# Research Progress in the Construction and Application of In Vitro Vascular Models
## 3 Application
### Blood Vessels Associated with Cancer  
Cancer research utilizing in vitro vascular models is another important area of study. The blood vessels surrounding tumors play a critical role in tumor growth by supplying oxygen and nutrients and also contribute to metastasis [11]. As a result, various in vitro vascular models have been developed to investigate the impact of vasculature on cancer. In one study, [PERSON] et al. [113] created a three-dimensional microfluidic cell array composed of three PDMS layers. This model maintained nutrient supply and waste metabolism of the encapsulated cells through continuous perfusion in the microchannel. The research demonstrated that this model sustained high cell viability for up to two weeks. It was successfully employed to establish human breast cancer and lung cancer models using the respective cancer cells, enabling high-throughput screening of potential anti-cancer drugs. In another study, [PERSON] et al. [114] utilized a hydroxyethyl cellulose-based bioink mixed with sodium alginate to develop a cervical cancer model via 3D bioprinting technology using HeLa cells. Cell viability was minimally affected during the process, and after one week of cultivation, the cell count increased significantly. The research indicated that low concentrations of sodium alginate in the bioink had little impact on cell viability. However, higher concentrations of sodium alginate (5%) and longer printing times have a negative effect on initial cell viability. The researchers used this model to evaluate the effectiveness of paclitaxel and observed its cytotoxic effect on the hydrogel. This model can be utilized for screening other anti-cancer drugs. In addition to screening anti-cancer drugs, cancer-related models can also be utilized to investigate the mechanism of angiogenesis at cancer sites and the phenomenon of cancer metastasis. [PERSON] et al. [115] (Figure 5) replicated the budding process of endothelial cells in the tumor environment using a tumor chip, and by day 5, the model formed a vascular-like structure. This result indicates that the chip successfully simulated the angiogenesis process in the rectal cancer microenvironment. Compared to traditional in vitro models, this platform is closer to the physiological environment and shows promise as a drug screening platform. However, the lack of pericyte support in this model can hinder the stability of blood vessels. Additionally, this model lacks important features of natural blood vessels, such as fluid flow. [PERSON] et al. [116] developed a triangular multi-cavity tumor chip platform. Research shows that the chip can ensure dynamic culture and maintain high vitality in human breast cancer cells for at least one week. Starting on day 8, the hydrogel began to gradually degrade, and by day 15, most of the hydrogel had degraded. Furthermore, research indicates that the large-pore hydrogel--formed by adjusting the proportion of hydrogel--promotes cell growth, providing a good platform for constructing in vitro tumor models, investigating the mechanism of tumor metastasis, and screening antitumor metastasis drugs. [PERSON] et al. [117] developed an in vitro tumor vessel model using the template method. Tumor cells had a survival rate of more than 90% in the hydrogel and maintained proliferative activity during the three-day experiment. By evaluating shear-induced endothelial morphological changes, it was found that endothelial cells maintained their integrity under the physiological shear-stress environment. The study also investigated the impact of shear stress on microvessels and the paracrine signaling of breast cancer cells. However, current in vitro cancer models have limitations. For instance, three or more cell cultures in the blood-brain barrier model make it difficult to observe cell growth and take a long time to measure transmembrane resistance. Furthermore, current cancer models lack the immune system, which plays a crucial role in the immune clearance of tumor cells.