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?

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.