Biological effects of silicone gel sheeting.

Since silicone gels were first used in the treatment of hypertrophic scars (HS) and keloids (K) they have proved useful and safe. Depending on the specific investigation, the application of silicone gels showed improvements in redness, itching, texture and thickness of HS and K in 60% to 100% of cases. Generally, texture was the first scar characteristic to change, followed by color and height. Despite silicone gels wide use in the treatment of HS and K, and the many studies that have been performed in the past 2 decades, the mode of action of these materials remains poorly understood. This knowledge is even more difficult to obtain because the pathogenesis of HS and K is still unclear. Moreover, terms are sometimes used interchangeably, making it difficult to compare results on the effect of treatments among different studies. However, criteria to differentiate HS and K have recently been reported, and it has been hypothesized that immunologic mechanisms could be involved in the development of HS and K. Furthermore, we demonstrated the presence of an immune cell infiltrate in HS and K and characterized the immunophenotypic features of this infiltrate, which are indicative of a delayed type immune reaction. HS and K show distinct immunophenotypic profiles, and the amount of the immune cell infiltrate is related to the age and the clinical behavior of HS. It has been reported that silicone gel softens and reduces HS in a shorter period of time than pressure therapy and that the results obtained are not due to pressure, temperature, or oxygen tension. However, it has also been reported that temperature differences of less than 1 C, as found under silicone gel sheeting (SGS), can have a significant effect on collagenase kinetics and may alter scarring. Elasticity, measured by elastometry, is significantly increased in SGS treated HS compared with control lesions. In a recent study, we performed an investigation to evaluate the efficacy of SGS in the treatment of HS and K using objective measurements to confirm subjective evaluations by taking biopsies for histologic and immunohistochemical analysis. Quantitative measures used were thickness using ultrasound and perfusion using laser doppler perfusion imaging. Preliminary results showed a significant reduction of total scar thickness both in HS and in K with SGS treatment. The mean percentage change from the initial assessment of total scar thickness also showed a highly significant reduction. There was a reduction in scar perfusion, although not statistically significant, especially in HS. Biopsies were also taken from patients who at baseline and at 12 weeks had given their consent. We observed a reduction of spindle-shaped cells and an increased number of lymphocytes that strongly expressed CD11a/CD18 (LFA-1) adhesion molecules, which suggests that the SGS application induced modifications of the cell infiltrate in HS and K. It appears there is no release of silicone into the skin after silicone gel application, but this is still not definite. Silicones are synthetic polymers containing a repeating silicone-oxygen backbone and organic groups attached directly to the silicon atom. Elemental silicon is used as a starting material in the manufacture of many silicone products. The most common synthetic polymer is polydimethylsiloxane (PDMS). Depending on the length of the polymer chain and the degree of cross linking, silicone may be differentiated into different classes of commercial products. SGS is composed of gel and a HS Hypertrophic scars IL-8 Interleukin-8 K Keloids PDMS Polydimethylsiloxane SGS Silicone gel sheeting