Corneocyte quantification by NIR densitometry and UV/Vis spectroscopy for human and porcine skin and the role of skin cleaning procedures.

Optical methods of corneocyte quantification during tape stripping experiments on the skin are useful tools for the rapid evaluation of the skin penetration potential of dermally applied substances. However, a comparative investigation of the different methods proposed for this task, namely NIR densitometry and UV/Vis spectroscopy, is still missing. Thus, the aim of the present work was to employ these two techniques in comparative tape stripping experiments both in vivo on human forearm skin and in vitro on porcine ear skin. Standard tape stripping experiments were performed in the absence and presence of a marketed formulation containing flufenamic acid as a model drug. In the context of these methodological investigations, different methods of skin cleaning prior to the tape stripping procedure were evaluated to identify the most appropriate working protocol among the approaches proposed in the respective literature. The results showed that the investigated methods of NIR densitometry and UV/Vis spectroscopy deliver highly comparable results. Both optical methods are suitable to determine the skin penetration profiles of active substances during in vivo and in vitro tape stripping, especially if a simple working protocol without any cleaning procedures is maintained.