# Research Progress in the Construction and Application of In Vitro Vascular Models
## 2 Construction of In Vitro Vascular Models
### Construction of In Vitro Vascular Model Based on Non-Microfluidics-Based Methods
#### 2.2.2 Construction of Vascular Model In Vitro by 3D Bioprinting
On the other hand, light-assisted bioprinting uses laser pulse energy to deposit cell-laden biomaterials on the substrate, which can cross-link and solidify the biological materials without requiring nozzles [94]. This method can print bioinks with higher viscosity and also has the advantages of high cell viability, high resolution, and high printing speed. However, it needs to be operated in a sterile environment, which makes it complicated to operate. Additionally, this method requires the use of photosensitive bioink, which results in high cost [48]. Therefore, this printing method has not been widely used. In summary, although inkjet and light-assisted bioprinting also have many advantages, the strict requirements for cell density and low cost make extrusion bioprinting the most commonly used bioprinting technology for in vitro printing of vascular structures. In addition to technical properties, bioprinting can also use one or more materials simultaneously [97]. Various hydrogel materials such as alginate, collagen, hyaluronic acid, gelatin, and poly(ethylene glycol) (PEG) can be used as bioinks due to their biocompatibility and high viscosity [98]. However, these biomaterials cannot be used alone for bioprinting hollow microchannels because of their low mechanical strength. Biomaterials with low mechanical strength will not be able to support the weight of the hollow microchannels, leading to the collapse of the microchannels. For instance, [PERSON] et al. [99] designed a cell-responsive bioink using three biological materials: gelatin methacryloyl, sodium alginate, and 4-arm poly(ethylene glycol)-tetra-acrylate. The alginate component is first cross-linked with calcium ions, and then the photo-cross-linking of gelatin methacryloyl and 4-arm poly(ethylene glycol)-tetra-acrylate can further fix the morphology of the microchannel. The bioink has good mechanical strength and biological properties, which are conducive to constructing a complex 3D perfusable vascular network and promoting the proliferation and expansion of encapsulated cells. The use of 3D bioprinting technology can construct biologically relevant, perfusable, and highly organized 3D vascular models in vitro, which are challenging to achieve using traditional microfabrication techniques. Therefore, the emergence of advanced 3D bioprinting technology and bioink formulations may represent a significant milestone in the construction of large-scale vascularized tissues. Bioprinting and pre-manufactured microchannels followed by endothelial cell seeding are two distinct methods for constructing vascular models. bioprinting utilizes layer-by-layer deposition of biomaterials and various cell types to precisely control the shape, size, and complex structure of blood vessels [89]. In contrast, the method of pre-manufactured microchannels involves creating predefined microchannel structures and then seeding cells on their inner surfaces, typically achieved through injection or coating of cell suspensions, ensuring cell attachment to form single-layer or multi-layer cell sheets [19]. Bioprinting enables more precise spatial control and integrated construction of multiple cell types (such as endothelial cells, smooth muscle cells, and pericytes), allowing for the construction of complex vascular network structures including hierarchical branching and the precise arrangement of different cell types. Bioprinting offers significant advantages in building complex tissue models and personalized medicine but it often comes with higher costs and risks of compromising cell viability [90]. In contrast, the method of pre-manufactured microchannels followed by endothelial cell seeding is limited by the precision and complexity of microchannel manufacturing technology, typically suited for simple single-layer or basic channel structures, suitable for constructing vascular models with simpler structures and for functional assessments [100]. This method may be more cost-effective and applicable in certain basic research and specific application scenarios.