Computational foot modeling for clinical assessment

Esta Tesis desarrolla un modelo de elementos finitos del pie humano completo y detallado en tres dimensiones para avanzar hacia una simulación computacional más precisa que proporcione información realista y relevante para la práctica clínica. Desde el punto de vista ingenieril, el pie humano es una compleja estructura de pequeños huesos, soportados por fuertes ligamentos y controlada por una red de músculos y tendones con una capacidad de respuesta mecánica excepcional. La barrera actual en la simulación computacional del pie es la inclusión de estas estructuras musculotendinosas en los modelos. Para avanzar en esta dirección, se crea un modelo de elementos finitos del pie completo y detallado con geometría real de la estructura interna diferenciando hueso cortical y esponjoso, tendón, músculo, cartílago y grasa. Se realizan ensayos experimentales de los tendones del pie y la suela plantar para determinar sus propiedades materiales y estructurales y caracterizar computacionalmente su comportamiento mecánico no lineal. Estos avances están orientados hacia la mejora de la representación geométrica y caracterización del tejido de los componentes internos del pie. El modelo desarrollado en esta Tesis puede usarse en el campo de la biomecánica en áreas de ortopedia, lesiones, tratamiento, cirugía y deporte. La investigación está estructurada por capítulos en los cuales se desarrollan pequeños avances hacia el objetivo principal de la Tesis al mismo tiempo que se aplica el potencial de estos avances a casos particulares. Estas contribuciones parciales en el área de los ensayos experimentales son: la determinación de un completo conjunto de datos de las propiedades mecánicas de los tendones del pie, la definición de un criterio para cuantificar las regiones de la curva de tensión-deformación del tendón y el análisis de la respuesta a compresión de la suela plantar en función de la posición. Y, en el área de la biomecánica clínica las contribuciones son: la investigación de un parámetro del esqueleto como factor etiológico del hallux valgus, el estudio de sensibilidad de la fuerza de los cinco mayores tendones estabilizadores, el análisis cuasi-estático de la fase de apoyo de la marcha y el estudio del mecanismo de absorción de la fuerza de impacto del pie durante la carrera descalzo a diferentes ángulos de impacto.In this Thesis, a complete detailed three-dimensional finite element model of the human foot is described to advance towards a more refined computational simulation which provides realistic and meaningful information for clinical practice. From an engineering perspective, the human foot is a complex structure of small bones supported by strong ligaments and controlled by a network of tendons and muscles that achieves a superb mechanical responsiveness. The current barrier in foot computational simulation is the inclusion of these musculotendinous structures in the models. To advance in this direction, a complete detailed three-dimensional foot finite element model with actual geometry of the inner structure is created differentiating cortical and trabecular bone, tendon, muscle, cartilage and fat tissues. Experimental tests of foot tendons and plantar soles are performed to determine their structural and material properties and to characterize computationally their non-linear mechanical behavior. Those advances are oriented to refine the geometry and the tissue characterization of the internal foot components. The model developed in this Thesis can be used in the field of biomechanics, in the areas of orthopedics, injury, treatment, surgery and sports biomechanics. The research is structured by chapters where small steps towards the main objective are developed and the potential of these advances are applied to particular cases. These partial contributions in the area of the experimental testing are: the determination of a complete dataset of the mechanical properties of the balance foot tendons, the definition of a criteria to quantify the regions of the tendon stress-strain curve and the analysis of the compressive response of plantar soft tissue as function of the location. And, in the area of clinical biomechanics the contributions are: the investigation of a skeletal parameter as etiology factor of the hallux valgus, the tendon force sensitivity study of the five major stabilizer tendons, the quasi-static analysis of the midstance phase of walking and the study of the impact absorption mechanism of the foot during barefoot running at different strike patterns

Investigation of the effect of nozzle design on rheological bioprinting properties using computational fluid dynamics

Bioprinting is the utilization of techniques derived from three-dimensional printing to generate complex biologicalstructures which may replace natural tissues or organs. It employs high spatial resolution depositionof different cell types, growth factors and biomaterials. Those together form bioinks, which are the bioprintinginputs, analogously to conventional inks with regard to inkjet printing. In extrusion bioprinting, continuousbioink filaments are deposited layer by layer on a surface by means of an extruder nozzle, employing thedisplacement of a piston or pneumatic pressure. If mechanical stresses applied on a cell membrane exceed acritical value, which depends on the cell type, the cell membrane may disrupt. Computational fluid dynamics(CFD) simulations of the bioink extrusion were done to evaluate shear stresses caused by the internal pressureof extruder nozzles during bioprinting. Different three-dimensional conical nozzle designs were testedby varying angles of convergence, lengths, input diameters and output diameters of the nozzles. The powerlawmodel, with constants k = 109.73 Pa·s0,154 and n = 0.154, was used to describe the expected non-Newtonian behavior of the bioink. Shear stresses and shear rates were evaluated for each nozzle design consideringdifferent pressures or velocities as boundary conditions at the nozzle entrance. The maximum wallshear stress value on each different nozzle varied between 1,038 Pa and 4,915 Pa. The results indicated whichdetails of nozzle geometry are most relevant in order to optimize bioprinting. The best conditions for bioinkrheology were also evaluated to ensure good printability and high cell viability.Keywords: bioink, bioprinting, biofabrication, 3D printing, CFD

Automation of the process for accessing lip forces

The decrease of lip strength results in the absence of lip contact, which may result in musculature neuromuscular imbalance and affect several functions, such as harmonic dental growth, swallowing, speech and breathing. The measurement of lip strength is an important task in clinical speech pathology practice. This paper describes the development of a measurement system to be used in the processes of force assessment of lips. The user can follow the measurement by means of an interface, which allows registration of information, such as patient personal data, measurement and a brief report. The developed system may be used on personal computer at Windows platfor

Análise das tensões actuantes nas estruturas ósseas bucais provocadas por aparelho com parafuso expansor

Problemas de maloclusão decorrentes de alterações no desenvolvimento das arcadas sãonormalmente encontrados na população. Levam a disfunções na articulação têmporo-mandibular ealterações na mastigação, fala e respiração. Os pacientes necessitam ser tratados precocemente paraque os tratamentos resultem em melhorias funcionais e de estética. Esses distúrbios de crescimentoocasionam uma estética desfavorável que pode afetar a auto-estima dos pacientes. Portadores demaloclusão, nomeadamente crianças e adolescentes, bem como adultos jovens, necessitam detécnicas de tratamento ortodônticas e ortopédicas que permitam a remodelação do contorno ósseo euma melhor arquitetura das arcadas dentais. As técnicas usuais para correções desses distúrbiosrequerem a instalação de aparelhos expansores que impõem deslocamentos graduais peloaccionamento de um parafuso provocando a remodelação óssea conduzindo a uma nova posição deequilíbrio das arcadas. Neste trabalho foram realizadas medições in vivo das forças geradas por umdesses aparelhos para validar simulações computacionais posteriores. Com essas simulações,pretende-se tornar possível uma aplicação de forças menos traumáticas, atenuando sintomasdolorosos como cefaleias, necrose parcial do palato e até a perda de elementos dentais. A primeiraetapa do trabalho envolveu a quantificação de forças provocadas por esses dispositivos e acaracterização do tecido da mucosa da mandíbula com base em ensaios de tração. Posteriormente,utilizando o método de elementos finitos, foram realizadas análises preliminares para obtenção dastensões actuantes nas estruturas ósseas da mandíbula provocadas pelo aparelho expansor, sendo osresultados comparados com os medidos em laboratório e os disponíveis na literatura