A breast implant

A breast implant is a prosthesis used in cosmetic surgery to enlarge the size of a woman's breasts (known as breast augmentation) or to reconstruct the breast (for example, after a mastectomy, or during male-to-female sex reassignment surgery). There are four types of breast implant:

Saline-filled, which have a silicone shell filled with sterile saline liquid. These implants are currently the only type available in the United States, but future regulation may make more available.
Silicone gel-filled, which have a silicone shell filled with silicone gel. In the 60 countries where silicone implants are available, they are used in approximately 90% of implant operations. The implantation of silicone gel-filled breast implants is currently illegal in the US.
String implant, a third, much less common type of implant, is a method of achieving extreme breast sizes, initially developed by Dr. Gerald W. Johnson, M.D.P.A., using polypropylene (PPP). String implants are unique in that they cause the breast to continue expanding after surgery, and are preferred by those women who choose to have the largest breasts possible, including many adult entertainers. String implants were eliminated years ago by the FDA due to the complications brought about by continuous growth after implantation.
Tissue engineered implant, a new form of implant currently in development. The principle is that cells are taken from tissue artificially grown from human stem cells, which are then combined with an appropriate scaffold material to produce a Tissue Engineered Breast Implant.[1] The advantage of this method is that there is no risk of leakage or rupture, and the size can remain stable for the lifetime of the patient, a contrast from the silicone or saline filled implants which typically reduce by approximately 40%.