HRMECs cultured on individual glass plates were exposed to seven levels of prolonged shear stress (0, 1.5, 6, 15, 30, 60, or 100 dyne/cm
2) for 24 hours.
Figure 2A shows the magnitude-dependent effects of flow on the morphology of the cultured HRMECs. Under the static (0 dyne/cm
2) control condition, the cells of a confluent monolayer appeared to be polygonal and randomly disposed. In contrast, under flow conditions, the cells gradually elongated and aligned parallel to the direction of flow as the shear stress increased. Notably, the cells remained viable without desquamation even at 100 dyne/cm
2. A quantitative analysis of the aspect ratio as a measure of cellular elongation is shown in
Figure 2B. The aspect ratio significantly (
P < 0.01) increased up until 15 dyne/cm
2, whereas the aspect ratios from 30 to 100 dyne/cm
2 did not differ significantly from that observed at 15 dyne/cm
2. The angle difference between the major axis of each cell and the flow direction is shown in
Figure 2C. Static cells appeared to be oriented randomly, with a mean angle difference of 45.4°, whereas cells exposed to 6 dyne/cm
2 or more were significantly (
P < 0.01) aligned, with a mean angle difference of 23.5° or less. Likewise,
Figure 3A shows the time-dependent flow effects on the morphology of the HRMECs. When the cells were exposed to 60 dyne/cm
2 for 0, 1, 3, 6, 12, and 24 hours, the aspect ratio (
Fig. 3B) and the angle difference (
Fig. 3C) changed significantly (
P < 0.01) after 6 hours of exposure to flow.