I would say, no copper, absolutely not! It is a heavy metal- I wouldn't want to be taking any chances that your dear baby could/would/might somehow get to it. I'm not a real fan of anything that is not SS, though I do get donations that have things like nickel bells and stuff that I will use in non distructive birds and watch CLOSELY!
Here is an idea that I have been meaning to get around trying. A kids (the 2 legged variety) plastic slinky toy. My thought, was to cut off a right amount and make a sisal boing out of it. I am not sure what the metal ones are made of, I am almost sure its not ss! But, I haven't found the time to head into toys r us yet!
If you decide to try it and it works, let me know please!
Hope that helps!

J