Lamellar liquid crystals have been due to their unique structure and properties used as dermal delivery system for lipophilic, hydrophilic or amphiphilic compounds. Ascorbyl palmitate is a well-known antioxidant that is widely used in pharmacy and cosmetics. It is considered as a very unstable amphiphilic compound, which degrades under the influence of light, oxygen, temperature, humidity as well as in suboptimal formulations. In the first part of the thesis we evaluated the stability of ascorbyl palmitate incorporated in eight different systems of liquid crystals (TK 1-TK 8), with a constant ratio of lipophilic compounds and surfactants and with increasing water content as hydrophilic compound. Before the stability study the present HPLC method for ascorbyl palmitate determination was upgraded. Namely, the method was optimized and validated by evaluating the selectivity, repeatability, accuracy, linearity and stability. Further, as a part of the 56-day study we showed that the stability of ascorbyl palmitate was decreasing with increased water content in liquid crystals. Stability of ascorbyl palmitate was better in liquid crystals with lower water content (TK 1-TK 5) compared to liquid crystals with higher water content (TK 6-TK 8). After 28 days of storage at 40 °C and 75 % relative humidity TK 1 (20 % (w/w) of water content) was the most stable system and TK 8 (55 % (w/w) of water content) was considered to be the least stable system. Based on calculated reaction rate constants and R2 we determined that kinetics of chemical reactions of ascorbyl palmitate follows 1. order. Values of the reaction rate constants showed a decreasing stability from TK 1 (0,023 d-1) to TK 8 (0,043 d-1) as the constant increased with increasing water content.
In the second part of the thesis we evaluated in vitro release of ascorbyl palmitate from eight systems of liquid crystals. The study was performed on an artificial membrane using Franz diffusion cells. We assumed that the release would depend on the internal structure and viscosity of the systems, which varies with the proportion of water. Therefore, a faster release and to a greater extent was confirmed for systems TK 1-TK 4, which contained smaller amounts of free water in the interlamellar spacing and thus shorter distances between lamellaes, compared to systems TK 5-TK 8, where due to increasing water content the distances between lamellaes are increasing in the presence of micelles.
We concluded that liquid crystals can be used as delivery system for sustained release and that they show a great potential as dermal delivery system.