Cell-culture additives — Pluronic F-68 protects mammalian cells from shear damage primarily because it is a non-ionic surface-active agent that does what?
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AStabilizes gas–liquid interfaces and foams, reducing cell–bubble adhesion and protecting cells during bubble rupture.
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BDestabilizes foams strongly, acting as a classic antifoam agent.
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CProvides essential vitamins to fast-growing cell lines.
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DActs as a coagulant to aggregate cells and debris.
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EEnhances impeller tip speed without changing power input.
Answer
Correct Answer: Stabilizes gas–liquid interfaces and foams, reducing cell–bubble adhesion and protecting cells during bubble rupture.
Explanation
Introduction:Pluronic F-68 (also called Poloxamer 188) is a widely used non-ionic surfactant in animal cell culture. The question examines why this additive reduces shear-related cell damage in aerated, agitated systems common to bioreactors and shake flasks.
Given Data / Assumptions:
- Suspension cultures of shear-sensitive mammalian cells (e.g., CHO, hybridoma).
- Aeration and agitation produce bubbles and gas–liquid interfaces.
- Pluronic F-68 is present at typical concentrations (e.g., 0.05–1.0 g/L).
Concept / Approach:Cell damage often occurs when cells attach to bubbles, are transported to the surface, and are ruptured upon bubble bursting due to high interfacial stress. A non-ionic surfactant adsorbs at interfaces, modifies surface tension, and forms protective layers that reduce cell–bubble adhesion and mitigate the violent stresses of bubble collapse. Although some antifoams break foams, Pluronic F-68 commonly stabilizes interfaces while protecting cells from interfacial trauma.
Step-by-Step Solution:Recognize the key damage pathway: bubble attachment and rupture at the surface.Identify surfactant action: adsorption at interfaces reduces direct cell–interface contact and stress transmission.Pluronic F-68 therefore serves as a shear protectant primarily via interfacial effects, not as a nutrient or coagulant.
Verification / Alternative check:Empirical studies show improved viability and titer upon F-68 addition under aerated conditions; microscopy reveals fewer cells associated with bubbles and higher post-aeration integrity compared with surfactant-free controls.
Why Other Options Are Wrong:
- (b) F-68 is not a strong defoamer; many silicone-based antifoams are used for destabilizing foams.
- (c) It is not a vitamin source.
- (d) It does not coagulate cells; excessive aggregation would harm mass transfer.
- (e) It does not affect mechanical speed directly.
Common Pitfalls:Assuming all surfactants are antifoams; overlooking that stabilizing interfaces can still protect cells by preventing harmful bubble–cell interactions.
Final Answer:Stabilizes gas–liquid interfaces and foams, reducing cell–bubble adhesion and protecting cells during bubble rupture.