ProcessModelling - Process-oriented maturation model of biohybrid heart valves during bioreactor conditioning

组织工程心脏瓣膜（TEHV）是一种很有前途的心脏瓣膜替代方法。所谓的生物杂交植入物包括一个提供机械强度的纺织支架，上面覆盖着嵌入水凝胶的患者自己的细胞，这些细胞能够再生并适应周围的环境。这种人工心脏瓣膜的成熟过程是在生物反应器中进行的，在生物反应器中，心脏瓣膜由脉动的培养基流灌注。这个过程涉及复杂的动力学，不仅取决于作用于心脏瓣膜的外部刺激，还取决于所用组织形成细胞的个体生长参数。因此，长期的研究目标是对个体成熟过程的鲁棒性和适应性控制，以生产生物相容性和弹性的植入物。对于这样的控制方案，必须知道成熟过程的潜在动力学。在这个项目的第一阶段，我们确定了描述组织成熟过程的输入、状态和输出变量之间的关键关系。在此基础上，我们建立了组织成熟的数学模型。该模型包含细胞数量的演变以及以胶原蛋白和弹性蛋白为代表的细胞外基质的发育，因为它们对心脏瓣膜小叶的结构和力学特性至关重要。为了验证模型，建立了一个生物反应器装置，用于自动化、可重复和可比较的成熟实验，包括用于非破坏性和纵向组织观察的多光子内窥镜显微镜。进行了多次实验以获得工艺知识并验证了我们的模型。在PAK ii阶段，重点将从tev成熟过程的开环控制转向闭环控制。基于第一阶段获得的关于组织成熟控制的见解，生物反应器的设置将扩展到其他控制概念（WP1）。对于状态变量的在线观测，将实现双光子内窥镜图像采集和数据分析例程（WP2）。基于第一阶段成熟过程的数学模型、新开发的生物反应器、双光子内窥镜的实现以及基于图像的成熟分析结果，我们将建立一个基于模型的过程控制方案（WP3）。这些改进将与成熟实验密切相关，迭代地测试系统并收集工艺验证的数据（WP4）。通过这个项目，我们对主动脉TEHV的闭环成熟控制有了明确的了解，从而在考虑到心脏瓣膜高度个性化的同时，实现了这些植入物的稳健生产。在该项目中获得的见解也可转移到其他生物杂交结构，如组织工程血管移植物和贴片，以及其他非心血管组织工程植入物。

Tissue-engineered heart valves (TEHV) are a promising approach in the area of heart valve replacement. So-called biohybrid implants consist of a textile scaffold providing mechanical strength covered with patient-own cells embedded in a hydrogel, which are able to regenerate and adapt their surroundings. The maturation process of such artificial heart valves is performed in a bioreactor, in which the heart valve is perfused by a pulsating flow of culture media. This process involves complex dynamics, which depend not only on external stimuli acting on the heart valve, but also on the individual growth parameters of the tissue-forming cells used. Thus, the longterm research goal is the robust and adaptive control of the individual maturation process for the production of biocompatible and resilient implants. For such a control scheme, the underlying dynamics of the maturation process must be known. In phase I of this project, we identified the key relationships between input, state, and output variables of the process that describe tissue maturation. Based on this, we developed a mathematical model of tissue maturation. The model contains the evolution of the cell number as well as the development of the extracellular matrix represented by the proteins collagen and elastin, as they are crucial for the architecture and mechanical characteristics of heart valve leaflets. For the model validation, a bioreactor setup for automated and thus reproducible and comparable maturation experiments was established including multiphoton endoscopic microscopy for non-destructive and longitudinal tissue observation. Multiple experiments were performed to gain process knowledge and validate our model. In PAK phase-II, the focus will move from open-loop control of the maturation process of TEHV towards closed-loop control. Based on the insights about tissue maturation control gained in phase I, the bioreactor setup will be expanded with additional control concepts (WP1). For the online observation of the state variables, two-photon endoscopy image acquisition and data analysis routines will be implemented (WP2). Building on the results of phase I regarding our mathematical model of the maturation process, the newly developed bioreactor, implementation of two-photon endoscopy, and the image-based analysis of maturation, we will establish a model-based control scheme for the process (WP3). These improvements will be closely related to maturation experiments, iteratively testing the system and collecting data for process validation (WP4). With this project, we acquire an explicit understanding of closed-loop maturation control of aortic TEHV, leading towards a robust production of these implants while considering the high degree of heart valve individuality. The insights gained in this project are also transferrable to other biohybrid constructs such as tissue engineered vascular grafts and patches, as well as other non-cardiovascular tissue engineered implants.