Silicas
The term silica refers to the compound silicon dioxide, Sio2. Silica is a chemical substance with a lot of chemical, geological and commercial importance. It is the only source of elemental silicon, for commercial use, It is used in large quantities as a foundation of building materials, ceramics, concretes and glasses. In its various amorphous forms, it is used as an absorbent, reinforcing agent, binder, builder for detergents and as a catalyst component for support. Amorphous silica has the same basic atomic structure as crystalline silica but lacks a highly ordered geometry. Fumed silicas, which are amorphous, are generated by burning silanes and are used as reinforcing agents in many elastomeric and rubber silicone products.
(Silane= a discrete molecule whose structure us SiH4; also derivatives of this).
Silicone
Is the generic description for an entirely synthetic polymer containing a repeating Si-O backbone. The organic groups attached to the silicon atom via silicon-carbon bonds define the class of silicone. The most common example is poly-diethylsiloxane or PDMS. This is a synthetic polymer that has a repeating [(CH3)2SiO] unit. This is the basic building block of silicones. The number of repeat units in the chain and the amount of tying the chains together, six classes of commercially important products can be produced depending on certain variables.. They can be fluids, emulsions, compounds, lubricants, resins, and elastomers or rubbers.
Silicone Fluids
Fluids are usually straight chains of PDMS. These are teminated with trimethysilyl groups. PDMS fluids come in all types from water-like liquids to non-pourable fluids, and all of them are water insoluble.
Gels
Silicone gels are lightly cross-linked PDMS where the crosslink is achieved through either a "T" silicone structure or the chemical reaction between a vinyl group on one of the silicon atoms, with a hydrogen bonded to a silicon in a different part of the polymer. This chemical tying of siloxane chains produces a three-dimensional network which can be swollen with PDMS fluids to give a sticky, cohesive mass without form. Its physical appearance is controlled by the amount of crosslinking and how much fluid is added to the network.
Elastomers
Silicone elastomers are crosslinked fluids whose three-dimensional structure is much more intricate than a gel. There is very little free, non crosslinked fluid in the matrix. Amorphous silica is frequently added to the matrix to give greater reinforcement of the network and thereby increase he strength of the article.
Info. Excerpted from "Silica, Silicon, and Silicones...Unraveling the Mystery" paper by T.H. Lane , Ph.D. pf Dow Corning Corporation.
There are several processes that have been used in treating and making ready silicone for implants. The most common product of these processes in platinum-cured gel or liquid rubber, which was used in early implants. Other processes prepare the silicone for use in implants; however, all of these procedures require a final oven bake to ensure their purity and stability (jusbreastimplants.com). The types of materials used in implants are described in previous reports (Tinkler et al. 1993, Gott and Tinkler 1994). More detailed information about the complex chemistry of the silicones, i.e. the various silicone polymers used, as well as fillers (amorphous fused silica), coatings (e.g. a specific polyurethane) and adhesives, and about their manufacture is provided in published sources and private communications from manufacturers and other groups. Breast implants have changed in nature over a peroid. The earlier type comprised a silicone elastomer envelope containing a silica filler with attched Dacron sheeting, and containing a silicone gel. Later products consisted of a similar silicone elastomer envelope, also with Dacron attachments, filled with a silicone gel and sealed with a silicon polymer patch.The general experience has been that these silicone substances are, in reality, a small group of closely related polysubstituted siloxanes, containing simple alkyl groups for cross-linking and other purposes to control their physical properties. They are prepared from a small range of starting materials and are polymerised with a few specific reagents and catalysts to form polymers with specific properties. The gel used inside certain types of implant has an analogous composition. In addition, the outer membrane of polyalkylsiloxaneelastomer contains an inert filler, amorphous fumed silica, and a polyurethane coating has been applied to some products in the past. The adhesive is a further polyalkylsiloxane product, as in the patch used to seal the injection site in certain types of implant. The Dacron reinforcement has a long history of safe medical use. The analyses carried out on the breast implants cover the raw materials (monmers, crosslinking agents and catalysts, adhesives, amorphous fumed silica etc.), and various procedures applied to the final product.
component Typical Compounds Factors influencing residues or toxicity
base polymers dimethyl mostly incorporated into polymer; low polysiloxanes; molecular weight silicones are also included in gel
other polysiloxanes
additional polymers substitued polysiloxanes inc. into polymer to provide specific physical properties
crosslinking agents substituted polysiloxanes inc into polymer
filler/reinforcer amorphous, fumed silica or inc. into elastomer
timethylated silica
crosslinking catalysts platinum catalyst; stable platinum compounds are most commonly used
and reaction inhibitors tin catalyst (occasional); typically up tp 10ppm (0.5mg per implant). These
peroxide catalyst (rare); have different properties, particularly in terms of
organic inhibitors biochemical reactivity, and are much less toxic than
platinum compounds used as cytotoxic drugs.
solvents 1,1,1-trichloroethane; these organic compounds have low boiling points (up
xylene; acetone; ethanol to about 150C). They are effectively removed during
other solvents (occasional) processing for several hours at around 160C. Residue, where detectable, are typically below 10ppm and would rapidly be cleared by the body.
There are many risks involved with every surgical procedure including plastic surgery. Many breast augmentation risks can be avoided by choosing a qualified, board certified surgeon who is able to detect warning signs. As well as to effectively treat any unforeseen complications that can occur. In May 2000, the FDA approved the saline breast implants after finding they were a safe and effective means of achieving breast augmentations. The most common risks for a breast augmentation include:
Deflation, Detection of breast cancer becomes more difficult, Capsular contractive, Calcium deposits, Infection, Delay of wound healing , Neuroma, Additional surgeries to replace or remove the implant, Hematoma, Changes in breast sensation, the nipple and breast, Implant shifts, Bleeding Breast Asymmetry, Excessive scarring, Reactions to anesthesia.
