Melonie Charm has given the best explanation of the current state of affairs regarding the string implants.
If memory serves, the string implants went through a clinical trial phase. That phase is long over. The string implants were never approved, and as such were never disapproved.
After that, my memory gets murky. Something about needing $100,000 for the FDA to go through the hoops to get these approved, although I suspect I'm barely scratching the surface here.
Melonie if you're reading this, feel free to correct and clarify.