James J. Romano, MD
The first augmentation mammoplasty dates back to 1895, when a fatty tumor (lipoma) was transplanted from a woman’s back to the breast area. The use of prosthetic materials for breast implantation dates to the mid-1500s, when substances such as ivory, glass, and paraffin were used. Silicone as a medical implant first began to be used around 1940. Later, sponges made from Ivalon, Etheron, Teflon and polyurethane became popular as breast implants but were quickly abandoned due to an unacceptably high rate of severe hardening, contracture, and disfigurement. Progressive demand for softer and more natural implants led to the development and use of a sealed silicone-gel prosthesis in 1962. From this start, five different basic types of silicone implants became available over the years: 1) gel-filled 2) double-lumen inflatable (mostly gel-filled, but a small space to add some saline) 3) saline inflatable 4) textured silicone gel and 5) polyurethane-covered silicone gel. In 1992 the FDA restricted the use of silicone gel-filled breast implants.
The saline-filled breast implant as an inflatable prosthesis was introduced as far back as 1965. Its initial popularity was dampened early on by reports of numerous occurrences of deflation. The valve was redesigned but not until many early users switched to silicone gel. Despite this, many doctors have only used saline-filled breast prostheses. Like most medical devices, saline-filled implants have improved dramatically in both production and design since their introduction. Modern saline implants have redesigned fill-valves and seals that rarely leak or deflate. Current statistics suggest a less than one-percent deflation rate over at least a ten-year period. The shell of a saline-filled implant is made of a silicone elastomer, which is a soft, rubbery membrane. Today’s devices may have either a smooth surface or a textured coating thought to minimize capsular contracture. Different shapes include round flat, round conical, anatomic narrow, and anatomic wide. There are different types and degrees of surface texture. Saline is medical grade saltwater solution of the same approximate concentration as the fluid component of our bloodstream. It is harmless if it leaks. There is less than a natural feel to saline implants, edges may be palpable, wrinkles may be visible, mammography is still partially obscured, and deflation, although rare, may still occur. So despite a 30+-year track record of effectiveness and safety with the saline implant, there is ongoing research and investigation geared toward development of a more “ideal” breast implant.
The ideal filler material would be radiolucent (allow for better passage of x-rays for mammography), viscosity similar to breast tissue, biocompatible, nontoxic, inexpensive to produce, and stable long term. Not to mention “user-friendly,” “environmentally kind,” and “media-proof.” At this point silicone elastomer is still the material used for the shell.
Polyethylene glycol (PEG) is a nontoxic, nonimmunogenic, noncarcinogenic material currently under investigation as an additive to saline in breast implants. It is the active ingredient of GoLYTELY, a popular bowel preparation. Its major reported advantage as a filler additive is to increase viscosity without further interfering with mammography. It is currently under clinical trials in Europe.
Lipo-Matrix is a material made by Collagen Company and available as the Trilucent Adjustable Breast Implant. It is available only for patients with problems from previous implants. There is a silicone shell filled with a biocompatible triglyceride derived from soybean oil. It is less viscous than silicone or PEG. Most surgeons feel it does not offer any advantage in terms of feel or shape. It does offer better radiolucency than silicone, but still not as good as saline.
Hyaluronic acid is a naturally occurring polysaccharide molecule and under investigation as an implant filler. This is placed into a silicone shell, and is more radiolucent than saline or silicone. It is currently not available.
A hydrogel substance is currently under development by the implant manufacturer Mentor Corporation as an additive to silicone shells. The exact composition has not yet been revealed but it is well metabolized by the body and has good viscosity. It is currently available in Europe and an investigation application on file for use in the United States.
Other substances under investigation with even less known about them are methylcellulose, neutral triglyceride, polyvinyl pyrrolidone, polyvinyl alcohol, marine gel (seaweed), peanut oil triglyceride, and soybean oil triglyceride.
New approaches are also being tried to make silicone gel “safer.” This mostly involves using a more cohesive silicone, which is a firmer gel—almost hard. It would not ooze or leak like a liquid can.
Despite all of the investigations, there is still controversy regarding the immunogenic potential of these natural substances. Soybean oil, for instance, is considered safe and has been used extensively for IV calorie replacement in malnourished patients. However, safety when used in an IV is far different than the harm that can be done when this same substance is leaking or “bleeds” from an implant shell and then becomes a substance of chronic lymphatic uptake. There is also the issue of degradation and possible rancidity of these substances over time. For example, many of these oils normally have an expiration date, so rupture beyond this time may expose the body to rancid oils.
At this time, none of these substances are anywhere near close to becoming available or widely popular in the US. Saline-filled breast implants are still the best product.