Additives for freely-suspended cells

Pluronic F-68, other phironic polyols, polyethylene glycol (PEG), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVIP) 

Two types of polyvinylpyrrolidones (PVP-Bayer, Leverkusen, Germany) have been found beneficial to cell growth in spinner cultures, and a mixed molecular weight PVP has been found to protect hybridoma cells against shear injury in a bubble column reactor (Handa, 1986). 

Polyethylene glycol (which is related in chemical structure to pluronic polyols) and PVA have been tested more recently as protectants against aeration and agitation cell damage (Michaels et al, 1991). Both appear to offer mechanical protection as good as F-68, without any detrimental effects on the cells they have been tested on (Chinese hamster ovary (CHO) and hybridoma cells CRL 8018). 

Viscometric studies are used to assess the shear robustness or fragility of cells by exposing them (usually for a short, 10-20 min, time period) to the reproducible and well-defined laminar flow of a viscometric device. In contrast, the (usually turbulent) flow in a bioreactor is not well defined and not easily reproducible, unless the same reactor is used. 

These findings suggest that the shear-protective effects of these additives in the bioreactor are physical in nature, and specifically purely fluid-mechanical, i.e. due to changes in the interactions between bubbles, draining films and the cells. If their effect was biological, cells would have been protected in both shear environments (viscometer and bioreactor). Other experiments suggest that the protection mechanism may vary for different cell types. 

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