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 mo und closure, To determine formation of an epidermal barrier as a funct ion of hydration of the stratum corneum, we measured surface electrica l 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-glycosaminogl ycan substrates, On culture days 3, 7, 14, 17, and 21, SEC was measure d 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 +/- 1 17 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 autogra fts (n = 5) were grafted orthotopically to athymic mice. After graftin g, CSS showed decreases in SEC from 910 +/- 315 pF at 2 wk to 40 +/- 1 0 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, an d 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 n oninvasive technique provides a quantitative index of epidermal barrie r in CSS in vitro and demonstrates the development of functional epide rmal barrier during healing of wounds treated with cultured skin subst itutes.