Effect of cryopreservation conditions on transdermal permeation of skin by two-dimensional Raman spectroscopic...

The permeability of active ingredients through the skin is markedly influenced by cryopreservation duration and storage temperature. In this study, two-dimensional Raman imaging was developed to visualize the distribution of target substances in skin tissues. Combined with the non-negative least squares algorithm, multiple linear regression was adopted to calculate the relative concentration coefficients of analytes within the skin. Ferulic acid and betaine were chosen as model compounds to explore the impacts of storage conditions on skin permeation. The results revealed that skin permeability declined progressively with prolonged cryopreservation time. Moreover, skin samples stored at -80 °C exhibited a milder reduction in permeation efficiency than those preserved at -20 °C. The results from high-performance liquid chromatography (HPLC) also confirmed that the permeation efficiency of the skin decreased with the extension of skin storage duration. This finding was consistent with that obtained via Raman imaging, demonstrating that Raman imaging serves as a reliable technique for semi-quantitative analysis. Fourier transform infrared spectroscopy (FTIR) was further utilized to characterize structural alterations in the stratum corneum under different preservation protocols. Mechanistically, the reduced skin permeability was closely correlated with structural variations of lipids in the stratum corneum. This work established a novel technical strategy for skin permeation research and offers practical guidance for skin preservation.