Molecules of lyotropic liquid crystal forming surfactants at certain concentrations in solution spontaneously associate and organize into structures or mesophases, such as lamellar, hexagonal, and cubic lyotropic liquid crystal. These systems are studied in the field of pharmacy as delivery systems for various applications, including dermal and subcutaneous. Important information regarding lyotropic liquid crystals’ microstructure can be obtained through differential scanning calorimetry, a thermal analysis technique that provides insights into the state of water, a liquid crystals’ component, through the study of phase transitions. Water, located near the polar heads of surfactants in the liquid crystal system, exhibits different thermal properties due to interactions that reduce its degrees of freedom compared to water that is more distant from the polar heads.
As part of the Master's thesis, we first evaluated formulations for dermal application based on linseed or hemp oil, in which the presence of lamellar phases was previously confirmed during development phase with polarizing microscopy. Betamethasone dipropionate as active ingredient was incorporated into the formulations and its impact on the microstructure was also studied. Based on obtained results, within formulations with 30 % water, the water molecules are located near the polar heads of surfactants are bound, while in formulations with more that 50 % water, the polar heads are saturated with water molecules, and free water is also present in the system. Comparing individual formulations without and with the incorporated betamethasone dipropionate, we concluded that in formulations with 30 % water, the active pharmaceutical ingredient is incorporated between the lamellae, while in formulations with 80 % water, it is incorporated into oil droplets present separately in addition to lamellar phases.
Furthermore, we evaluated precursor formulations for subcutaneous application based on glycerol monooleate or glycerol monolinoleate and gels that are formed in situ after injection of the precursor formulation into the subcutaneous tissue. During development, the presence of cubic and hexagonal phases of liquid crystals was confirmed using polarizing microscopy for gels formed in situ. Based on obtained results, we found that in gels with 50 % lipid phase in the precursor formulation, most of the water is located near the polar heads of the surfactants and is bound, while in gels with 20 % lipid phase in the precursor formulation, the polar heads of the surfactants are already saturated with water molecules and free water is present in the system.
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