FIG. 3.

MSCs grow in size in culture. Using the median forward scatter (FSC) as a surrogate for cell size, the rare native MSCs present in freshly isolated rat bone marrow (i.e., the CD45⁻/CD73⁺/CD90⁺ gated fraction, representative flow profile in A1) appeared much smaller than the ones expanded in culture under both conditions (A2, A3, p<0.01). After 6–8 weeks in culture monolayer-expanded MSCs (A2) were significantly larger than MSCs expanded in parallel in bioreactor (A3, average FSC data in A4). This was confirmed by direct measurement of cell size following MACSs bioreactor cell separation using an automated cell counter (representative photomicrographs from monolayer and suspension MSCs in B1 and B2, respectively, and summary data in B3). The apparent increase in cell size over time of the mixed cell population present in bioreactors and monolayer conditions is illustrated in (C), p<0.05 or 0.001 as indicated. Scale bar, 100 μm. Color images available online at www.liebertpub.com/tec