I was an electrician 25 years ago, but things have changed a bit

I am doing some framing with steel studs, and want to use ENT (you know, the blue plastic flexible stuff we called "smurf" when it first came out) to run the electric circuits. It's a semi-commercial application for a non-profit organization, and I can't use romex.
My questions is this: does code require bushings in the steel studs to protect the ENT?
Couldn't find it in the code book, and know that you guys are much more up on this than I
hey, thanks for any help you can offer.