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

胃肠道穿孔（GIPs）导致高死亡率，通常需要紧急手术。它们与高死亡率有关，特别是在诊断和治疗较晚时。由于既没有实验研究也没有数值模型来描述GIPs，其潜在的机制在很大程度上仍然无法解释。因此，本研究项目旨在：(i)通过主动和被动条件下的特定层实验，首次了解GIP期间发生的基本机械过程，（ii）首次使用数值三维模型描述和预测这些过程，该模型将基于这些实验进行校准和验证。为了实现这一目标，将使用健康猪的肠道组织，因为它在结构和功能上与人类肠道组织相似。这些制剂将进行生物力学和组织学检查，以便从位置相关信息中识别微观结构和机械特性。首先，在组织条上进行实验，以表征被动和主动组织的特性。这包括经典的未损伤状态下的单轴和双轴实验，以及各种直至失效的实验。特别地，分析了各个组织层及其组成部分的破坏特性。另一方面，在组织学和结构分析中记录肠壁结构。基于这一知识和已经存在的模型，其目前形式仅考虑整体壁结构的纯被动破坏行为，开发了一个依赖于激活的健康猪肠层特异性破坏模型。这包括对肠组织分层微观结构的详细描述，包括运动学非线性、各向异性、不可压缩性和界面行为，并结合基于变化的相场建模方法来研究损伤和骨折。通过这个综合的计算模型，定量地描述了小肠和大肠的GIPs。该模型将在组织条尺度上进行校准和验证。作为这个项目的结果，世界上第一个生物力学的、用于描述GIPs的特定层的模型将可用，从而为在未来的工作中，特别是在人体组织方面，在项目中获得的知识的临床利用创造基础。在这个项目中开发的模型的一个特点是它有很强的实验数据基础，而目前可用的任何软组织的破坏模型都没有足够的实验数据支持。

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.