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Part 4: DOW CORNING'S CONTRIBUTIONS TO SILICONE IN MEDICAL PRODUCTS[15]
Throughout the 1950’s and 1960’s, Dow Corning, as well as independent medical doctors and research scientists, performed scientific tests on silicones, evaluating it and sometimes using silicone material for medical applications. The Center's newsletter, The Bulletin, reported results of these tests from October, 1959 to July, 1972, including both Dow Corning and outside researchers' findings. Several of silicone’s characteristics make it suitable for medical products. It is usually considered chemically inert, so that it will not react with the wide range of chemicals present in the body. It can endure extreme temperature fluctuations without changing consistency. This thermal stability is especially important to the medical world, since it can therefore be sterilized at high temperatures. Finally, silicone is water insoluble, and thus is a good candidate for use in water-based environments, such as a woman’s breast.
Through their Center for Aid to Medical Research, CAMR, Dow Corning invented many important medical devices. For example, first introduced in the late 1950’s, Dow Corning created the hydrocephalic shunt, a silicone drain implanted in a child’s head to relieve the effects of hydrocephalus, "an excess of cerebrospinal fluid in the cranial cavity causing enlargement of the skull and mental retardation"[16]. In 1952, Doctors F. E. Nulsen and E. B. Spitz originally developed the technique of treating hydrocephalus by inserting a valve into the skull, diverting the excess water from the ventricle to the jugular vein. Later, they used a shunt valve developed by Dow Corning and John Holter, with encouraging results [17].
In the January, 1960 edition of the The Bulletin, W. E. Wallace, MD, of the US Air Force Department of Neurosurgery in the Medical Corps, reported, "It has been my good fortune, however, to utilize the Spitz-Holter valve for hydrocephalus in 29 patients. Some of these patients came to re-operation, and it was possible to visualize the Silastic® .[18] tubing used. In none of these cases was there any apparent tissue reaction to the silicone materials."[19]
Such medical breakthroughs were not introduced without testing. For example, the Dow Corning CAMR January, 1960 newsletter describes a scientific evaluation of silicones as organic tissue substitutes:
Of the many synthetic materials we have investigated during the past nine years, including halogenated hydrocarbons and polyvinyl alcohol, silicones have proved most promising in clinical use. . . [20]
-"Evaluation of silicones as tissue substitute"
In the same newletter, "An experimental study of silicone as a soft tissue substitute" stated:
. . . seven healthy adult mongrel dogs were used . . . At time intervals varying between 3 months and 1 year the sponges were removed . . . Reaction at this stage is mostly one of fibrosis rather than exudation or foreign body reaction. Sponged Silastic® 250 and s=9711 (red and gray) implants observed in the gross showed almost no tissue reaction. There appeared to be more reaction to the 4-0 silk anchoring sutures than to the implant itself. . . These studies indicate that clinical applications now served by silicones are justified.[21]
Other uses include silicone's presence in cardiac catheters, where, ". . . Neither oily nor greasy to the touch, such a silicone surface is said to reduce markedly the tendency of blood to clot in contact with the catheter"[22]. Related to this, silicone has been successfully used to treat coronary air embolisms, where air bubbles lethally interfere in the blood flow of arteries to the brain or heart.
But what about long-term effects? How were the hydrocephalic patients doing, not just three months after surgery, but more than a year? In the October, 1960 newsletter, we find R. H. Ames, MD, reporting on Silastic ® tubing:
Clinical experience indicates that Silastic® is extremely well tolerated. I now have patients in whom these materials have been implanted for upwards of three years without evidence of ill effects. Recently the opportunity presented itself to re-examine a ventriculocisternostomy performed in 1957. . . no adhesions were in evidence, and the silicone rubber tubing was unchanged by three years implantation in the tissues of the brain. . . [23]
Furthermore, this October, 1960 newsletter also contains Part One of an article on the study of the toxicology of silicones by R. R. McGregor, Ph.D., of the Dow Corning CAMR. Indeed, 5 years prior to the commercial marketing of the breast implant, "With the exception of some very low molecular weight materials, silicone fluids were found by Rowe, et al. to cause little response in laboratory animals when injected subcutaneously, intramuscularly or intraperitoneally."[24] Subcutaneously means situated beneath the skin. Intraperitoneally is within the abdomen. Intramuscularly indicates something injected within the muscles. Such muscles include the heart, where the well known life-saving pacemaker, clothed in silicone, is placed. At that time, 30 such units had been tested: "Most recent publication describes the implantation of such devices in six patients. All were alive with results extremely gratifying in five of them. One completely disabled patient, in his middle thirties, was rehabilitated."[25]
Indeed, Dow Corning researchers were not the only scientists interested in the medical possibilities of silicone. Research on the potential uses of silicone in medicine, and reactions of animals to it, had been performed since the 1940's and 1950's. For example, in February, 1952, Windsor Cutting, MD published an article in the Stanford Medical Bulletin entitled "Toxicity of Silicones," studying the silicone used as a food additive to control foaming. Unlike previous studies which had found no lesion development due to the ingestion of silicone by rats, his study found such a reaction in rabbits fed silicone along with a high cholesterol diet[26]. In August, 1959, the article, "Tumors Associated With Embedded Polymers,"[27] appeared in the Journal of the National Cancer Institute. It found that only five rats out of the 299 that lived at least three-hundred days with certain polymers, including various Silastics®, developed tumors, that is, only 1.7 percent. However, this percentage was lower than similar studies' results, so the authors suggested that more research was needed.
In the July, 1961 edition of The Bulletin we find an abstract of Midland Silicones, Ltd.'s[28] work , "A Note On Bacteriological Toxicity Tests Of Silicone Rubbers For Medical and Pharmaceutical Uses." (Written by I.H. Riley and H.I. Winner, it was published in the Journal of Pharmacy and Pharmacology.) It states: "In the great majority of cases. . . there was no inhibition at all. This complete lack of toxicity was true of the uncured rubber as well as pieces given all degrees of cure"[29]; and "the toxicity of suitably compounded rubbers which could be used in pharmacy, medicine and in contact with food stuffs . . . [was] . . . very low"[30]. Other studies supporting the low toxicity and carcinogenesis of silicone followed[31]. By 1962, a study entitled "Tissue Reactions to Polymers" published in the British medical journal, The Lancet, stated:
For clinical use a polymer must consistently prove innocuous. Of the polymers examined in the present series those which produced consistently good results were the silicones and the medium-density and low-density polyethylenes. . . None of the other types of plastic investigated produced completely consistent results [32].
Thus , silicone's performance in medical applications was of interest to the global medical community, not just to suppliers like Dow Corning.
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