The effect of culture conditions on the adipogenic and osteogenic inductions of mesenchymal stem cells on micropatterned surfaces

Herein we examined an adipogenic or osteogenic induction of rat bone marrow mesenchymal stem cells (MSCs) in the corresponding media and a co-induction in a 1:1 mixed medium. The cell size effect and cell–cell contact effect were employed as two demonstrations to check the similarity or difference of the effects under these two induction ways. We seeded cells on a micropatterned surface with cell-adhesive microislands on poly(ethylene glycol) hydrogels. MSCs were well localized on the microislands separated by the strong and persistent non-fouling background, which enabled the observations of individual cells of varied sizes and numbers. We made statistics of adipogenic and osteogenic differentiations of single MSCs of different sizes (170–5600 μm2) and also of cell clusters of different aggregation numbers (1, 2, 4 and 8 etc.) with small, medium or large cell sizes. Both sole induction and co-induction led to monotonic cell size effects: small cells favored the adipogenic differentiation, and large cells preferred to the osteogenic differentiation. The effects of cell–cell contact were, however, rather complicated: the aggregation among cells was beneficial for both adipogenic and osteogenic differentiations, as revealed from the sole inductions; but under the co-induction culture in the mixed medium, the inherent enhancement of differentiation by the cell–cell contact encountered competition between the adipogenic and osteogenic commitments. We also examined the effects of cell density, which involved both size and contact effects, and thus exhibited different behaviors under sole induction and co-induction as well. We revealed that the density effect reflected the cooperation (for adipogenic differentiation) or competition (for osteogenic differentiation) between cell size and cell–cell contact effects.