida das neoformações cutâneas ou de anexos não neoplásicos (17,46%), neoformações cutâneas sem diagnóstico (7,94%), distocia (7,94%), fístula de papo (7,94%), hérnia abdominal (4,76%), sinusite (4,76%), gangrena de extremidade de membros (3,17%), perfuração de esôfago (3,17%), prolapso de cloaca (3,17%), Necrose avascular de dígito (1,59%), ferida na região da quilha (1,59%), perfuração de cavidade celomática (1,59%), neoformação em cavidade celomática sem diagnóstico (1,59%), corpo estranho em trato gastrointestinal (1,59%) e otite (1,59%). O lipoma foi a neoplasia e o cáseo a neoformação não neoplásica mais freqüentes. A distribuição das afecções cirúrgicas segundo as espécies acometidas mostrou o grupo dos papagaios, representado em sua maioria por espécies do gênero Amazona, como prevalente. A fixação interna com pino intramedular foi a técnica operatória mais utilizada nas afecções cirúrgicas ortopédicas e apresentou elevado índice de retorno à função para tratamento das fraturas. A exérese foi a técnica operatória mais utilizada nas afecções cirúrgicas de tecidos moles e mostrou índices elevados de cura e baixa ocorrência de recidivas. O conhecimento das afecções cirúrgicas e das espécies de aves mais acometidas, bem como dos resultados obtidos com as técnicas operatórias empregadas, acrescentam informações para aqueles que já atuam nesta área e servem como indicador de estudo para futuros cirurgiões de aves / Birds represent one of the main wildlife species kept as pets in our country and respond directly by the growing demand for health care veterinarian. Advancement in the field of anesthesiology has enabled the surgical procedures longer and more complex and contributed to the development and refinement of surgical technique in birds. However, national data series related to surgical disorders in birds are still poor. This study assessed retrospectively the avian operations at the Service of Small Animal Surgery - Veterinary Hospital of the School of Veterinary Medicine and Animal Science of the University of São Paulo, from January 2000 to June 2008. The focus was to identify the surgical disorders, occurrence and frequency distribution according to orders and species affected, also we evaluated the surgical techniques employed and compared the results with the literature findings. A total of 90 operations were performed for diagnosis or treatment of surgical disorders. Of these 27 were orthopedic and 63 soft tissue surgeries. Considering the orthopedic surgeries performed according to orders we observed: Psittaciformes 85,19%, Piciformes 7,41%, Anseriformes 3,70% and Falconiformes 3,70%. And for the soft tissues operations the Psittaciformes represented 92,06%, Columbiformes 3,17%, Passeriformes 3,17% and Anseriformes 1,59%. Fractures presented the highest incidence among orthopedic disorders (88,89%), followed by luxation (3,70%), traumatic avulsion of the end (3,70%) and arthritis/osteomyelitis (3,70%). The pelvic limb was the most affected member and the tibiotarsus was the most commonly fractured bone. Among the surgical disorders of soft tissue, neoplasms accounted for 30,16%, followed by cutaneous neoformation or annexes nonneoplastic (17,46%), cutaneous neoformations undiagnosed (7,94%), dystocia (7,94%), fistula crop (7,94%), abdominal hernia (4,76%), sinusitis (4,76%), gangrene of the extremity members (3,17%), esophageal perforation (3,17%), prolapse of cloaca (3,17%), \"avascular necrosis of digit (1,59%), wound in the region of the keel (1,59%), perforation of the coelomic cavity (1,59%), neoformation in the coelomic cavity without a diagnosis (1,59%), foreign body in the gastrointestinal tract (1,59%) and otitis (1,59%). Lipoma and caseous were the most frequent cancer and non-neoplastic neoformation observed, respectively. The distribution of surgical disorders according to species affected showed that the \"group of parrots\", mainly represented by species of Amazonas genus, was prevalent. Internal fixation with intramedullary pin was the technique most often used in orthopedic surgical disorders and showed a high rate of recovery of limb function. The excision was the technique mostly used in the surgical disorders of soft tissue and presented high rates of cure and low recurrence. Knowledge of surgical and bird species most affected, and the results obtained with the surgical techniques employed, add information for those who works in this area and will be an indicator for future surgeons of birds

O propósito do presente estudo foi avaliar, radiograficamente, a relação entre lábios, pogônio mole, maxila, mandíbula e incisivos em indivíduos com perfil facial equilibrado. Foram avaliados 30 brasileiros do gênero feminino, entre 19 e 31 anos de idade, dos quais foram obtidas telerradiografias em norma lateral, na posição natural da cabeça orientada. A análise cefalométrica foi realizada avaliando-se o nariz, os lábios e o pogônio mole em relação à linha vertical verdadeira que passa pelo ponto subnasal (SnV), a maxila e a mandíbula em relação à base do crânio e os incisivos em relação às suas bases ósseas. Os resultados demonstraram que o lábio superior se apresentou ligeiramente à frente da linha SnV, o lábio inferior se posicionou sobre a linha e o pogônio mole atrás da mesma. Já a maxila se apresentou ligeiramente protruída enquanto que a mandíbula encontrou-se bem posicionada em relação à base do crânio, deste modo, a relação maxílo-mandibular se mostrou um pouco aumentada. Embora os incisivos superiores tenham apresentado inclinações normais, os inferiores se encontraram ligeiramente vestibularizados. Foram, também, observadas correlações positivas estatisticamente significativas entre: o comprimento mandibular e a projeção do lábio inferior; a projeção do pogônio duro e a projeção do pogônio mole; a relação maxilo-mandibular e a relação labial no sentido antero-posterior; a projeção dos lábios e a projeção do pogônio mole. Foi observada, ainda, correlação negativa estatisticamente significativa entre: a inclinação do incisivo inferior e a projeção do lábio inferior; a inclinação do incisivo inferior e a projeção pogônio mole. / The purpose of this study was to radiographically evaluate the relations hip between lips, soft pogonion, maxilla, mandible and incisors in individuals with a balanced facial profile. Thirty Brazilian women aged 19 to 31 years were evaluated, from whom teleradiographs (lateral view) were taken in the natural position of the oriented head. The cephalometric analysis was performed evaluating the nose, the lips and the soft pogonion in relation to the vertical line which passes by the subnasal point (SnV), the maxilla and the mandible in relation to the base of the skull and the incisors in relation to their bone bases. The results demonstrated that the upper lip was slightly forward to SnV line, the lower lip was positioned on the line and the soft pogonion was behind the line. The maxilla was slightly protruded, whereas the mandible waswell positioned in relation to the base of the skull, therefore the maxillomandibular relationship was somewhat augmented. Although the upper incisors had normal inclinations, the lower incisors were slightly protruded. Statistically significant positive correlations were also observed between the mandibular length and the projection of the lower lip; the projection of the hard pogonion and the projection of the soft pogonion; the maxillomandibular relationship and the lip relationship in the anteroposterior direction and between the projection of the lips and the projection of the soft pogonion. A statistically significant negative correlation was also found between the inclination of the lower incisor and the projection of the lower lip and between the inclination of the lower incisor and the projection of the soft pogonion.

As aves representam a grande maioria das espécies da fauna silvestre mantidas como animais de companhia em nosso meio e respondem diretamente pela crescente demanda pelo atendimento médico veterinário. O avanço na área da anestesiologia viabilizou a realização de procedimentos cirúrgicos mais longos e complexos e contribuiu para o desenvolvimento e aprimoramento da técnica operatória em aves, contudo, dados nacionais de casuística relacionados às afecções cirúrgicas de aves ainda são inexistentes. Assim, este estudo avaliou retrospectivamente as operações realizadas em aves no Serviço de Cirurgia de Pequenos Animais do Hospital Veterinário da Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, entre janeiro de 2000 a junho de 2008, com o objetivo de identificar as afecções cirúrgicas, apresentar sua ocorrência e distribuição de freqüência segundo as ordens e espécies acometidas, avaliar as técnicas operatórias empregadas e comparar os dados obtidos com os achados da literatura. De um total de 90 operações realizadas para diagnóstico e/ou tratamento de afecções, 27 foram ortopédicas e 63 de tecidos moles. Quanto ao percentual de operações ortopédicas realizadas segundo as diferentes ordens, observou-se: Psittaciformes 85,19%, Piciformes 7,41%, Anseriformes 3,70% e Falconiformes 3,70%. Para as operações de tecidos moles os psitaciformes representaram 92,06%, columbiformes 3,17%, passeriformes 3,17% e anseriformes 1,59%. Entre os tipos de afecções ortopédicas encontradas as fraturas apresentaram a maior ocorrência (88,89%), seguidas de luxação (3,70%), avulsão traumática de extremidade (3,70%) e artrite/osteomielite (3,70%), o membro pélvico foi o mais acometido e o tibiotarso o osso mais fraturado. Dentre as afecções cirúrgicas de tecidos moles as neoplasias apresentaram a maior ocorrência (30,16%), seguida das neoformações cutâneas ou de anexos não neoplásicos (17,46%), neoformações cutâneas sem diagnóstico (7,94%), distocia (7,94%), fístula de papo (7,94%), hérnia abdominal (4,76%), sinusite (4,76%), gangrena de extremidade de membros (3,17%), perfuração de esôfago (3,17%), prolapso de cloaca (3,17%), Necrose avascular de dígito (1,59%), ferida na região da quilha (1,59%), perfuração de cavidade celomática (1,59%), neoformação em cavidade celomática sem diagnóstico (1,59%), corpo estranho em trato gastrointestinal (1,59%) e otite (1,59%). O lipoma foi a neoplasia e o cáseo a neoformação não neoplásica mais freqüentes. A distribuição das afecções cirúrgicas segundo as espécies acometidas mostrou o grupo dos papagaios, representado em sua maioria por espécies do gênero Amazona, como prevalente. A fixação interna com pino intramedular foi a técnica operatória mais utilizada nas afecções cirúrgicas ortopédicas e apresentou elevado índice de retorno à função para tratamento das fraturas. A exérese foi a técnica operatória mais utilizada nas afecções cirúrgicas de tecidos moles e mostrou índices elevados de cura e baixa ocorrência de recidivas. O conhecimento das afecções cirúrgicas e das espécies de aves mais acometidas, bem como dos resultados obtidos com as técnicas operatórias empregadas, acrescentam informações para aqueles que já atuam nesta área e servem como indicador de estudo para futuros cirurgiões de aves / Birds represent one of the main wildlife species kept as pets in our country and respond directly by the growing demand for health care veterinarian. Advancement in the field of anesthesiology has enabled the surgical procedures longer and more complex and contributed to the development and refinement of surgical technique in birds. However, national data series related to surgical disorders in birds are still poor. This study assessed retrospectively the avian operations at the Service of Small Animal Surgery - Veterinary Hospital of the School of Veterinary Medicine and Animal Science of the University of São Paulo, from January 2000 to June 2008. The focus was to identify the surgical disorders, occurrence and frequency distribution according to orders and species affected, also we evaluated the surgical techniques employed and compared the results with the literature findings. A total of 90 operations were performed for diagnosis or treatment of surgical disorders. Of these 27 were orthopedic and 63 soft tissue surgeries. Considering the orthopedic surgeries performed according to orders we observed: Psittaciformes 85,19%, Piciformes 7,41%, Anseriformes 3,70% and Falconiformes 3,70%. And for the soft tissues operations the Psittaciformes represented 92,06%, Columbiformes 3,17%, Passeriformes 3,17% and Anseriformes 1,59%. Fractures presented the highest incidence among orthopedic disorders (88,89%), followed by luxation (3,70%), traumatic avulsion of the end (3,70%) and arthritis/osteomyelitis (3,70%). The pelvic limb was the most affected member and the tibiotarsus was the most commonly fractured bone. Among the surgical disorders of soft tissue, neoplasms accounted for 30,16%, followed by cutaneous neoformation or annexes nonneoplastic (17,46%), cutaneous neoformations undiagnosed (7,94%), dystocia (7,94%), fistula crop (7,94%), abdominal hernia (4,76%), sinusitis (4,76%), gangrene of the extremity members (3,17%), esophageal perforation (3,17%), prolapse of cloaca (3,17%), \"avascular necrosis of digit (1,59%), wound in the region of the keel (1,59%), perforation of the coelomic cavity (1,59%), neoformation in the coelomic cavity without a diagnosis (1,59%), foreign body in the gastrointestinal tract (1,59%) and otitis (1,59%). Lipoma and caseous were the most frequent cancer and non-neoplastic neoformation observed, respectively. The distribution of surgical disorders according to species affected showed that the \"group of parrots\", mainly represented by species of Amazonas genus, was prevalent. Internal fixation with intramedullary pin was the technique most often used in orthopedic surgical disorders and showed a high rate of recovery of limb function. The excision was the technique mostly used in the surgical disorders of soft tissue and presented high rates of cure and low recurrence. Knowledge of surgical and bird species most affected, and the results obtained with the surgical techniques employed, add information for those who works in this area and will be an indicator for future surgeons of birds

This dissertation introduces a new approach to measure the mechanical properties of soft tissues. A laser-induced microbubble, created by focusing a single nanosecond laser pulse with a custom-made objective lens, was created at desired locations inside a tissue sample. An acoustic radiation force was generated by a low frequency transducer to displace the microbubble. A custom-built high pulse repetition frequency (PRF) ultrasound system, consisting of two 25 MHz single element transducers, was used to track the dynamics of the microbubble. Reconstruction of the mechanical properties at the specific location in a tissue sample was performed using a theoretical model, which calculated the dynamics of a microbubble under an externally applied force in a viscoelastic medium. The theoretical model and the high PRF ultrasound system were successfully validated in both gelatin phantoms and ex vivo bovine crystalline lenses. Age-related sclerosis of the crystalline lenses from bovine was clearly detected, which might be linked to changes in the crystalline. Location-dependent variation explained that the outer cortex and the inner nucleus had different mechanical properties. In the old and young porcine vitreous humors, age-related changes were not found. However, local variations of the mechanical properties were discovered, which may coincide with the different distributions of the molecular compositions. The laser-induced microbubble approach shows potential for future research into the origin of physiological phenomena and the development of inherent disorders in the eye. I hope that further studies – in the development of a more suitable theoretical model for the microbubble dynamics, in extension to in vivo applications, and in defining the relationship of the mechanical properties to molecular components in the eye – may provide a plan for the therapeutic treatment of eye-related diseases. / text

Le projet de thèse concerne la construction, la génération et l'identification de modèles continus stochastiques, pour des milieux hétérogènes exhibant des comportements non linéaires. Le domaine d'application principal visé est la biomécanique, notamment au travers du développement d'outils de modélisation multi-échelles et stochastiques, afin de quantifier les grandes incertitudes exhibées par les tissus mous. Deux aspects sont particulièrement mis en exergue. Le premier point a trait à la prise en compte des incertitudes en mécanique non linéaire, et leurs incidences sur les prédictions des quantités d'intérêt. Le second aspect concerne la construction, la génération (en grandes dimensions) et l'identification multi-échelle de représentations continues à partir de résultats expérimentaux limités / This work is concerned with the construction, generation and identification of stochastic continuum models, for heterogeneous materials exhibiting nonlinear behaviors. The main covered domains of applications are biomechanics, through the development of multiscale methods and stochastic models, in order to quantify the great variabilities exhibited by soft tissues. Two aspects are particularly highlighted. The first one is related to the uncertainty quantification in non linear mechanics, and its implications on the quantities of interest. The second aspect is concerned with the construction, the generation in high dimension and multiscale identification based on limited experimental data