# Research Progress in the Construction and Application of In Vitro Vascular Models
## 3 Application
### Endothelial Dysfunction  
Endothelial dysfunction is associated with the development of thrombosis, atherosclerosis, and inflammatory diseases [109]. The mechanisms underlying thrombosis and atherosclerosis are complex and involve numerous factors. Therefore, in vitro models play a crucial role in predicting disease progression, risk levels, and determining treatment options. [PERSON] et al. [110] constructed an in vitro thrombus model to evaluate the efficacy of antithrombotic drugs. The researchers first inoculated endothelial cells into the microfluidic channel. Studies have shown that endothelial cells assemble into a single layer within 24-48 h under perfusion conditions and begin to function appropriately. Tumor necrosis factor alpha was then used to activate the endothelial cells, causing tube occlusion to form a thrombus model. The researchers used this model to test the effectiveness of hydroxyurea drugs on thrombosis. The study showed that the fluid blockage in the tube improved after adding the drugs. Thus, the thrombus model can be used to evaluate antithrombotic drugs and serve as a screening platform for drug discovery. However, due to the microfabrication technology of the microfluidic chip, the cross-section of the above model is rectangular and does not match the physiological structure of the blood vessel. Therefore, it cannot fully simulate the vascular microenvironment. Nonetheless, the endothelial cells inoculated into the channel can form an approximately cylindrical vascular cavity, making the system more physiological. Additionally, cell-loaded hydrogel constructs composed of growth factors, hydrogels, and cells provide a favorable in vitro environment for studying endothelial dysfunction. Thus, cell-loaded hydrogels with ideal geometry, size, and composition can be developed to bring the model closer to the physiological environment.  
[PERSON] et al. [111] (Figure 4) used collagen gel to co-culture endothelial cells and smooth muscle cells. Studies have shown that co-culture can affect cell gene expression and lead to the production of a variety of adhesion molecules and chemokines. This model provides new insights into the mechanism of interaction between leukocytes and the vessel wall in patients with atherosclerosis.  
Figure 4: Schematic diagram and flow patterns of the vertical-step flow (VSF) channel structure. (**a**) Schematic diagram of the channel. ((**b**), (**top**)) Microphotographs showing experimental flow patterns in the VSF channel (top view). ((**b**), (**bottom**) Side-view schematic diagram of VSF streamlines inferred from top-view microphotographs. Flow separation occurs in the region farthest from the step, forming four distinct flow regions: (**c**) stagnation zone, (**d**) recirculation vortex zone, (**e**)  reattachment flow zone, and (**f**) flow redeveloping into laminar flow region as shown at the bottom of the figure. Reprinted/adapted with permission from Ref. [111]. 2006, Amer Soc Hematology.  
In another study, [PERSON] et al. [112] used fibrin gel to construct an atherosclerosis model. The researchers first inoculated smooth muscle cells into the fibrin gel, and after 14 days, the smooth muscle cells formed a mature network structure. Then, the endothelial cells were inoculated on the surface of the gel, and the two cell types were continuously cultured for 4-6 weeks. The study confirmed that the model had high viability and functional integrity. After 28 days, low-density lipoprotein was used to induce atherosclerosis. The model had good long-term stability and could be used to study atherosclerosis for up to 6 weeks. However, established in vitro models cannot fully simulate human endothelial dysfunction. Additionally, these models still have shortcomings such as poor reproducibility, lack of homogeneity, and inadequate mechanical properties. Therefore, cell-loaded collagen can be combined with microfluidic chips to create more advanced models.