The description below on saline implants is from the FDA ‘Guidance for Saline, Silicone Gel, and Alternative Breast Implants; Final guidance for Industry’ (1999). Link.

A silicone inflatable (saline-filled) breast prosthesis has a silicone shell made of polysiloxane(s), such as polydimethylsiloxane and polydiphenylsiloxane, that is inflated to the desired size with sterile isotonic saline before or after implantation. Most of these are single lumen devices with a valve that is sealable by the surgeon or self-sealing for the purposes of filling the prosthesis. The implants have a patch that covers the manufacturing port of the prosthesis. There are two types of saline-filled implants. One type is a fixed volume implant, which is filled with the entire volume of saline at implantation. Another type is an adjustable volume implant, which is filled intraoperatively and has the potential for further postoperative adjustment. Saline-filled implants vary in shell surface (i.e., smooth vs. textured), shape,profile, volume, and shell thickness.

The sterile saline used as a filler material should conform to United States Pharmacopeia (LISP) standards of Normal Physiological Saline (injection grade) which has a concentration of 0.15M and a pH of 7.2-7.4.

According to the FDA Office of Device Evaluation (ODE), the office responsible for conducting medical device evaluations and clearance for clinical trials and marketing, the following is what is in a saline-filled breast implant shell:

  1. 80% high molecular weight silicones
  2. 20% finely powdered silica (aka silicon dioxide)
  3. Catalyst of a tin or platinum
  4. Impurities: smaller silicones, volatile (readily evaporating) materials like xylene and other chemicals, and other heavy metals.