For fluorescence microscopical observation of transdermal delivery of dextran molecules and NPs into the skin, the excised skin samples were cryosectioned to minimize quenching the fluorescence in paraffin processing. Briefly, skin tissues were embedded in optimum cutting temperature (Sakura Finetek) first. Then, they were sectioned at 10 μm using Leica CM3050 S Cryostat and stained with H&E under standard protocols. The H&E-stained cryosections can be found in Figs. 1E , 2G , and 4B and figs. S2C, S11D, S14A, S17E, and S18E.
To look for microscopic histological changes, samples were sectioned using paraffin-embedded tissue. Briefly, skin tissues were transferred into 70% ethanol after fixation and processed for paraffin embedding using an automated tissue processor (Leica Tissue Processor HistoCore Pearl). Paraffin-processed tissues were immediately embedded into paraffin blocks and sectioned at 5 μm. Hematoxylin (catalog no. 3801570, Leica) and eosin (catalog no. 3801615, Leica) histological stain was performed and mounted using Organo/Limonene mount (catalog no. O-8015, Sigma-Aldrich). Slides were allowed to dry overnight and imaged using an Axioscan.Z1 slide scanner (Zeiss). The H&E-stained paraffin sections can be found inFig. 5 and figs. S12A and S13A.
To look for microscopic histological changes, samples were sectioned using paraffin-embedded tissue. Briefly, skin tissues were transferred into 70% ethanol after fixation and processed for paraffin embedding using an automated tissue processor (Leica Tissue Processor HistoCore Pearl). Paraffin-processed tissues were immediately embedded into paraffin blocks and sectioned at 5 μm. Hematoxylin (catalog no. 3801570, Leica) and eosin (catalog no. 3801615, Leica) histological stain was performed and mounted using Organo/Limonene mount (catalog no. O-8015, Sigma-Aldrich). Slides were allowed to dry overnight and imaged using an Axioscan.Z1 slide scanner (Zeiss). The H&E-stained paraffin sections can be found in