Osteoblast response to continuous phase macroporous scaffolds under static and dynamic culture conditions.

Average scaffold pore sizes in the order of several hundred microns are generally required for efficient bone tissue ingrowth in vivo, whereas the culture of large bone engineering constructs in vitro can require bioreactor cultures to decrease diffusional constraints on the cells. In this study, we prepared poly(epsilon-caprolactone/D,L-lactide)-based scaffolds with continuous phase macroporosity using a novel CaCl(2) . 6H(2)O porogen agent. Osteogenic differentiation and scaffold colonization in rat bone marrow stromal cell cultures were compared in such polymer scaffolds, and in composites with 30 wt % bioactive glass filler. The effect of a rotating wall bioreactor culture on the cell response was also evaluated. Bioactive filler enhanced proliferation, early osteogenic differentiation, and mineralization of the cultured cells under static conditions. Dynamic cultures, in turn, resulted in decreased cell numbers and inhibition of the differentiation process irrespective of the scaffold type. This effect was ascribed to the harsh mechanical stresses caused by constant collisions of the scaffolds in the bioreactor vessels. However, cells were able to penetrate into the scaffold interior only under dynamic culture conditions. Thus, interconnected macroporosity is an essential, but not sufficient, condition to allow for full colonization of millimeter scale tissue engineering scaffolds in vitro.