Design of suspension culture system with bubble sparging for human induced pluripotent stem cells in a plastic fluid.

ABSTRACT

Bubble sparging has been used to supply oxygen to large-scale bioreactor systems. However, sparged bubbles cause cell death by rupturing due to shear stress, and the foam layer carries a risk of contamination. Large-scale culture of human induced pluripotent stem cells (hiPSCs) is required for manufacturing, but hiPSCs show high sensitivity to shear stress, and also, aseptic processing is important for their expansion. In this study, a culture system with bubble sparging for hiPSC proliferation was designed using a plastic fluid as a culture medium. The rising bubble velocity in the plastic fluid decreased and was lower than that in a Newtonian fluid when the time interval between bubbles generation, Δt, was greater than 0.14 s. Under this condition, aggregate distribution in the plastic fluid was maintained without liquid flow. Although large aeration induced aggregate coalescence and growth inhibition, the apparent specific growth rate at Δt > 0.14 s increased with an increase in the aeration rate, and the maximum value was similar to that of the conventional suspension culture in a stirred bioreactor system. The gas hold-up in the plastic fluid was higher than that in a Newtonian fluid because of the lower rising bubble velocity, which leads to the suppression of bubble sparging. Therefore, our results indicated that using a plastic fluid leads to a more efficient oxygen supply without agitation in a spatial-temporal phase-transition culture system.