I found the solution of my problem,
The problem was that the parameters of material instance dynamic was not available and return empty at start of the game cause i needed to first create a material instance on my content browser and activate the parameter then create a dynamic material in my bluperint from the base of this material instance that i create before.
I don’t know if it’s a bug or somethings else but i found that few other people encounter the same issue.
This is a thread that help me : Possible to read the Parameter Name of a material using blueprints?
Hope that can help some people, and ty for your time.