Desenvolvimento de método para análise e identificação das propriedades de materiais biológicos

• Autor(a) principal: Maciejewski, Narco Afonso Ravazzoli
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações do UNIOESTE
• Texto Completo: http://tede.unioeste.br/handle/tede/3993
• topic: Coloproctologia; Cicatrização; Elasticidade Tecidual; Reologia; Coloproctology; Healing; Tissue Elasticity; Rheology; CIRURGIA::CIRURGIA PROCTOLOGICA

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.