006 Reduction of Scarring by Silicone in the Rabbit Ear Model

Abstract

Hypertrophic scars can be reduced by application of silicone dressing; however, the detailed mechanism of silicone action is still unknown. It is known that silicone gel sheets cause a hydration of the epidermal layer of the skin. An in vitro coculture experiment has shown that hydration of keratinocytes has a suppressive effect on the metabolism of the underlying fibroblasts resulting in reduced collagen deposition. We tested the hypothesis that silicone gel sheeting in vivo has a beneficial effect on scar reduction by a reduction in keratinocyte stimulation, with a resulting reduction in dermal thickness. Silicone adhesive gel sheets were applied to scars in our rabbit ear model of hypertrophic scarring 14 days post wounding for a total of 14 days. Scarring was measured in this model by the Scar Elevation Index (SEI), a ratio of the scar height over normal skin, and the Epidermal Thickness Index (ETI), a ratio of the epidermal height of the scar over normal epidermis. Ultrastructural changes were investigated using electron microscopy (EM). SEIs were significantly reduced after only 2-week applications of silicone gel sheets versus untreated scars (1.18 ± 0.05 vs. 1.45 ± 0.09, respectively; P < 0.05)– corresponding to a 48.8% reduction of scar hypertrophy. The epidermal layer in scars was in general thicker than in unwounded skin. However, ETIs of untreated scars increased by 103% versus 71% after silicone gel treatment – corresponding to a significant reduction of epidermal thickness by 24.4%. EM showed a basal layer in untreated scars that was very different than normal skin with many vacuoles at the basement membrane level, while silicone gel-treated scars had a basal cell layer which resembled unwounded epidermis. Our findings demonstrate that 2 weeks of silicone gel application at a very early onset of scarring reduces dermal thickness which appears to be due to a reduction in keratinocyte stimulation. These findings are consistent with our coculture results.