Chemical Concepts
Silicone materials exhibit unique properties based on their chemical structure. The silicones have the water-resistant hydrocarbon groups arrayed along the outside of the chain of Si-O atoms.  Cells do not attach themselves to the silicones.   Chemists could make high molecular weight polymers and low molecular weight fluids.

This is about silicones as breast augmentation implants.
a. History of Silicones
b. Implants as Hydrocephalic Shunts
c. Breast Implants
d. Medical Questions Arise
a. History:
GE  first developed practical silicones.  Corning Glass - once cooperative with GE on silicones -  went its own direction with silicones.  They went into competition with General Electric.  The giant glass company lacked the chemical expertise to develop silicone polymers or to manufacture them efficiently so they turned to Dow Chemicals for help.  Dow and Corning formed a partnership in 1943. This joint venture would be a separate company, owned by Corning and Dow, called appropriately, Dow Corning. 
 

After World War II and the Korean War, our nation experienced heady times.  America prospered; we built structures like the interstate highway system.  Scientists and engineers and manufacturers had new materials for building blocks: Wallace Carothers had invented  nylon;. Speed Marvel led the invention of synthetic rubber; Eugene Rochow invented silicones.

b. Implants as Hydrocephalic Shunts:
Dow Corning took their silicones into a new field for synthetic materials--medicine.  Medical scientists were  looking to the arsenal of materials that chemists were making to improve medicine.  After all, surgeons still used "catgut" sutures, the processed intestinal walls of sheep or cows, to sew wounds together.  In many ways, the practice of medicine had not changed in centuries.

Dow Corning scientists and academic physicians and research scientists looked at silicone material for medical applications. Silicone’s chemical and physical properties seemed attractive for medical devices.  Chemically, silicones seemed inert, so they might not react with the chemicals in the body. Silicones' high temperature stability suggested they might be easily sterilized should the physicians wish to use them during surgery, or even implant them in the body.
 

Medical success came quickly.  Dow Corning cooperated with Doctors F. E. Nulsen and E. B. Spitz to develop the hydrocephalic shunt, a silicone rubber tube placed into a child’s head to relieve hydrocephalus, that is, "excess of cerebrospinal fluid in the cranial cavity causing enlargement of the skull and resulting in mental retardation."

What was critically important was that, in the more than 4,000 shunts implanted, the silicone worked well.   Surgeons had a look at a couple of implants after they had been in the body for a long time.  The silicone materials caused no reaction in the tissue surrounding the implant.

Scientists note facts like that.  Silicone rubber's stability in the human body suggested that the other forms of silicone products, particularly the rubbers, resins and fluids, might be useful as medical devices that could be implanted.

c. Breast Implants: 
Dow Corning offered silicone materials to two plastic surgeons, Thomas Cronin and Frank Gerow of the University of Texas who developed a silicone breast implant in about 1960.  Their  implant was developed for use by women who had had breasts removed in the surgery called mastectomy.  The new silicone implants replaced sponges that had been used previously. The spongy implants hardened and looked and felt less natural after a period of time.   The silicone rubber sac filled with silicone gel was called a mammary prosthesis.  Dow Corning marketed the Cronin implant in 1964, two years after the first human trial implant. Thousands and thousands of women elected silicone implants. 
 

Meanwhile, the government's National Institutes of Health (NIH) began implanting the whole series of new polymers in animals to determine how living tissue behaves in the presence of these foreign materials.

Their objective was clear:  If these synthetic materials could be tolerated in tissue, this might lead to many new ways to use the materials in the body.  The NIH studies showed that a whole series of familiar synthetic materials, nylon, Teflon®, Mylar®, polyester, silicone and polyethylene, could be implanted in animals over a long period of time with minimal  irritation or other physical response.  The excellent implant behavior of a number of materials fueled the thinking that most synthetic polymers would be safe.

(You can check recent work by NIH on implants by searching the NIH website).

During the 1960's, Dow Corning improved the tactile properties of their  breast implant device. They eliminated a seam and made the outer sac thinner.  Other manufacturers joined Dow Corning in the rapidly growing implant market.  Dow Corning made additional changes during the 1970's.

In 1977, a woman who claimed her implants had ruptured, received a $170,000 settlement of a law suit from Dow Corning. The U.S. Food and Drug Administration, which had been quiet on the issue of implants, changed its policy and demanded more safety information from implant device manufacturers.  But the silicone breast implants were not impacted by the FDA decision.