## 3 Results and Discussions  
### Circular Microchamber  
It was possible to analyse the distribution of the fluid within the microchannel using the streamline plot. It can be observed that the fluid spread throughout the cultivation chamber assumes a different velocity magnitude depending on the applied flow rate atthe inlet of the device. The highest velocity value occurred in the centre of the chamber, whereas the velocity tended to decrease towards the walls of the device due to the non-slip boundary condition applied to the walls of the device (Figure 5a-c).  
Before modelling, the wall shear stress values for flow rates of 2, 6, 10 \(\mu\)L/min were calculated using Equation (4) (5 \(\times\) 10\({}^{-3}\), 1.5 \(\times\) 10\({}^{-2}\), 2.5 \(\times\) 10\({}^{-2}\) Pa, respectively). The results obtained from the simulations show that the values of wall shear stress are very low in the circular microchamber (Figure 5d-f). Consequently, both the velocity and the wall shear stress profiles, which are related to the above three flow rates, were plotted versus the width of the circular chamber (1 mm) (Figure 5g,h).  
Figure 5: Simulated shear stress and velocity magnitude along the red line are plotted versus the width of the circular microchamber using three different flow rates of 2, 6 and 10 \(\mu\)L/min. (**a–c**) The fluid flow; (**d–f**) wall shear stress simulations within the circular microchamber with a microchannel height of 200 \(\upmu\)m and flow rates of 2, 6 and 10 \(\mu\)L/min; (**g**) the velocity profiles; (**h**) wall shear stress profiles at h = 0 \(\upmu\)m (solid lines), which is at the bottom of the microchamber, and h = 100 \(\upmu\)m (dotted lines), which is the shear stress at the middle of the microchamber; (**i**) generated mesh density study of the circular microchamber. The small dots in Figure 5a–c are the velocity direction arrows.  
As mentioned above, the ratio between the height and width of the microchannel determines the velocity and wall shear stress profiles within the microchannels. In this case, as the aspect ratio of the microchannel is greater than 1 (cultivation chamber = 1 mm >> h = 200 \(\upmu\)m), the velocity profile within the microchamber indicates a parabolic shape, with a maximum velocity occurring in the centre of the chamber and a minimum velocity at the walls due to the non-slip condition. Figure 5h shows that when moving from the bottom (h = 0 \(\upmu\)m, solid lines) to the centre or middle (h = 100 \(\upmu\)m, dotted lines) of the microchamber, the wall shear stress increases at the wall and decreases in the middle (Equation (3)). Overall, this circular microchamber geometry showed low values of velocities and wall shear stress, thus making it suitable for cell culture studies which require low values of these parameters. Importantly, the low shear stress values negatively affect focal adhesion formation as well as cell proliferation and migration [48; 53; 54].  
Moreover, the velocity profile assumes different values in various parts of the microchannel (Figure 5a-c), and this phenomenon can affect the uniformity of the cells' arrangement in cell culture studies [22]. A similar geometry was studied to evaluate the fluid flow behaviour and the velocity profile distribution within the channel using a single value of velocity [53]. However, in this study, different flow rates were used in order to evaluate their effects on both shear stress and velocity profile distribution within the channel. Figure 5i demonstrating the mesh study of the circular microchamber shows a total of 248,087 elements, which is adequate to guarantee a grid-independent solution.