# 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
#### 2.2.3 Construction of Vascular Model In Vitro by Laser Degradation or Laser Cavitation Molding  
Laser degradation is a method that selectively degrades or ablates the cell-filled hydrogel using laser energy to form a network structure. Endothelial cells are then arranged and grown within the hydrogel to form a complex three-dimensional vascular network, as shown in Figure 3. This method has high resolution, is easy to use, and is not limited by complex three-dimensional shapes. Additionally, sterility is ensured as this method uses light to create three-dimensional networks [49; 50]. Hyaluronic acid, collagen, PEG, agarose, and other materials can be used to construct three-dimensional networks by laser degradation. This method allows spatiotemporal control of fluid channel formation and fluid flow. However, this thermal ablation process can cause denaturation of proteins in the hydrogel and has some impact on cell compatibility [101]. Moreover, this method requires the use of expensive multi-photon systems for high resolution. For example, [PERSON] et al. [102] successfully constructed an endothelialized glomerular structure in vitro using multiphoton and laser-guided angiogenesis techniques. They first used lithography to create two parallel vessels into which human umbilical vein endothelial cells were seeded. A 10 \(\upmu\)m channel was then created in the hydrogel by laser ablation to connect the pre-formed parallel vessels, resulting in the formation of a glomerular vessel model. Figure 3: Fabrication of vascular networks in hydrogels by laser degradation. Researchers have combined laser degradation technology with image-guided laser control to form highly complex, tortuous, and high-resolution three-dimensional structures in hydrogels. These networks accurately reproduce the structure, size, and density of microvessels in the body and can form endothelial networks together with endothelial cells [103]. This method can accurately simulate the vascular network in vivo by controlling parameters such as the total length of the network, the number of branching points, and the average vessel diameter. Moreover, this image-guidance method relies on the use of virtual masks so that the masks can be easily designed and modified by simple digital operations, which is different from the need to redesign and modify the master using lithography technology. In summary, this method can be used to build capillary-sized vascular networks and replicate the dense and tortuous structures of vascular networks in vivo [103]. Although the above method has many advantages, it can have some impact on the proteins in cells and hydrogels. Therefore, a more ideal pipeline construction method has recently been developed by a research team. [PERSON] et al. [15] proposed a new method to construct a three-dimensional pipeline structure by laser cavitation. The researchers first used a low-energy femtosecond infrared laser pulse to perform non-ablative recombination of collagen hydrogels. The expansion of the cavitation bubbles rearranged the hydrogel structure to create a circular hollow tube with a diameter of 20-60 \(\upmu\)m, which was stable for at least 8 days under physiological conditions. The researchers then inoculated the tube with endothelial cells to create a vascular model. Unlike the laser degradation method, this method can minimize the thermal diffusion volume and mechanical stress on the cells to improve cell viability. This method has no effect on cell viability whether the cells are outside the tube or inside the hydrogel. However, this method is only applicable to collagen hydrogels [50]. In summary, laser-induced cavitation in collagen hydrogels allows the formation of microchannels of any shape and size, which are then filled with endothelial cells to create a simulated vascular network in vivo. This method forms a 3D microvascular tissue model by irradiating collagen hydrogel with a femtosecond laser, making it possible to use a 3D tissue model to study complex tissues such as tumors and neural tissue.