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

胃肠道穿孔(GIP)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的时候。由于既没有实验研究，也没有数值模型来描述GIPS，其基本机制在很大程度上仍未得到解释。因此，本研究项目的目标是：(I)通过主动和被动条件下的特定层级实验，首次了解GIP过程中发生的基本力学过程，以及(Ii)首次使用将在这些实验基础上校准和验证的数值三维模型来描述和预测它们。为了实现这一目标，将使用来自健康猪的肠道组织，因为它在结构和功能上与人类肠道组织相似。将从生物力学和组织学两个方面对制备的材料进行检查，以便根据位置相关信息确定微观结构和机械性能。首先，在组织条上进行实验，以表征被动和主动组织属性。这包括未受损状态下的经典单轴和双轴实验，以及直到失效的各种实验。具体地，分析了各个组织层及其组分的破坏特性。另一方面，在组织学和结构分析中记录了肠壁结构。基于这一认识和已有的模型(其当前形式仅考虑整个肠壁结构的纯被动失效行为)，开发了健康猪肠的激活依赖、特定于层的失效模型。这包括对肠道组织的层状微结构的详细描述，包括运动非线性、各向异性、不可压缩性和界面行为，并结合了用于损伤和骨折的基于变化的相场建模方法。通过这个综合计算模型，定量描述了小肠和大肠中的GIPs。该模型将在组织条尺度上进行校准和验证。作为这一项目的结果，世界上第一个描述GIPS的生物力学特定层模型将可用，从而为在未来的工作中临床使用在该项目中获得的知识创造基础，特别是关于人体组织的知识。本项目开发的模型的一个特点是其强大的实验数据基础，而目前可用的任何类型软组织的破坏模型都没有足够的实验数据来支持。

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.