Development and validation of a failure model of the healthy porcine intestine

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Gastrointestinal perforations (GIPs) lead to high mortality and usually require emergency surgeries. They are associated with high mortality, especially when diagnosed and treated late. Since neither experimental studies nor numerical models are available to describe GIPs, the underlying mechanics have remained largely unexplained. This research project therefore aims to, (i) understand for the first time the fundamental mechanical processes that occur during a GIP through layer-specific experiments under both active and passive conditions, and (ii) describe and predict them for the first time using a numerical three-dimensional model that will be calibrated and validated based on these experiments. To achieve this goal, intestinal tissue from healthy pigs will be used, as it is structurally and functionally similar to human intestinal tissue. The preparations will be examined both biomechanically and histologically in order to identify microstructural and mechanical properties from position-dependent information. Firstly, experiments are performed on tissue strips to characterise passive and active tissue properties. This includes classical uniaxial and biaxial experiments in the undamaged state as well as various experiments up to failure. In particular, the failure properties of the individual tissue layers and their components are analysed. On the other hand, the intestinal wall structure is recorded in histological and structural analyses. Based on this knowledge and an already existing model, which in its current form only takes into account the purely passive failure behaviour of the overall wall structure, an activation-dependent, layer-specific failure model of the healthy pig intestine is developed. This includes a detailed description of the layered microstructure of the intestinal tissue, including kinematic nonlinearity, anisotropic properties, incompressibility, and interfacial behaviour, incorporating a variation-based phase field modelling approach for damage and fractures. Through this comprehensive computational model, GIPs in the small and large intestine are described quantitatively. The model will be calibrated and validated at the tissue strip scale. As a result of this project, the world's first biomechanical, layer-specific model for the description of GIPs will be available, thus creating the basis for the clinical utilisation of the knowledge gained in the project in future work, especially with respect to human tissue. A special feature of the model developed in this project will be its strong basis in experimental data, whereas the currently available failure models for soft tissues of any kind are insufficiently supported by test data.