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Without emollient (control), the liquid from the vial permeates the collagen skin-mimic film and the pH increases rapidly like the blue curve in Figure 10. The more emollient applied, the slower the pH increases at the electrode side. The kinetic results prove that emollient acts as a barrier and slows the diffusion rate of a high pH liquid into and through the collagen skin-mimic film skin analog. The change in pH as a function of time in these experiments was done in triplicate (or duplicate in one case) and the average results were plotted. The data are shown in Tables 4 and 5. The overall average standard deviation for replicate measurements was 0.65 pH units. It is believed that much of the variability comes from location-dependent variation of the collagen skin-mimic film material.

Fig. 10. Collagen skin-mimic film diffusion test: rate of pH change slows with increasing emollient. This demonstrates that skin pH could be measured effectively.

Table 4. pH data as a function of time with no emollient applied to the collagen skin-mimic film

Table 5. pH data as a function of time with emollient applied to the collagen skin-mimic film