Submitted by Wagner Junior (wagner.junior@unioeste.br) on 2018-10-30T19:51:43Z No. of bitstreams: 2 referencia.pdf: 27563 bytes, checksum: 74f45da034fcc5757becd278cfad8b50 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-10-30T19:51:43Z (GMT). No. of bitstreams: 2 referencia.pdf: 27563 bytes, checksum: 74f45da034fcc5757becd278cfad8b50 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-03-06 / Information derived from the analysis of the mechanical behavior of biological tissues increases the efficiency of diagnosis, as well as of clinical and surgical treatments. The importance of this resides in the fact that, in many organs such as the colon, the rupture of tissues is associated with high rates of morbidity and mortality. In this context, several mechanical tests are used to evaluate the mechanical resistance of biological tissues. However, most of the existing tests are susceptible to criticism, since these materials have microstructures with heterogeneous and anisotropic characteristics. In this way, based on the knowledge that the majority of biological tissues present a non-linear viscoelastic mechanical behavior, a new method was proposed in this work for the analysis and identification of the properties of these materials. The proposed method aims to analyze curves generated by means of mechanical traction tests of biological tissues under constant speed. Its originality is based on the mathematical modeling of these tissues behavior and the discretization of the function in three regions, which are characterized by elastic, elastoplastic and leakage periods. This methodological process enabled to detect constants of proportionality in the elastic and elastoplastic regions, denominated as tissue elasticity (KT ) and tissue stiffness (KR). The proposed method was applied to a case study using data derived from descending colon segments of 20 rats, obtained through the Total Energy of Rupture (ETR) biomechanical test. Initially, the mathematical modeling was performed with the Boltzmann sigmoidal model for all curves. Then, with these adjustments, the coefficients of determination of each function were calculated, along with its average and respective standard deviation (R2 = 0, 9975 +/- 0; 0021). After these procedures,the curve, in its integrality, was discretized by first and second order numerical derivation for each point of the curve. Then the elastic regions were determined, and the mean relative to the remainder of the curve was calculated (6; 9120 +/- 1; 2577%), as well as the mean of the constant KT (34; 5437 +/- 3; 7547gf=cm). The same procedure was performed for the elastoplastic regions (mean = 89; 3334 +/- 5; 3974% and the KR = 87; 8945 +/- 8; 1226gf=cm). After these procedures, it was possible to construct a standard curve, with lower and upper limits, to describe the mechanical behavior of the intestinal rings of rats with the average Boltzmann model parameters for each curve. According to the criteria evaluated, the proposed method for the analysis and identification of non-linear viscoelastic materials properties showed to be accurate and reliable, as the mechanical properties of these materials were fully analyzed employing the method proposed in this work. / Informações provenientes da análise do comportamento mecânico de tecidos biológicos proporcionam o aumento da eficiência de diagnósticos e de tratamentos clínicos e cirúrgicos. A importância disso está no fato de que em muitos órgãos, como o cólon, a ruptura de seus tecidos está associada a altos índices de morbidade e mortalidade. Nesse contexto, diversos ensaios mecânicos são utilizados para avaliar a resistência mecânica de tecidos biológicos. No entanto, grande parte dos testes existentes são passíveis de críticas, pois esses materiais possuem microestruturas com características heterogêneas e anisotrópicas. Desse modo, com o conhecimento de que a maioria dos tecidos biológicos apresentam comportamento mecânico viscoelástico não linear, foi proposto um novo método para a análise e a identificação das propriedades desses materiais. O método proposto tem como objetivo analisar as curvas geradas por meio de ensaios mecânicos de tração sob velocidade constante de tecidos biológicos e a originalidade está fundamentada na modelagem matemática e na discretização da função em três regiões, caracterizadas pelos períodos elástico, elastoplástico e de escoamento do comportamento desses tecidos. Assim, foi possível detectar nas regiões elástica e elastoplástica constantes de proporcionalidade, sendo estas denominadas elasticidade tecidual (KT ) e rigidez tecidual (KR), respectivamente. Um estudo de caso foi realizado com dados provenientes de segmentos de cólon descendente de 20 ratos, obtidos por meio do ensaio biomecânico Energia Total de Ruptura (ETR). Inicialmente, a modelagem matemática foi realizada com o modelo sigmoidal de Boltzmann para todas as curvas, e, com esses ajustes, foram então calculados os coeficientes de determinação de cada função e a sua média com o respectivo desvio padrão (R2 = 0, 9975+/-0; 0021). Posteriormente, a curva, na sua integralidade, foi discretizada por meio da derivação numérica de primeira e de segunda ordem para cada ponto da mesma, e, assim, as regiões elásticas foram determinadas e a média calculada (6, 9120+/-1; 2577%) em relação ao restante da curva, assim como a média da constante KT (34, 5437 +/- 3; 7547gf=cm). O mesmo procedimento foi aplicado para as regiões elastoplásticas alcançando a média de 89, 3334 +/- 5; 3974% e o KR = 87, 8945 +/- 8; 1226gf=cm. Após, foi possível a construção de uma curva padrão, com os limites inferior e superior, para descrever o comportamento mecânico de alças intestinais de ratos com a média dos parâmetros do modelo de Boltzmann para cada curva. Sendo assim, de acordo com os critérios avaliados, o método proposto para a análise e identificação das propriedades de materiais viscoelásticos não lineares se mostrou preciso e confiável, pois as propriedades mecânicas desses materiais foram integralmente analisadas por meio do método proposto nesse trabalho.

Numerous eye diseases are linked to biomechanical dysfunction of the retina. However, the underlying forces are almost impossible to quantify experimentally. Here, we show how biomechanical properties of adult neuronal tissues such as porcine retinae can be investigated under tension in a home-built tissue stretcher composed of nanostructured TiO2 scaffolds coupled to a self-designed force sensor. The employed TiO2 nanotube scaffolds allow for organotypic long-term preservation of adult tissues ex vivo and support strong tissue adhesion without the application of glues, a prerequisite for tissue investigations under tension. In combination with finite element calculations we found that the deformation behavior is highly dependent on the displacement rate which results in Young’s moduli of (760–1270) Pa. Image analysis revealed that the elastic regime is characterized by a reversible shear deformation of retinal layers. For larger deformations, tissue destruction and sliding of retinal layers occurred with an equilibration between slip and stick at the interface of ruptured layers, resulting in a constant force during stretching. Since our study demonstrates how porcine eyes collected from slaughterhouses can be employed for ex vivo experiments, our study also offers new perspectives to investigate tissue biomechanics without excessive animal experiments.