Strat-M® is a multi-layered polymer membrane designed for transdermal diffusion testing without the need to account for human skin variability, safety and storage limitations. The aim of the study is to determine the permeation kinetics of the model Active Cosmetic Ingredient (ACI) resorcinol in Strat-M®, EpiSkin® reconstructed human skin and excised human skin and to correlate these results with the characteristics of applied formulations (PBS, hydrogel, Oil/Water emulsion). While high performance liquid chromatography (HPLC) is used to assess rates of diffusion, Confocal Raman Imaging (CRI) and Normal Phase – High Performance Liquid Chromatography coupled to High Resolution Mass Spectrometry (NP-HPLC/HR-MSn) were applied to characterise the 3 models at the molecular level to reach a better understanding of formulation-skin model interactions. HPLC data from emulsions suggest permeability of Strat-MTM is ~3-fold higher compared to excised human skin but ~3-fold lower compared to EpiSkin® RHE. Concerning PBS solution and hydrogel, the permeability through Strat-M® was ~5-fold higher compared to excised human skin and ~3-fold lower compared to EpiSkin® RHE. CRI coupled to K-means clustering analysis shows that Strat-M® are composed of three layers characterised by spectral features from polyether sulfone and polyolefin, mimicking the skin’s multi-layered morphology. However, lipid analysis using NP-HPLC/HR-MSn confirm Strat-M® do not exhibit any lipids found in EpiSkin® and excised human skin, hence its barrier function to active compounds is solely due to the organisation and nature of polymers. Results obtained with resorcinol suggest Strat-MTM could be a more suitable model than reconstructed human skin for the upstream screening of hydrophilic ACI penetration.
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