Effect of pulse frequency on the osteogenic differentiation of mesenchymal stem cells in a pulsatile perfusion bioreactor

Perfusion bioreactors are a promising in vitro strategy to engineer bone tissue because they supply needed oxygen and nutrients and apply an osteoinductive mechanical stimulus to osteoblasts within large porous three-dimensional scaffolds. Model two-dimensional studies have shown that dynamic flow conditions (e.g., pulsatile oscillatory waveforms) elicit an enhanced mechanotransductive response and elevated expression of osteoblastic proteins relative to steady flow. However, dynamic perfusion of three-dimensional scaffolds has been primarily examined in short term cultures to probe for early markers of mechanotransduction. Therefore, the objective of this study was to investigate the effect of extended dynamic perfusion culture on osteoblastic differentiation of primary mesenchymal stem cells (MSCs). To accomplish this, rat bone marrow-derived MSCs were seeded into porous foam scaffolds and cultured for 15 days in osteogenic medium under pulsatile regimens of 0.083, 0.050, and 0.017 Hz. Concurrently, MSCs seeded in scaffolds were also maintained under static conditions or cultured under steady perfusion. Analysis of the cells after 15 days of culture indicated that alkaline phosphatase (ALP) activity, mRNA expression of osteopontin (OPN), and accumulation of OPN and prostaglandin E(2) were enhanced for all four perfusion conditions relative to static culture. ALP activity, OPN and OC mRNA, and OPN protein accumulation were slightly higher for the intermediate frequency (0.05 Hz) as compared with the other flow conditions, but the differences were not statistically significant. Nevertheless, these results demonstrate that dynamic perfusion of MSCs may be a useful strategy for stimulating osteoblastic differentiation in vitro.