Capsular Contracture - The Fallacies of Its Reduction by the Use of Silica Free Coatings

W. LYNCH

The silicone gel implants contained in a silicone elastomer shell as they are currently produced are good products. Over the past few years, when used by expert plastic surgeons, remarkable results have been achieved.

Recently a mammary implant has been introduced having an outer coating of silica free silicone polymer. The manufacturer purports this to have improved bio-compatibility based on reports by Kolobow et al l, 2 on exposed silica having a detrimental effect on blood compatibility. Therefore, by insinuation, the silica free coating will aid in preventing capsular contracture. Kolobow has reported the successful casting of membranes, for use in blood oxygenators, from silicone rubber dispersion as thin as 9um (.0004 in.) where potential exposure of aggregated filler particles becomes a distinct possibility. Unlike the Kolobow membrane which is supported by fabric and is relatively stationary in use, the shell of the implanted mammary is subjected to a great variety of continuous flexing, folding, and pressure. It is generally known that silicone rubber lacks flexibility and toughness when it does not contain reinforcing silica filler. Therefore, a silica free layer even when applied over a reinforced layer when subjected to such stresses is certainly prone to degradation.

Reference is also made to the paper by Gifford et al3 in which it is suggested "that cured silicone rubber without filler causes less tissue reaction than that with filler". The filled and unfilled materials used in this study were not only made from dissimilar silicone base rubbers but by different manufacturers. The authors also assumed that radiation cross linking which they used, left no molecular residues in the silicone rubber. This is incorrect. Warrick4 and others 5,6 have detected that a variety of degradation products are formed depending on conditions of radiation or heat aging. Other radicals than methylene are no doubt produced. These could conceivably bind to the filler changing the biocompatibility of the vulcanized material.

At least one plastic surgeon, who has tried the silica free coated device, reported one type IV contracture in four cases over a six month period7.

Through the use of electron miscroscopy and energy dispersive Xray analysis, a number of researchers 8,9 have reported the presence of vacuoles in capsular material surrounding gel filled implants. The vacuoles appear as amorphous droplets 1 to 25 um (um= micrometer or .001 millimeter - .00004 in.) in diameter. The presence of the element silicone can be detected in these droplets by Xray analysis. It can be reasonably deduced that the silicon is present as silicone gel constituents, since silica filler particles are generally in the range of 10 to 15 nanometers in size or approximately 1-100 the size of the smallest vacuoles and exhibit different optical properties. The electron microscope studies of capsular tissue made by MEC involved the first time use of an EMMA 4 (Electron Microscope Microprobe Analyzer), a much more sophisticated micro analytical tool than either the standard transmission or scanning type of electron microscopes. This work left little doubt that the vacuoles were filled with dimethylsiloxane material. There was no detection of silicon as Si02 in the capsular tissue by this method. Furthermore, it has been well documented clinically that the presence of these silicone filled vacuoles cannot be related to capsular contracture9 nor can the thickness of the capsule 10

A careful study of the literature will show that the etiology of constrictive capsule formation is perplexing 10,11 and most of the theories of contributing phenomena, including the possible role of silica filler, are quite subjective. Much more scientific research must be done before a reasonable understanding of this apparently multifaceted phenomenon is achieved. In the belief that increased research covering the causes of capsular contracture will lead to its improvement. MEC has an ongoing scientific program to study the effects of silicone implants on human tissue and the organs of the body as a whole.


REFERENCES

1. Kolobow, T., Stool, E.W. Weathersby, P.K. , Pierce, J., Hayano, F., and Suaudeau, J.: "Superior Blood Compatibility Of Silicone Rubber Free Of Silica Filler In The Membrane Lung", Vol. XX Trans. Amer. Soc. Artif. Int. Organs, 1974: p. 269 - 276.

2. Kolobow, T., Tomlinson, T.A., and Pierce, J.E.: "Blood Compatibility of Methyl, Methyl Vinyl, Methyl Phenyl, and Trifluoropropylmethylvinyl Silicone Rubber without Silica Fillers in the Spiral-Coiled Membrane Lung", National Heart and Lung Institute, 3. Biomed. Mater. Res., Vol. 11, pp. 471-481 (1977)

3. Gifford, Jr., 0. H., Merrill, E. W., Morgan, M. S.: "In vivo Tissue Reactivity of Radiation-Cured Silicone Rubber Implants", 3. Biomed. Mater. Res., Vol. 10, pp. 857-865 (1976)

4. Warrick, E.L.: "Effects of Radiation on Organopolysiloxanes", Industrial and Engineering Chemistry, Vol. 47, No. 11, pp. 2388-2393.

5. Atkins, D.C., Murphy, C.M., and Saunders, C.E.: "Polymethylsiloxanes... Thermal and Oxidation Stabilities", Industrial and Engineering Chemistry, Vol. 39, No. II, pp. 1395-1401 (1947).

6. Charlesby, A.: "Silicones", Atomic Radiation and Polymers, pp. 297-311 (1960).

7, Dow Corning, "Fact Sheet", ASPRS Meeting, November 1978.

8. Wickham, 0., Rudolph, R. and Abraham, 3.: "Silicon Identification in Prosthesis- Associated Fibrous Capsules", Science, Vol. 199, 27, Jan. 1978: 437-438.

9. Rudolph, R., Abraham, 3., Vecchione, T., Gruber, S., and Woodward, M.: "Myofibroblasts and Free Silicon Around Breast Implants", Plastic and Reconstructive Surgery, pp. 185-196, Aug. (1978)

10. Smahel, J.: "Histology of the Capsules Causing Constrictive Fibrosis Around Breast Implants", British Journal of Plastic Surgery, 1977, 30: pp. 324-329

11. Wagner, H., Belier, F., and Pfautsch, M., "Electron and Light Microscopy Examination of Capsules Around Breast Implants", Plastic & Reconstructive Surgery, Surgery July 1977: p. 49-55.

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