TEWL measurements as a routine method for evaluating the integrity of epidermis sheets in static Franz type diffusion cells in vitro. Limitations shown by transport data testing

The suitability of transepidermal water loss (TEWL) measurements in vitro as a barrier integrity test for human heat separated epidermis (HSE) was investigated. A model system consisting of a Teflon membrane mounted in Franz diffusion cells (FDC) filled with phosphate buffer saline (PBS) was set up. The membrane was used intact and punctured with a needle (up to five holes). After each puncturing the TEWL was measured. Only the TEWL of intact and punctured membrane differed significantly regardless of the number of holes. From three donators intact human HSE and punctured HSE were compared and no significant difference of the TEWL was found. Permeation experiments with flufenamic acid (FFA) showed a significantly higher diffusion rate through punctured HSE. TEWL and drug permeation were compared for skin stripped three, seven and 15 times prior to heat separation to an intact control group. Only the TEWL values of intact HSE and HSE stripped 15 times differed significantly. However, seven and 15 times stripping resulted in significantly higher diffusion rate. In conclusion, TEWL measurements can detect severe damage of the stratum corneum (SC) but not small changes, which nevertheless may already influence drug diffusion. Therefore, TEWL measurements appears to be of limited use as a barrier integrity test for human HSE in in vitro test systems.