Apparently polypropylene string has long been used in surgery for sutures etc, without issue, so it seemed the ideal candidate for a breast implant material if wadded up. These would be no capsular contraction, they couldn’t rupture like a normal implant could, they wouldn’t need replacing after a few years like a normal implant.

The idea behind it was sound, but then people’s breasts started growing out of control and so obviously the idea went no further and it was banned.