Safety of Silicone Breast Implants (1999) / Chapter Skim
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2 Silicone Chemistry
2 Silicone Chemistry
Pages 39-53
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From page 39... ...
atoms linked by oxygen (O) atoms in a 2:1 ratio; each silicon atom is linked to four oxygen atoms, and each oxygen to two silicon atoms.
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From page 40... ...
Sodium and calcium oxides are used as diluents in sodalime window and bottle glass. Silica aerogel, silica smoke, fumed silica, and precipitated silica are names for amorphous silica powders that are important constituents of medical rubber-like goods, including breast implants.
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From page 41... ...
and is absorbed from the gastrointestinal tract, whereas compounds with 3,000 units are relatively inert biologically and are solids having viscosities of millions of centistokes (see Chapter 4 and Table 2-1~. CHEMISTRY OF SILICONES Silicone is made by the reaction of dimethyldichlorosilane (Me2SiCl2)
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From page 42... ...
A high temperature flame of this tetrachlorosilane reacting with steam gives a white amorphous silica smoke or aerogel, which is gathered to provide the very finely divided filler used in silicone rubber. FUNCTIONALITY AND NOMENCLATURE Another shorthand polymer nomenclature is useful as well.
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From page 43... ...
and Q control molecular weight, branching, and molecular shape and are used to formulate various types of silicone resins (varnishes, fiberglass bonding solids, pressure-sensitive adhesives, and even the release paper for protecting adhesive tapes)
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From page 44... ...
For even higher purity, a technique called zone refining has been used to form polymers of more than 40,000,000 Daltons (Martellock, 1966~. The D4 tetramer is an eight-membered ring of alternating silicon and oxygen atoms with eight methyl groups attached, two per silicon (octamethylcyclotetrasiloxane)
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From page 45... ...
A list of silicone containing medical devices includes hydrocephalus shunts, foldable intraocular lenses, soft tissue implants for congenital and cancer reconstructive surgery, cardiac pacing and defibrillation devices, implantable infusion pumps, elastomeric toe and finger joints, in
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From page 46... ...
has a very low surface energy, which causes it to spread on higher-energy surfaces and to make these surfaces water repellent. Silicone resins, highly cross-linked with T or Q units to give the required hardness, also have this effect and are used to coat plastic eyeglass lenses, or glass bottles with a very thin film to increase scratch and break resistance and aid in emptying aqueous contents.
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From page 47... ...
See Table 2-2 for the composition of several versions of the Dow Corning gel. Certain silicone fluids, chainstopped with alkyltriacetoxysilane and thickened with amorphous silica filler, cure to RTV silicone rubbers when exposed to moist air.
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From page 48... ...
48 V - , in, _ I ~ ~By ~ ~ of ° ~ ~ ~ ~ 5 o cn cn ~ _ 5- 5 Lr)
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From page 49... ...
All three types of elastomeric materials have been used to produce silicone breast implants, joint implants, surgical drains, pacemaker covers, indwelling catheters, and the like (Batich and DePalma, 1992; Batich et al., 1996; Clarson and Semlyen, 1993; Kennan and Lane, personal communication, 1998~. SILICONE BREAST IMPLANTS The chemistry of silicone elastomer and gel in a silicone breast implant described here is based substantially on disclosures by Dow Corn
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From page 50... ...
The earliest Dow Corning shells were made of high molecular weight polymer (gum) filled with amorphous silica and a process aid designed to passivate the filler surface.
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From page 51... ...
The network gel, 20% of the material mass, is a single giant molecule that is swollen by low molecular weight fluid, which compromises 80% of the mass, that can move or be extracted like water in a sponge. BARRIER-LAYER IMPLANTS The movement or diffusion of silicone gel fluid was addressed by Dow Corning with a fluorosilicone elastomer barrier-layer shell.
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From page 52... ...
52 on ~ o ~ o Do o 1 ~ u be cry H Cal ¢ Em o U U ·_1 o ~ON O COO ..
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