PROTECTION MECHANISMS OF FREELY SUSPENDED ANIMAL-CELLS (CRL 8018) FROM FLUID-MECHANICAL INJURY - VISCOMETRIC AND BIOREACTOR STUDIES USING SERUM, PLURONIC F68 AND POLYETHYLENE-GLYCOL

We use bioreactor and viscometric studies to examine the mechanism by which three additives, fetal bovine serum (FBS), pluronic F68, and polyethylene glycol (PEG), protect the freely suspended CRL-8018 cells from damage due to interactions with bubbles in agitated bioreactors. In bioreactor studies, the protective effect of an additive could be due to either changes in the ability of the cell to resist shear (biological mechanism) or to changes in the medium properties that affect the level or frequency of forces experienced by the cells (physical mechanism). Bioreactor studies show that protection by all three additives occurs whether the cells are grown in the presence of the additives (long exposure) or the additives are added to the medium after the cells were exposed to detrimental agitation intensity (short exposure). In the viscometric studies, exposure of cells to laminar shear in the absence of gas-liquid interfaces assesses only the ability of the cells to resist a constant level of shear in a medium with or without an additive. Viscometric studies show that prolonged exposure to FBS makes the cells more shear tolerant, but that short (30-120 min) exposure to FBS does not affect their shear tolerance. We thus conclude that the protective effect of FBS in bioreactors is of both physical and biological nature. The biological contribution is metabolic in nature rather than fast acting. Viscometric studies show that either long or short exposure of the cells to either F68 or PEG does not make the cells more shear tolerant. We therefore conclude that the protective effect of F68 and PEG in bioreactors is physical in nature.