*3.3. Flow Patterns Monitoring with Bionic Microfluidic Devices*

After being exposed to a 25, 50, 75, and 100 Pa shear stress environment for 10 min, blood samples were collected for the bionic microfluidic device test. The initial flow rate of blood sample injected into microfluidic devices was maintained as 0.12 mL/min by a micropump. As shown in Figure 4, compared to the morphological characteristics of red blood cells (RBCs) exposed to 25 and 50 Pa shear stress force, more poikilocytes (characterized by sphericity), swelling, and multiple spines were found in the 75 and 100 Pa groups. The mean migration rate of erythrocytes at the posterior region of stenosis in the bionic microfluidic channel, which were subjected to 0, 25, 50, 75, and 100 Pa for 10 min, were 467.55 ± 74.16, 444.39 ± 41.82, 354.43 ± 46.93, 250.91 ± 34.67, and 152.87 ± 27.33 μm/s, respectively. With the increase of shear stress force applied, the migration rate of damaged erythrocyte in the bionic microchannel declined significantly. However, the aggregation of RBCs rose notably with the increase to an exposed shear stress environment, which was synchronous with the degree of erythrocyte damage assessed previously. Moreover, thrombus was captured in the microchannel of the 75 and 100 Pa groups. The migration of thrombus and surrounding flow rate of 75 and 100 Pa groups

were slower than the other two groups. These results indicate that slow flow patterns can also lead to thrombus deposition and adhesion in arterioles.

**Figure 3.** The changes of plasma lactic dehydrogenase (LDH) concentration under different shear stress and exposure times. (**a**) With the increase of shear stress, the concentration of plasma LDH showed an increase trend, especially above 50 Pa, the LDH release presented a rapid raise; (**b**) With the extension of the exposure time, the concentration of plasma LDH in 25 and 50 Pa shear stress environments rose slowly, but in an 100 Pa environment, showed a rapid increase.

**Figure 4.** Migration rate and aggregation of damaged erythrocyte in microfluidic devices. All the blood samples were subjected to each shear stress environment for 10 min. The initial flow rate injected into devices was 0.12 mL/min. With the increase of shear stress, the blood cell migration rate declined, but the aggregation increased. Yellow arrow: erythrocyte; Blue arrow: adhesion thrombus; Red arrow: moving thrombus (scale bar: 20 μm).
