# Research Progress in the Construction and Application of In Vitro Vascular Models
## 4 Summary and Prospects
Similarly, microchannels with smaller curvature often maintain better barrier integrity by promoting stable cell-cell connections and reducing the likelihood of cell detachment or disruption. However, while smaller diameters enhance connections and barrier function,spatial and nutrient constraints may limit cell migration and affect cellular vitality. In contrast, larger diameters facilitate cell migration within microchannels but may compromise barrier integrity by allowing looser cell-cell connections. In conclusion, the diameter and curvature of microchannels formed by fabrication methods play a crucial role in the formation of endothelial monolayers, barrier function, cellular vitality, and migration within vascular models. These parameters are indispensable considerations in the design of microfluidic systems for studying vascular biology, drug delivery, and disease modeling. Shear stress and other mechanical factors strongly influence endothelial cells [100]. Fluid flow and shear stress play crucial roles in the construction of vascular models and their biological impacts. Fluid flow not only affects the structural formation of models but also directly influences the function and behavior of cells. Adjusting the speed and direction of fluid can affect the distribution and aggregation of biological materials (such as cells and growth factors) within the model, thereby enhancing the physiological realism and stability of vascular models. Furthermore, shear stress significantly influences the biological behavior of cells; simulating and adjusting shear stress can better mimic the biological environment and study its biological effects [16]. Flow rate is also crucial for biological models; appropriate flow rates can affect cell distribution, growth rates, and interactions between cells [129]. Therefore, when designing and operating organ chips, considering the relevance of flow rate to the physiological aspects of the studied biological model is a key factor in ensuring the biological significance and repeatability of experimental results. In summary, understanding the impact of fluid flow and shear stress on vascular models, and appropriately controlling flow rates, is essential for enhancing the biological relevance and physiological fidelity of the models. Overcoming these challenges requires deep collaboration and innovation across the fields of engineering, biology, and materials science. Further advancements in high-precision fluid control technology, biomaterials engineering, and novel chip designs will help enhance the complexity and physiological fidelity of vascular models. The growth factors guide the formation of new blood vessels by activating signaling pathways [40,100]. When designing vascular models, leveraging factors such as the extracellular matrix (ECM) and growth factors, especially in 3D models, offers significant advantages. Firstly, the ECM in a 3D space provides a more complex and physiologically realistic support structure, mimicking the three-dimensional structure and microenvironment of real vascular tissues. This intricate structure supports cell growth, differentiation, and functional expression, better reflecting the realities of tissue engineering and biological research compared to 2D models. Secondly, growth factors like vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) exhibit more precise release and gradient control in a 3D environment, mimicking dynamic stimuli encountered by cells in vivo, thereby promoting proliferation and vascular formation of endothelial cells [129]. Therefore, integrating ECM and growth factors to construct 3D vascular models not only enhances their biological relevance and physiological fidelity but also provides a more accurate and reliable experimental platform for studying vascular-related disease mechanisms and drug screening. However, the in vitro model suffers from poor homogeneity and is susceptible to factors such as cell source, cell type, and cell state.