## 3 Results
### Flow Profile  
Pump system:  
The accesses of the upper and lower channels were standardized with luers for easy pipetting and possible adaptation to most of the pump systems. Luers were integrated on each side of the channels, resulting in the possibility to perfuse both channels independently (in this study, only the channel receiving cells was perfused). Inlets and outlets were placed in line with the perfused channel to avoid any flow disturbance [25]. The Ibidi pump system was chosen to drive a constant flow unidirectionally (oscillating flow is considered more suitable for vessel defects, and pulsatile flow was shown to be responsible for alterations in the BMEC phenotype [10]). This system combines the advantages of a syringe pump (bubble trap, visual rapid control of the flow rate due to the graduated syringes), with the possibility to recirculate the flow with reduced dead volumes. We can note that a brief interruption in flow occurs when the syringes switch due to the pinch valve activation. This unavoidable phenomenon creates a very slight pulse that can be neglected in comparison with the long phases of constant flow. The software precisely controls the pressure and records it per minute in a file. The Ibidi pump system provides a wide range of flow rates from 0.09 to 52.5 mL-min\({}^{-1}\), thanks to the different tubing thicknesses available. One pump can drive simultaneously until four fluidic units with independent flow parameters, and one fluidic unit can connect up to three channels in series. Consequently, we can use up to 12 channels under flow simultaneously. Fluidic setups for devices in well plate format and microscope slide format are shown in Figure 2a,b. For visual monitoring \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Effective Culture Volumes and Times:**} \\ \hline \multirow{2}{*}{**Material for Culture**} & \multirow{2}{*}{**Cell Seeding Surface**} & \multirow{2}{*}{**Volume**} & \multirow{2}{*}{**Medium Height**} & **Interval between Two** \\  & & & & **Medium Changes** \\  & **cm\({}^{2}\)** & & & **Hours** \\ \hline T75 Flask & 75 & 15 * & 0.2 & 96 \\ T25 Flask & 25 & 5 * & 0.2 & 96 \\ Barrier device with \(h=0.6\) mm & 3.26 & 0.196 & 0.06 & 29 \\ Barrier device with \(h=0.5\) mm & 3.26 & 0.163 & 0.05 & 24 \\ Barrier device with \(h=0.3\) mm & 3.26 & 0.098 & 0.03 & 14 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of effective culture volumes and times between flasks and our home-made device (including further proposed heights of the upper channel (\(h\))). Medium heights in flasks were calculated by dividing the volume by the cell surface, while medium heights in devices corresponded to the height of the upper channel as it was filled with medium. Interval between medium change in flask corresponds to 50 \(\mu\)L/cm\({}^{2}\)/day. * Usual volumes recommended by the supplier. (Wells and Transwell® cannot be taken into consideration because of the bias of the meniscus effect). of cells, a tubing of 50 cm length allows to put the device on the microscope stage without interrupting the shear stress (the fluidic unit stay in the incubator). In addition, it is possible to integrate this system into a live cell culture microscopy platform for real-time imaging. Flow rate:  
In our device, the flow can be applied to both channels. Here, we present our calculations to set up the upper channel, as it receives the cells (that recover the porous membrane at the bottom of the channel). Depending on the flow rate (\(Q\)) configured on the pump system, cells are submitted to a proportional shear stress (\(\tau\)). Shear stress is defined by the product of the medium viscosity (\(\mu\) = 0.72 \(\times\) 10\({}^{-3}\) N\(\cdot\)s\(\cdot\)m\({}^{-2}\) for culture medium at 37 \({}^{\circ}\)C with 10% of serum) and the shear rate (\(\partial v/\partial y\), which corresponds to the change in flow velocity through the channel) [23; 26].