Page 96 - Physico-Chemical Niche Conditions for Bone Cells

PFF affects pre-osteoblast behavior
RESULTS
Immediate impact of PFF (seconds)
Displacement of a live cell treated by PFF
Before PFF treatment, the side view of the live cell was oval-shaped (red line, Fig. 2A). During PFF treatment, the cell moved up and down. At the 1st sec PFF (12 sec in Fig. 2A), the apex height of the cell was decreased (white line, Fig. 2A). At the 2nd sec PFF (13 sec in the video; Supplemental Video S1; https://figshare.com/s/10665c52af1d50f443a7; DOI: 10.6084/m9.figshare.14386730), the apex height of the cell went back to normal (white line, Fig. 2A). At the 3rd and 4th sec PFF (13 and 14 sec in Fig. 2A), the apex height of the cell was decreased again (white line, Fig. 2A). At the 5th sec PFF (16 sec in Fig. 2A), the apex height of the cell was increased to normal height (white line, Fig. 2A). Cell CoM vertical displacement (y-axis) of the PFF-treated cell occurred within 27 sec (Fig. 2B). Before PFF treatment, the displacement of the cell ranged from 0-0.1 μm (0-11 sec, Fig. 2B). PFF treatment changed the range of displacement of the live cell to 0-0.3 μm (12-27 sec, Fig. 2B).
Finite element modeling
We performed finite element (FE) modeling of fluid dynamics inside a parallelplate flow chamber containing an adherent pre-osteoblast subjected to PFF during 5 sec to assess the dynamics of fluid velocity, fluid pressure, and fluid shear stress over time on the cell. The fluid velocity distribution on the pre-osteoblast cell membrane due to PFF was non-uniform and changed over time (Fig. 2C). The highest average fluid velocity magnitude (5.27 mm/s) was detected at 0.25 sec and every sec thereafter, while the lowest average fluid velocity magnitude (0 mm/s) was observed at 0.75 sec and every sec thereafter (Fig. 2D). The average fluid velocity was oscillating between 0 and 5.27 mm/s at each pulse (1 sec). At the apex of the pre-osteoblast, the fluid velocity was oscillating between 0 and 9.7 mm/s at each pulse (Fig. 2E). The magnitude of fluid velocity on the apex of the pre-osteoblast was ~2-fold higher than the average fluid velocity on the pre-osteoblast at all time-points measured (Fig. 2E). The fluid pressure distribution on a pre-osteoblast cell membrane due to PFF was uniform and changed over time (Fig. 2F). Moreover, the fluctuation in fluid pressure on the pre-osteoblast over time showed that the fluid pressure was highest (212 Pa) at 0.25 sec and every sec thereafter, while the lowest fluid pressure magnitude (0 Pa) was observed at 0.75 sec and every sec thereafter (Fig. 2G). The average fluid pressure on the cell was oscillating between 0 and 212 Pa at each pulse (1 sec; Fig. 2G). The fluid pressure on the apex of the cell was
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