INTERACTIONS BETWEEN ANIMAL-CELLS AND GAS-BUBBLES - THE INFLUENCE OF SERUM AND PLURONIC F68 ON THE PHYSICAL-PROPERTIES OF THE BUBBLE SURFACE

We describe a method by which the degree of bubble saturation can be d etermined by measuring the velocity of single bubbles at different hei ghts from the bubble source in pure water containing increasing concen trations of surfactants. The highest rising velocities were measured i n pure water. Addition of surfactants caused a concentration-dependent and height-dependent decrease in bubble velocity; thus, bubbles are c overed with surfactants as they rise, and the distance traveled until saturation is reached decreases with increased concentration of surfac tant. Pluronic F68 is a potent effector of bubble saturation, 500 time s more active than serum. At Pluronic F68 concentrations of 0.1% (w/v) , bubbles are saturated essentially at their source. The effect of bub ble saturation on the interactions between animal cells and gas bubble s was investigated by using light microscopy and a micromanipulator. I n the absence of surfactants, bubbles had a killing effect on cells; h ybridoma cells and Chinese hamster ovary (CHO) cells were ruptured whe n coming into contact with a bubble. Bubbles only partially covered by surfactants adsorbed the cells. The adsorbed cells were not damaged a nd they also could survive subsequent detachment. Saturated bubbles, o n the other hand, did not show any interactions with cells. It is conc luded that the protective effect of serum and Pluronic F68 in sparged cultivation systems is based on covering the medium-bubble interface w ith surface-active components and that cell death occurs either after contact of cells with an uncovered bubble or by adsorption of cells th rough partially saturated bubbles and subsequent transport of cells in to the foam region. (C) 1994 John Wiley and Sons, Inc.