# Research Progress in the Construction and Application of In Vitro Vascular Models
## 4 Summary and Prospects
Additionally, the type of culture medium, serum concentration, and external environment can also influence the model. Furthermore, there is a lack of standardized characterization and stability evaluation methods for in vitro models, leading to a lack of reproducibility, which hinders their widespread use. When it comes to cell types, primary cells are closer to the human physiological environment compared to immortal cell lines. However, the cost of culturing primary cells is high, and the availability of materials is limited. Moreover, as primary cells undergo more passages, their tight junctions weaken, resulting in increased permeability that affects model stability. Therefore, it is crucial to improve experimental techniques, select high-quality serum and culture media, and optimize cell cryopreservation and resuscitation procedures. In the process of constructing vascular models, there are two additional challenges: cellular spatial arrangement and maintaining uniform distribution [130; 131]. Firstly, cellular spatial arrangement involves effectively organizing and arranging various cell types such as endothelial cells, smooth muscle cells, and other supporting cells to simulate the complex structure and functions of real blood vessels. This requires precise control over cell positions and relationships to ensure the model accurately reflects the physiological characteristics of the vascular system. Secondly, maintaining a uniform distribution of cells is another key issue. In three-dimensional space, the uniformity of cell distribution directly affects the stability and reproducibility of the model. Uneven distribution can lead to localized metabolic and signaling abnormalities, thereby impacting the interpretation of experimental results and the application value of models. To address these challenges, advanced cell culture techniques and microfluidic systems are typically relied upon to precisely control cell positioning and environmental conditions. These technologies not only facilitate uniform cell distribution but also enhance model complexity and physiological relevance, providing a reliable platform and tool for the development of vascular models used in drug screening and disease research. Although in vitro vascular models are generally more physiologically relevant than two-dimensional models, they still struggle to replicate the complex metabolic conditions of the human body. As a result, their physiological relevance and clinical applicability have not been fully investigated and proven. Current complex in vitro models consist of single or multiple tissues and organs, but integrating all these components to simulate specific physiological functions remains a major challenge due to difficulties and high costs. Additionally, it is challenging to replicate the differences in blood pressure, flow rate, and dynamic components across different parts of the complex in vitro model, making it difficult for vascular models to fully replicate the in vivo environment. The vascular models discussed in this article are reusable through perfusion devices, and the endothelial cells in the pipeline are on materials with good biocompatibility, which can simulate the microenvironment of blood vessels and three-dimensional cellular tissues in vivo. Additionally, these models are reproducible in shape and length, enabling repeated experiments that are difficult to conduct with natural blood vessels. However, due to technical limitations, current engineered vascular models can only last for a few weeks, limiting their use in the early stages of acute and chronic diseases. Therefore, it is important to focus on improving the long-term stability of in vitro vascular models, which can be reflected in endothelial homeostasis, perfusion capacity, permeability, and contractility of blood vessels. Furthermore, current models primarily use cell lines that can be used alone or in combination with different cells.