Lyotropic liquid crystals (LCCs) represent a modern approach in the development of dermal delivery systems for the treatment of atopic dermatitis (AD), primarily due to their unique microstructure showing high similarity to the lipids of the stratum corneum. Their use promises enhanced penetration of active ingredients and a positive impact on the repair of the skin barrier. In this master’s thesis, we aimed to evaluate the effect of various LLC formulations on skin barrier function in vivo, focusing on key indicators: transepidermal water loss (TEWL), skin hydration, melanin index (MI), and erythema index (EI). We prepared eight different LLC systems that varied in the type of oil phase, surfactant used, and water phase content. The study included 12 volunteers, for whom we compared baseline values with measurements taken after single (eight hours) and prolonged application (14 days) of each formulation. The results showed that formulations with a lower water content significantly reduced TEWL already 8 hours after the first application, indicating an immediate positive effect on the skin barrier function. After 14 days of use, similar effects were observed with formulations containing higher water content, suggesting a more gradual but sustained action. The greatest reduction in TEWL was noted in formulations rich in lipids, confirming the importance of selecting a natural oil phase with a high content of essential fatty acids. Hydration measurements revealed that formulations with higher water content significantly improved skin moisture after 14 days of use, whereas single application did not lead to statistically significant changes. The moisturizing effect was thus positively correlated with the proportion of the water phase in the formulation. The EI mostly decreased or remained unchanged following the application of all formulations, indicating a favorable anti-inflammatory profile. However, the most notable reduction in EI was again observed in formulations with lower water content, consistent with improved barrier function and the presence of anti-inflammatory ingredients in these formulations. As anticipated, the MI did not change significantly during the study given that the ingredients used do not affect melanogenesis. The results demonstrated that the selected formulations have a positive effect on skin barrier function, as most systems contributed to reduced TEWL and improved skin hydration, without causing an increase in erythema or changes in pigmentation. It was found that the composition of the LLCs, particularly the type of oil phase and the proportion of the aqueous phase, significantly influences their dermal effect. The study was conducted on healthy volunteers, which limits direct comparison to AD patients at this time, nevertheless the study confirms the potential of LLCs as safe and effective dermal formulations for atopic skin.
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