## 2 Materials and Methods  
Two arterial phantoms were used in this study. First, an idealized 1:1 scale compliant phantom of the basilar artery with posterior cerebral branches was designed with an aneurysm at the bifurcation (Figure 1a). Another 1:1 scale model of the basilar artery with a sidewall aneurysm was designed (Figure 1b). The phantoms were manufactured from Silicone Sylgard-184 (Dow Corning Inc. Midland, MI, USA) at room temperature (23 \({}^{\circ}\)C) (Figure 1c). The lost core casting method developed by [PERSON] et al. [22] was used for phantoms manufacture; the details of the moulding process can be found in their study. It was reported that the Sylgard-184 has a Young's modulus of 1.32 MPa if it is cured at room temperature [23; 24]; thus, it was not measured in this study. In total, 7 experiments were conducted and 4 implants were tested. Cases 2 and 3 (generations 2 and 3) were eCLIPs coil assisting implants commercially available on the market. Case 4 (generation 4) was a revision developed with higher metal coverage. A schematic view of an eCLIPs implant in bifurcation configuration is shown in Figure 2a. Since the PED implant is the prototypical FD, its measure of flow diversion was used as a reference to compare the eCLIPs' results. The PED was implanted in both bifurcation (Case 5) (Figure 2b) and sidewall (Case 7) configurations (Figure 2c). Cases 1 and 6 were the silicone models without any implant and served as baselines to assess the flow diversion effect. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Series** & **Implant Figure** & \
\begin{tabular}{c} **Metal** \\ **Coverage** \\ **(Density)** \\ \end{tabular} &
\begin{tabular}{c} **Common** \\ **Geometry** \\ **Implanted** \\ \end{tabular} & **Purpose of Use** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Illustration and general characteristics of the three versions of eCLIPs and Pipeline studied using particle image velocimetry (PIV) analysis; the Pipeline device image was adapted from [PERSON] et al. [21]. A fluid circuit was developed to run the flow through the phantoms (Figure 3). A solution of 47.38% water, 36.94% glycerine, and 15.68% sodium iodide was used as a blood analogue [25]. The circuit consisted of a steady pump, magnetic-inductive flowmeter (SM 4000, IFM Inc., Daimlerring, Germany), phantom box, reservoir, and header tank. The header tank was used to mimic the impedance of the smaller arteries and capillaries. To eliminate the vibration in the fluid line and aneurysm due to the pump propulsion, the fluid was pumped to a reservoir (Figure 3) and gravity-fed to the model. A weir was designed in the reservoir to keep the fluid level constant. To eliminate optical distortion during the PIV experimentation, the working fluid should have the same refractive index as the silicone phantoms. The phantom box was also filled with the same working fluid to mimic the surrounding tissue. This solution matched the refractive index of the silicone Sylgar-184 (\(n=1.414\)), which was verified by placing a checkerboard behind the phantom and capturing images to check for distortion of the grids. The solution had dynamic viscosity of 4.31 cP, which is in the range of human blood viscosity [25]. The volumetric flow rate in the basilar artery can reach up to 300 mL/min at peak systole [17; 26]. Since it was expected to see the highest velocity and blood protrusion into the aneurysm at peak systole, all the experiments were conducted at a 300 mL/min steady flow. Since there are no published data on the shear rate threshold for successful flow diversion and thrombosis formation in a bifurcation aneurysm, the current study only mapped the velocity field in the aneurysm sac and discussed the flow diversion based on the velocity reduction. Figure 1: (**a**) Bifurcation aneurysm model drawing, (**b**) sidewall model drawing, and (**c**) sample image of the manufactured silicone model; length units are in mm. Planar PIV was used to capture the fluid dynamics within the aneurysm dome.