Polypropylene breast implants, also known as string implants, are a form of breast implant using polypropylene developed by Dr. Gerald W. Johnson. Due to a number of medical complications, the device has been banned in the European Union and United States. The polypropylene, which is yarn-like, causes irritation to the implant pocket which causes the production of serum which fills the implant pocket on a continual basis. This causes continuous expansion of the breast after surgery. Growth can only be alleviated by removal of serum by syringe.
Problems can also arise if the breasts enlarge at different rates. Continual breast growth eventually results in extreme, almost cartoonish breast sizes. String implants were only available for a very short time before being removed from the market by the FDA around 2001.