Pluronic F127 is a surfactant and can lead to membrane disruption of some cells if the concentration is high. You may try using a lower concentration and see effect of conc. on toxicity.

I agree with Arun Iyer - the concentration you're working with could be the problem due to the reasoning he noted. Also keep in mind how the "pluronic gel" you mentioned is created and what it is made with - F127 on its own may be fine, but presenting it in a different format could impact its function and carryover from the gel formation process could also be harmful.

I'll add that pluronics are commonly used in cell culture (particularly shaker/bioreactors to reduce shear forces). In my experience, 0.1 - 2% of F68 is common in media for suspension-adapted HEK293 cells without hindered viability or growth.

F68 and F86 are mentioned in comments above. I'm just making sure one of these is not a typo. Are both comments relating us using F68?

Thank you for your help with this.