Osteoblast recruitment in the flow direction and motility under shear are increased with ROCK interference.

<p>(a) Osteoblasts with ROCK-shRNA (ROCK-sh) under FF25 showed significantly greater number of cells migrating with the flow direction. (b) Even after the initial period, the speeds of ROCK-silenced cells were greater for both static and sheared conditions (e.g., 60 min). (c) The displacement of ROCK-shRNA FF25 group assessed after 120 min was significantly greater compared with other conditions. (d) The ROCK-shRNA static group was less confined in migration path. (e) The ROCK-shRNA cells paused significantly less during the migration. (f) The RMS displacement shows that the collective migration of the ROCK-shRNA FF25 group was continued throughout the measurement time resulting in greater RMS displacement at 120 min. The dashed vertical line marks 30 min after the flow onset. *: comparison with vector control static. ‡: comparison with vector control FF25. +: comparison with ROCK-shRNA static. Single, double, and triple symbols represent p < 0.05, 0.01, and 0.001, respectively.</p

The displacement length and arrest coefficient of osteoblast migration show fluid shear sensitivity but only for a short period after the flow onset.

<p>Data were presented for the short-term (from 0 to 30 min) and long-term (the entire tracking from 0 to 120 min) durations. (a) The short-term displacement increased with shear. FF25 migrated significantly further than the static control. These differences were not observed in the long-term data. (b) There was no significant difference in the confinement ratio (directness of the migration path) with respect to shear stress. The ratio generally decreased for all test conditions as time increased, indicating reduced path efficiency with time. (c) Flow groups had significantly smaller arrest coefficients (less time paused) compared with the static control in the short-term data, which was not observed in the long-term result. *, **, and ***: p < 0.05, 0.01, and 0.001 compared with static control; ##: p < 0.01 with FF2; ψ: p < 0.05 with FF15.</p

Motility coefficient obtained as a slope of the RMS displacement vs. t^1/2 plot.

<p>Motility coefficient obtained as a slope of the RMS displacement vs. t^1/2 plot.</p

Fluid shear effects on osteoblastic cell migration could be detected.

<p>MC3T3-E1 osteoblasts had a trend of migrating with the flow direction with increasing shear and spent less time migrating against the flow, especially under high shear. (a) Individual cell raw migration tracks. Flow was given from left to right for fluid flow (FF) cases. FF2, FF15, and FF25 denote fluid shear stress of 2, 15, and 25 dyne cm^-2, respectively. (b) Compass plots connecting starting and ending positions. (c) Cell migration is considered to be with the direction of flow if the migration angle in the compass plot is within ± π/8 of the flow direction. (d) Cells showed an increasing trend of migrating with the flow with increasing shear. The percent of cells migrating against the flow did not have a clear trend. (e) The cells under higher shear (FF15, FF25) tended to spend more time migrating with the flow. The FF25 group spent the least time migrating against the flow (#: p < 0.05 compared with FF2).</p