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Temporal imaging chamber (TIC) for en face imaging of epidermal absorption in vitro

Two-photon and confocal microscopy can be used to study the absorption of fluorescent compounds in tissue e.g. for evaluation of topical drug delivery systems. Images of drug distribution at different depth in the skin with relatively high spatial resolution are obtained. However, presented results are often static images from one single time point after topical application. We present an online diffusion cell with optical access allowing for temporal imaging of skin penetration and measurement of percutaneous absorption in vitro. The temporal imaging cell (TIC) is adopted for both two-photon and confocal microscopy. In this study the TIC has been used to visualize the change in absorption of Rhodamine B with time at different depth in human epidermis using two-photon microscopy. Imaging showing the penetration of Rhodamine B with time are presented together with transepidermal fluxes measured in TIC's and in traditional diffusion cells. In conclusion we have shown that the TIC is a promising tool for temporal studies of the absorption of fluorescent compounds in tissue. E.g. sample preparation is held to a minimum prior to imaging, improved detection and resolution in viable epidermis is achieved by imaging from the dorsal side of skin and the possibility to simultaneously analyze the acceptor liquid increases the information available from each experiment.