## 3 Results and Discussion
### Blood Flows Controlled with Peristaltic Pump  
To supply the blood with a peristaltic flow pattern, the syringe pump was replaced by a peristaltic pump. Quantitative information on blood flow controlled by the peristaltic pump was not specified. Based on a flow stabilizer [58], unstable blood flow was stabilized with an air compliance effect. By adjusting the air cavity secured inside the flow stabilizer, variations in the four properties of blood flow (i.e., \(P_{r}\) [\(I_{c}\)], \(\tau_{r}\), \(w_{P}\), and \(w_{\tau}\)) were evaluated. Thereafter, by supplying aggregation-enhanced blood into a microfluidic channel, the four properties were obtained over time. Figure 8A(a) showed a schematic diagram of _the_ in vitro fluidic system. The experimental setup was composed of a microfluidic device integrated with a flow stabilizer, a  
Figure 7: Contribution of hematocrit to four parameters (i.e., \(P_{r}\), \(\tau_{r}\), \(w_{P}\), and \(w_{\tau}\)) under sinusoidal blood flow. Glycerin solution (20%) as the reference fluid was supplied at the flow rate of 0.5 mL/h. Hematocrit of blood was adjusted to Hct = 0, 20%, 30%, 40%, and 50% by adding normal RBCs into plasma. After a disposable syringe filled with blood was installed horizontally, blood as test fluid was delivered at the flow rate of \(Q_{l}\) = 0.9 + 0.7 sin (2 \(\times\)\(\pi\)\(\times\)\(t\)/360) mL/h. **(A)** Temporal variations of \(\beta\) and \(l_{b}\) with respect to Hct. (a) Temporal variations of \(\beta\) with respect to Hct. (b) Temporal variations of \(l_{b}\) with respect to Hct. Inset showed image of a driving syringe filled with blood (Hct = 30%, and 50%) captured at \(t\) = 0 and \(t\) = 30 min. **(B)** Variations of four factors (\(P_{rs}\) [\(I_{c}\)], \(\tau_{r}\), \(w_{P}\), and \(w_{\tau}\)) with respect to Hct and \(\beta\). (a) Variations of \(P_{r}\) (\(I_{c}\)) with respect to Hct and \(\beta\). (b) Variation of \(\tau_{r}\) with respect to Hct and \(\beta\). (c) Temporal variations of \(w_{P}\) with respect to Hct. (d) Temporal variations of \(w_{\tau}\) with respect to Hct. peristaltic pump (Techpre pump, Jeniwell, Seoul, Korea) for blood, and a syringe pump for glycerin solution (20%). The microfluidic device consisted of two inlets (a, b), two outlets (a, b), two guide channels for two fluids, a coflowing channel, and a large channel for connecting the flow stabilizer. To stabilize unstable pulsatile blood flow by means of the air compliance effect, the air cavity inside the fluidic stabilizer was secured by adjusting the tubing length (\(L\)) (\(L\) = 20, 100, 200, and 300 mm), and closing one side end with a drawing pin. A tube (\(\sim\)5 mL) was filled with blood (i.e., normal RBCs in plasma, Hct = 50%, and blood volume = 4 mL). A peristaltic pump set to \(\Omega\) = 0.5 rpm. The syringe pump set to 0.5 mL/h to supply the glycerin solution (20%). Figure 8A(b) showed a microscopic image of microfluidic channels filled with the blood as well as glycerin solution (20%). As blood flow had a higher pressure than the glycerin solution, blood moved from the inlet (a) to the outlet (a). In addition, blood flowed from the connecting channel to the upper right channel (i.e., the coflowing channel). The glycerin solution flowed from the right lower channel to the right upper channel. Blood and glycerin solutions met in the right upper channel (i.e., coflowing channel). The interface (\(\beta\)) was determined by the dynamic flow of the two fluids. Using the present method, it was possible to monitor blood flow in the coflowing channel by means of four blood flow properties (i.e., \(P_{r}\), \(\tau_{r}\), \(w_{P}\), and \(w_{\tau}\)). As shown in Figure 8B, the contributions of the flow stabilizer to flow stabilization were quantified by adjusting the length of the tubing size (\(L\)). Figure 8B(a) showed the temporal variations of \(\beta\) with respect to \(L\). According to a previous study [58], an air cavity secured inside a disposable syringe caused a substantial increase in air compliance.