Surface electrical capacitance as a noninvasive index of epidermal barrier in cultured skin substitutes in athymic mice

Restoration of an epidermal barrier is a definitive requirement for wound closure. To determine formation of an epidermal barrier as a function of hydration of the stratum corneum, we measured surface electrical capacitance (SEC) of the epidermis in cultured skin substitutes (CSS) in vitro and after grafting to athymic mice. CSS were prepared from human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates. On culture days 3, 7, 14, 17, and 21, SEC was measured in situ. CSS (n = 18; mean +/- SEM) showed a time-dependent decrease of SEC (picoFarads, "pF") from 4721 +/- 28 pF on day 3 to 394 +/- 117 pF on day 14, and subsequent increase to 1677 +/- 325 pF on day 21. After 14-d incubation, parallel CSS samples (n = 5) or murine autografts (n = 5) were grafted orthotopically to athymic mice. After grafting, CSS showed decreases in SEC from 910 +/- 315 pF at 2 wk to 40 +/- 10 pF at 4 wk with no significant decreases thereafter. Control values for murine autograft were 870 +/- 245 pF at 2 wk, and 87 +/- 30 pF at 4 wk. SEC values for native murine skin (n = 10) were 91 +/- 18 pF, and for native human skin (n = 10) were 32 +/- 5 pF. The data demonstrate that SEC decreases with time in culture and that healed or intact skin has approximately 10- to 100-fold lower SEC than CSS in vitro. This noninvasive technique provides a quantitative index of epidermal barrier in CSS in vitro and demonstrates the development of functional epidermal barrier during healing of wounds treated with cultured skin substitutes