Figure 1.

In vitro MSC expansion model and experimental design. (a) MSCs at passage 6 (P6) were serially passaged until P60. Experimental groups were subjected to twice-daily Low Intensity Vibration (LIV) regimen (0.7 g, 90 Hz, 20 minutes) outside of the incubator. While control MSCs were taken out of the incubator for 20 minutes twice daily, they were not vibrated. Each day, flasks were observed for confluence and when either one of the groups reached 70% confluence (non-contact), both groups were trypsinized, counted and re-plated at the density of 1000 cell/cm². This protocol was repeated until passage 60 (P60). (b) Data collected between P12 and P15 were designated as early passage (EP) and data collected P57 and P60 were designated as late passage (LP). All assays were performed 24 h after plating with no LIV applied within the 24 h period. EP and LP samples were compared to P6 samples in separate, independent experiments with the exception of immunostaining where samples were fixed at different times but were stained and analyzed together.