Publicación: Silicona de moldeo como sustituto mecánico para tejido biológico
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2024-10-22
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Universidad Nacional de Educación a Distancia (España), Universidad de Concepción - Chile. Departamento de Ingeniería Mecánica
Resumen
En diversas disciplinas como la investigación forense, la industria balística y la biomecánica, es de gran interés encontrar un sustituto artificial para el tejido vivo que permita realizar pruebas experimentales, recreando, según la aplicación, propiedades térmicas, eléctricas, ópticas, acústicas y mecánicas. Para este fin, se han utilizado diferentes materiales como sustitutos, entre los cuales destacan las suspensiones líquidas, las gelatinas, los elastómeros, las resinas epoxi, los metales y los textiles, no obstante, solo las gelatinas y los elastómeros pueden tener un comportamiento mecánico similar al tejido vivo, generalmente viscoelástico y en muchos casos, hiper elástico.
El presente trabajo tiene como objetivo recrear las propiedades mecánicas a tracción y compresión del tejido uterino para una gestaste promedio, enfatizando en que no se han documentado materiales sustitutos con propiedades mecánicas similares al útero. El material sustituto se requiere para ser implementado en un modelo dinámico experimental de útero grávido artificial que contempla las estructuras del feto, el útero y el líquido amniótico, y que permite estudiar la cinemática fetal durante el embarazo. La silicona estudiada será empleada para la piel del feto y el recubrimiento interior del modelo uterino que, a diferencia del gel balístico, es químicamente estable en medios acuosos, con alta durabilidad y termo estabilidad, características que ayudan a la ejecución de los ensayos experimentales y reducen la variabilidad de las propiedades mecánicas del material por agentes externos. Se ejecutó la caracterización mecánica en tracción y compresión de una silicona de moldeo con dureza shore 30A. La obtención de las probetas se realizó con base en la metodología de Chanda, mezclando en partes iguales la base polimérica con el agente de curado, para posterior vertimiento la mezcla en moldes impresos de ácido poli láctico flexible (PLA +) con la geometría negativa de las probetas. Se ensayaron cinco velocidades de deformación (0.5, 0.72, 3.6, 24 y 90 min-1) para los ensayos de tracción y una velocidad de deformación (0.5 min-1) en los ensayos de compresión, mediante la fractura controlada de las probetas en una máquina de ensayos universal MTS Bionix. Las gráficas de esfuerzo real vs deformación real, así como esfuerzo real vs estiramiento muestran un comportamiento hiper elástico no lineal. Se realizaron ajustes polinómicos de séptimo orden para cada set de datos (R > 0.98) con los cuales se compararon estadísticamente las velocidades de deformación ensayadas (p > 0.05). Al comparar los resultados del comportamiento a tracción de la silicona, se observó un ajuste satisfactorio con los datos experimentales presentados en la literatura. El comportamiento a compresión de la silicona difiere con respecto al del tejido biológico, mostrando mayor rigidez en el rango ensayado, lo cual puede atribuirse al ordenamiento aleatorio de las fibras de colágeno en el tejido uterino (miometrio) cuando es sometido a cargas compresivas. Se ajustó el modelo de Veronda–Westmann para el comportamiento hiper elástico no lineal de la silicona mediante el método de mínimos cuadrados, respaldando la practicidad de este modelo para tejido biológico. Se concluye que la silicona ensayada puede ser utilizada como sustituto experimental del tejido uterino sometido a cargas de tracción y compresión, aclarando que en cargas compresivas el sustituto produciría deformaciones menores a las reales. Por otro lado, las constantes ajustadas en el modelo hiper elástico de Veronda-Westmann permiten estudiar la respuesta uterina en diferentes escenarios de interés mediante simulación computacional.
Depending on the application, it is of great interest in various disciplines such as forensic research, the ballistics industry and biomechanics to find an artificial substitute for living tissue that allows experimental tests to be performed, recreating thermal, electrical, optical, acoustic and mechanical properties. For this purpose, different materials have been used as substitutes, mainly liquid suspensions, gelatines, elastomers, epoxy resins, metals and textiles, however, only gelatines and elastomers can have a mechanical behavior close to living tissue, generally viscoelastic and, in many cases, hyper elastic. The present work aims to recreate the tensile and compressive mechanical properties of uterine tissue for an average gestation, emphasizing that no surrogate materials with mechanical properties analogous to the uterus have been documented. The surrogate material is required to be implemented in an experimental dynamic model of artificial pregnant uterus that considers the structures of the fetus, the uterus and the amniotic fluid, and that allows the study of fetal kinematics during pregnancy. The silicone studied will be used for the skin of the fetus and the inner lining of the uterine model which, unlike the ballistic gel, is chemically stable in aqueous media, with high durability and thermal stability, characteristics that help the execution of the experimental tests and reduce the vulnerability of the mechanical properties of the material to external agents. The mechanical characterization in tension and compression of a molding silicone with shore hardness 30A was carried out. The specimens were obtained based on the methodology of Chanda, mixing in equal parts the polymeric base with the curing agent, and then pouring the mixture into printed molds of flexible poly lactic acid (PLA +) with the negative geometry of the specimens. Five strain rates (0.5, 0.72, 3.6, 24 y 90 min-1) for tensile tests and one strain rate (0.5 min-1) for compression tests were tested by controlled fracture of the specimens in an MTS Bionix universal testing machine. The plots of true stress vs true strain, as well as true stress vs stretch show a non-linear hyper elastic behavior. When comparing the tensile behavior results of silicone, a satisfactory fit with the experimental data presented in the literature was observed. The compression behavior of silicone differs from that of biological tissue, showing higher stiffness in the range tested, which can be attributed to the random arrangement of collagen fibers in the uterine tissue (myometrium) when subjected to compressive loads. The Veronda-Westmann model was fitted for the nonlinear hyper elastic behavior of silicone by means of the least squares method, supporting the practicality of this model for biological tissue. It is concluded that the tested silicone can be used as an experimental substitute for uterine tissue subjected to tensile and compressive loads, clarifying that in compressive loads the substitute would produce smaller deformations than the real ones. On the other hand, the adjusted constants in the hyper elastic Veronda-Westmann model allow studying the uterine response in different situations of interest through computer simulation.
Depending on the application, it is of great interest in various disciplines such as forensic research, the ballistics industry and biomechanics to find an artificial substitute for living tissue that allows experimental tests to be performed, recreating thermal, electrical, optical, acoustic and mechanical properties. For this purpose, different materials have been used as substitutes, mainly liquid suspensions, gelatines, elastomers, epoxy resins, metals and textiles, however, only gelatines and elastomers can have a mechanical behavior close to living tissue, generally viscoelastic and, in many cases, hyper elastic. The present work aims to recreate the tensile and compressive mechanical properties of uterine tissue for an average gestation, emphasizing that no surrogate materials with mechanical properties analogous to the uterus have been documented. The surrogate material is required to be implemented in an experimental dynamic model of artificial pregnant uterus that considers the structures of the fetus, the uterus and the amniotic fluid, and that allows the study of fetal kinematics during pregnancy. The silicone studied will be used for the skin of the fetus and the inner lining of the uterine model which, unlike the ballistic gel, is chemically stable in aqueous media, with high durability and thermal stability, characteristics that help the execution of the experimental tests and reduce the vulnerability of the mechanical properties of the material to external agents. The mechanical characterization in tension and compression of a molding silicone with shore hardness 30A was carried out. The specimens were obtained based on the methodology of Chanda, mixing in equal parts the polymeric base with the curing agent, and then pouring the mixture into printed molds of flexible poly lactic acid (PLA +) with the negative geometry of the specimens. Five strain rates (0.5, 0.72, 3.6, 24 y 90 min-1) for tensile tests and one strain rate (0.5 min-1) for compression tests were tested by controlled fracture of the specimens in an MTS Bionix universal testing machine. The plots of true stress vs true strain, as well as true stress vs stretch show a non-linear hyper elastic behavior. When comparing the tensile behavior results of silicone, a satisfactory fit with the experimental data presented in the literature was observed. The compression behavior of silicone differs from that of biological tissue, showing higher stiffness in the range tested, which can be attributed to the random arrangement of collagen fibers in the uterine tissue (myometrium) when subjected to compressive loads. The Veronda-Westmann model was fitted for the nonlinear hyper elastic behavior of silicone by means of the least squares method, supporting the practicality of this model for biological tissue. It is concluded that the tested silicone can be used as an experimental substitute for uterine tissue subjected to tensile and compressive loads, clarifying that in compressive loads the substitute would produce smaller deformations than the real ones. On the other hand, the adjusted constants in the hyper elastic Veronda-Westmann model allow studying the uterine response in different situations of interest through computer simulation.
Descripción
Organizado y patrocinado por: Federación iberoamericana de Ingeniería Mecánica y Universidad de Concepción - Chile. Departamento de Mecánica, FeIbIm – FeIbEM
Categorías UNESCO
Palabras clave
Tejido uterino, Elasticidad no lineal, Caracterización mecánica, Silicona de moldeo, Hiper elasticidad, Uterine tissue, Nonlinear elasticity, Mechanical characterization, Molding silicone, Hyper elasticity
Citación
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E.T.S. de Ingenieros Industriales
Departamento
Mecánica