Effect of gas—liquid interfaces on the growth of suspended mammalian cells: mechanisms of cell damage by bubbles

The hypothesis is examined that cell death in sparged systems for suspended mammalian cell culture is associated only with the region of bubble disengagement at the medium surface. The effects of bubble diameter, superficial gas velocities, and the nonionic surfactant Pluronic F-68 on hybridoma viability have been reported previously. The work reported here extends these experimental studies to a range of bubble columns and for the culture of not only hybridoma but also myeloma, BHK-21, and lymphoblastoid (RAJI) cells lines. In short bubble columns, small bubbles and high bubble frequencies are more detrimental to hybridoma cells than BHK-21 suspension cells. Both fetal calf serum (FCS) and Pluronic F-68 have concentration-dependent protective effects on cells. In defined serum-free media, gross mechanical disruption of hybridoma cells and loss of cells and medium components at the medium surface occur on sparging. With increasing bubble column height, a progressively increasing retention of cell viability is observed for all cell types. By implication, this is because the proportion of time spent by cells in the “destructive zone” at the medium surface is reduced as the column height increases. Finally, two mechanisms of cell damage are proposed: damage due to rapid oscillations caused by bursting bubbles, and damage due to shearing in draining liquid films (or lamellae) in foams. It is proposed that Pluronic (and other polymers such as polyethylene glycol and polyvinyl pyrollidone) act as cell protective agents by stabilizing foams and thereby reducing film drainage and bubble bursting in the vicinity of cells.