## 3 Results and Discussion
### Inlet and Outlet Effects  
It is highly desired to have a flat velocity profile along the whole CC, as was shown in Figure 6b, since it allows for maintaining homogeneous conditions of cell culture across the chamber in the same cross-section, allowing to grow cells in the same microenvironment. Inlets and outlets disturb velocity profiles, but the small height of the channel promotes the development of a plug-flow-like profile in a short distance from inlets/outlets. It is interesting to distinguish how long the development regions are. As the flow enters a duct, the velocity profile begins to develop along its length, ultimately reaching the fully developed velocity profile. Almost all the analyses available in the literature neglected the inlet/outlet effects, but the relatively short length of the CC may mean that such disturbances may affect the culture microenvironment and consequently influence the results of tests performed on a chip. In Figure 7, the distributions of magnitudes of the Z-direction velocity gradient, V\({}_{\text{z}}\), the dynamic pressure, P\({}_{\text{D}}\), and the shear stress, \(\tau\), at the bottom surface of the CC are presented, where the cells adhere. Since shear stress, shear time, and pressure changes can severely affect cell viability, phenotype, and function [29, 30], it is interesting to determine the ranges of the variability of these parameters under standard chip operating conditions. The distributions of such parameters in the working area of CC (between two vertical lines) are uniform in the Y direction, and vary only slightly in the X direction (V\({}_{\text{z}}\): 258-290 (1/s), P\({}_{\text{D}}\): 0.4-5.2 (Pa), \(\tau\): 0.258-0.29 (Pa)). Bearing in mind that the flow exerts on cells only for a very short period of time, when gradients in CC are generated, we can definitely say that its influence on cells is negligible in standard operating conditions. In Figure 8, the velocity distributions at the inlet of CC are presented. Velocity vectors that point out from the fluid reservoir indicate that fluid may pour out of the tank, but the surface tension prevents fluid from escaping the grove. Near the inlets, the parabolic velocity profile in the culture chamber with the near-wall flatness was observed. This is caused by the circular shape of the reservoirs and the uneven outflow of liquid from the reservoirs to the chambers. Figure 6: Results of the simulation. Velocity profiles in a culture chamber of the microdevice: (**a**) plot over line C and (**b**) plot over line D.  
Similar observations have been made during experiments and are presented in Figure 9a,b, where we can see dynamic profiles of the dye introduced to the inlets of CC from the reservoirs. In Figure 9b,d, normalized profiles of the dye in a dimensionless coordinate system are presented, obtained from the microscopic photos. The dashed line represents the shape of the reservoir edge. In each CC, the observed dye profile is of the same tongue-like shape, with a near-wall flatness. The discrepancy of the dye contour from the circular shape of the reservoir outlet edge evidenced the flow unevenness in this case. Figure 8: Fluid velocity distributions at the inlet of CC: (**a**) velocity vectors and wrapped-by-vector velocity profile, (**b**) velocity profile and velocity streamlines at the inlet of CC—half view, and (**c**) XZ channel cross-section. Figure 7: Z-direction velocity gradient magnitude, dynamic pressure, and shear stress distributions at the bottom surface of CC. region. As the dye moves deeper into the chamber, the profiles become flat, as can be seen in Figure 9c,d. As we can see from Figure 10, the simulations predict that the discrepancies from the uniform distributions of flow parameters are observed close to the inlets only, and do not affect cell cultures in the CC working zone. The simulated velocity profiles flatten out when the fluid approaches the edge of the chip's workspace (line 6 in Figure 10b,c).