Modification and qualification of a stirred single-use bioreactor for the improved expansion of human mesenchymal stem cells at benchtop scale

Background: To improve cultivation conditions for human bone-marrow-derived mesenchymal stem cells, we redesigned the commercially available UniVessel (R) SU bioreactor using results obtained from computational fluid dynamics. The goal was to produce >= 1 x 10(9) cells and to achieve expansion factors >= 30. Screening studies suggested that microcarrier solid fractions of at least 0.3% are required to reach the appropriate cell densities. Results: The fluid flow pattern found in the most promising modification (#2) was altered by increasing the impeller blade angle and lowering the off-bottom clearance. As a result, the maximum required specific power input was reduced by a factor of 2.2-4.6, depending on the microcarrier concentration, and peak cell densities were 3.4-times higher than in the standard version. Conclusion: The peak cell number of nearly 1.1 x 10(9) cells (expansion factor = 35), which was achieved in our low-serum cultivations, indicates an improvement in the redesigned UniVessel (R) SU configuration for bone marrow-derived mesenchymal stem cell expansions.