Evaluating Water Permeability and Occlusion in Wound Dressings and Topical Cosmetics

By: Hongbo Zhai, MD, and Howard I. Maibach, MD, University of California

Posted: June 30, 2009, from the July 2009 issue of Cosmetics & Toiletries.

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Human skin: Human cadaver skin was obtainedd and dermatomed to a 500-micrometer thickness. Skin samples were stored in Eagle’s MEM with Earle’s balanced salt solution (BSS)e at 4ºC and used within 5 days to ensure cell viability.9-11 A total of 8 skin samples from 8 different donors were used after being examined for TEWL integrity.

Experimental Design
For each trial, four glass vials were filled with saline (0.9% NaCl) to mimic live body conditions. The skin samples were placed over vial openings, secured with latex bands, and allowed to equilibriate for 30 min, after which the baseline TEWL values were measured by evaporimeterf. The first sample was covered and banded with the occlusive film, and the second with a semi-occlusive dressing. For the third sample, 100 uL of 5% acrylates/octylacrylamide copolymer solution was spread over the skin and allowed to aerate to form a thin, presumably semi-permeable membrane upon the skin. The final skin sample was left exposed to the surrounding air, serving as a blank (untreated) control. After 30 min, TEWL values again were recorded with the evaporimeter. One trial consisted of 4 treatments, including 3 topical agents and a blank control; this trial was repeated 7 additional times for a total of 8 trials.

TEWL measurements: TEWL was measured noninvasively by lightly placing a evaporimeter on the skin or dressing without added pressure, per the standard guidelines.12-14 TEWL values were expressed as g/m2/h. During the experiment, the relative humidity (RH) and room temperature were recorded as RH = 44–55% (50 ± 3%) and temperature = 19–21°C (20±1°C), respectively.

Statistical methods: The results were statistically calculatedg and the differences were analyzed utilizing the one way repeated measure ANOVA. Statistical significance was accepted at p < 0.05.

Results
No significant results were observed between TEWL values among the wound dressings, except in the case of the purported occlusive membrane, which showed a statistically significant lower value (p < 0.05) when compared with the blank control (Figure 1).