I don't think FBS is the issue, most likely you used a flask that was not treated with some coating materials that came with the flasks. You may use AddexBio Coat, a coating material that helps cells attach to a flask. here is the link: http://addexbio.com/...detail?pid=4666. Or else, just buy some new flasks that are cell culture treated. Best of luck.
I have used addexbio coat, and it works wonderfully for neuronal cells, they are cell culture ready, just dilute it to 1x and should do. here is the link: http://addexbio.com/...detail?pid=4666
Eviltwin: Hacat cells also require a rather high cell density to grow. If the density is too low, they do not like the environment and they start forming vacuoles. Nothing wrong with the cells, I believe.
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