## 2 Materials and Methods
### Structural Construction
#### 2.1.1 Three-Dimensional Modeling Design
In this experiment, the simulation of incompressible flow with low velocity flow is used, and the liquid velocity is used as the main variable, so the type of pressure-based solver is selected, and the momentum equations are solved sequentially to calculate the velocity field, and the mass conservation equations are solved to calculate the pressure field until the convergence condition is reached to get a stable solution of the flow field. Set the \(Y\)-axis gravitational acceleration to \(-9.81\) m/s\({}^{2}\). Additionally, since this experiment requires modeling heat transfer, the energy equation is activated. The flow regime is determined via the Reynolds number, expressed as shown in Equation (1):  
Figure 1: CAD model of square pore unit cell scaffold and fluid domain. Figure 2: Grid model. \[\mathrm{Re}=\frac{\rho\
u L}{\mu}, \tag{1}\]  
Here, Re represents the Reynolds number; \(\rho\) is the fluid density in kg\(\cdot\)m\({}^{-3}\); \(\
u\) is the characteristic flow velocity in m\(\cdot\)s\({}^{-1}\); \(L\) is the characteristic length in m; and \(\mu\) is the dynamic viscosity of the fluid in Pa\(\cdot\)s.  
After pre-calculation, the Reynolds number of the flow model is much less than the critical value of 2000, and the flow is laminar, so the laminar model is selected in the viscosity option. DMEM (Dulbecco's Modified Eagle Medium) was selected as the simulation liquid material, and the physical properties of DMEM were set as density 1036 kg/m\({}^{3}\), specific heat 4182 J/kg\(\cdot\)k, thermal conductivity 0.6 w/m\(\cdot\)k, and viscosity 0.00145 kg/m\(\cdot\)s. When regulating the temperature, the change in physical properties with temperature needs to be considered, and the physical properties need to be set to piecewise-linear form, the solid material of the stent is selected as TC4 (Ti-6 Al-4V), and the physical properties are set to a density of 4430 kg/m\({}^{3}\), a specific heat of 613 J/kg\(\cdot\)K, and a thermal conductivity of 6.93 W/m\(\cdot\)K. The surrounding fluid surface is set to symmetric condition. The fluid inlet is set as a velocity inlet, different inlet velocities are set according to the demand of simulation and analysis, the temperature is set as 310 K, and the outlet is set as a 0 Pa pressure outlet. The solid and fluid interfaces were coupled to each other to simulate thermal mass exchange. Considering that the flow model is a low Reynolds number laminar flow, but the flow region is relatively complex, in order to meet the accuracy requirements and time and cost considerations, the coupled solver (Coupled) is selected in Fluent, the gradient term is selected based on the cell-based least-squares method, the discretization of the pressure term is selected in the PRESure STaggering Option (PRESTO!) format, and a second-order upwind scheme is used for the momentum and energy terms. The relaxation factor (ranging from 0 to 1) in the solution control can adjust the preference of convergence and convergence speed when solving, decreasing the relaxation factor makes the convergence speed slower while the convergence improves; increasing the relaxation factor will speed up the convergence speed and decrease the convergence. The relaxation factor should be adjusted according to the simulation when simulating. The convergence criterion of the residuals is set to 0.00001 to ensure the accuracy of the results, and the calculations are run after mixing initialization. 3. Post-Processing
* Mesh Irrelevance Study  
Grids with different cell counts were generated for the square-pore unit cell-type scaffold model, and simulations were performed under conditions of a fluid inlet velocity of 1 mm/s and a temperature of 310 K. Computations diverged when the grid cell count was below 800,000. Due to workstation hardware limitations, the maximum grid cell count was 7,590,000 cells. Four groups of valid data were extracted, with grid sizes of 996,728, 2,219,115, 3,721,514, and 7,591,866 cells.