Surgical implants, silicones

Other surgical implants are essentially plastic repair products for worn out parts of the body. It is possible to conceive of major replacements of an entire organ such as a kidney or a heart by combining the plastic skills with tissue regeneration efforts that may extend life. This is used to time the heart action. Extensively used are plastic corrugated, fiber (silicone or TP polyester) braided aortas (24). 

The Monsanto project is said to have been canceled, despite the effectiveness and designed environmental friendliness of the products, because of the sinister reputations (not wholly deserved) of both asbestos and phosphates in the popular view. A similar problem with public perception of silicone surgical implants was noted in Section 3.5. The tenor of our times is such that much beneficial technology may be lost through litigation (or the mere fear of it) regardless of any favorable scientific evidence that is put forward. 

The most common compounds used for implants are silicones, fluoropolymers, and polyurethanes. Although at one time silicone implants were thought to lead to autoimmune and rheumatic disorders, these studies were likely flawed and such compounds are now once again used for surgical implants.58... 

Besides external contact lenses, there are surgically implanted intraocular contact lenses that are usually used to replace the eye s natural lens after cataract surgery these lenses are normally based on silicone or PMMA and lie outside the scope of this entry. 

Surgical implants, female breast reconstruction, silicone (Vol. 74 1999)... 

Silicone elastomers are noted for high temperature and oxidative stabihty, low temperature flexibility, good electrical properties, and high resistance to weathering and oil. They are used in wire and cable insulation and surgical implants and as material for gaskets and seals. 

Alan Chow from Optobionics spoke about his Artificial Silicon Retina (ASR) [14], ASRs are semiconductor-based silicon chip microphotodiode arrays (microscopic solar cells) designed to be surgically implanted into the subretinal space. The arrays are approximately 2 to 3 mm in diameter, 50 to 75 /um thick. Dr. Chow reported successful electrical stimulation of normal animal retinas. 

When implanted, silicone rubber is slowly calcified and thus rigidified through a mechanism that has not been elucidated. Despite this drawback, there is presently no alternative to the use of silicone rubber, but it should be used only under appropriate conditions, i.e. the bags should be thick enough and filled with aqueous solution, and there should be no talc on the surgical gloves. 

Silicones are apparently completely non-toxic. Silicone rubbers have been used to make surgical implants for the human body. 

Fig. 4. Artist s drawing of the stimulator, silicone rubber tube or guidance channel, and the electrical circuit within the spinal cord. The tube was implanted into the dorsal spinal cord. The uninsulated tip of the cathodal electrode (negative) was sealed within the center of the tube, while the anodal electrode (positive) remained outside the vertebral column, sutured to paravertebral musculature. The body of the stimulator was surgically placed within the fat pad at the base of the guinea-pig s neck. To complete a circuit, current must flow initially into each end of the hollow tube as diagrammed. For diagrammatic purposes, the drawing is not made to scale. [Reproduced with permission from Borgens (1999).]...

The electrodes are manufactured and distributed by MEDTRONIC (Minneapolis, USA). The epidural implantation is performed under local anesthesia. The second electrode type consists of four platinum disks that are embedded in a silicone rubber carrier. They have a diameter up to 6 mm (Fig. 7). They are implanted close to the spinal cord under complete ane sthesia. Surgical procedures have been developed from the early 1970s up to the present [43]. Current designs offer the possibility of externally correcting small dislocation of electrodes [44]. Meanwhile more than 300 patients have benefitted from this therapy. 

Silicone was first used for breast implants in the 1960s for women who had undergone mastectomies, surgical removal of their breasts. Silicone implants later became popular with women who had no medical problems, but wanted larger breasts. By the 1980s, many women with breast implants... 

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