| Popis: |
Bicellar systems are lipid nanostructures formed by long- and short-chain phospholipids dispersed in aqueous solution. The morphological transitions of bicellar aggregates due to temperature, composition and time variations have been revised in this work. To this end, two bicellar systems were considered, one formed by dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) and the other formed by dipalmitoylphosphatidylcholine (DPPC) and DHPC. The relationship between the magnetic alignment, the morphology of the aggregates and the phase transition temperature (Tm) of lipids is discussed. In general terms, the non-alignable samples present rounded objects at temperature below Tm. Above this temperature, an increase in viscosity is followed by the formation of large elongated aggregates. Alignable samples presented discoidal objects below Tm. The best alignment was achieved above this temperature with large areas of lamellar stacked bilayers and some multilamellar vesicles. Bicelles represent a unique versatile structure that has different effects on the skin depending on the self-assembly adopted. The application of bicelles to the skin modifies its biophysical parameters without affecting stratum corneum (SC) lipid microstructure or promoting irritation. The penetration and growth of DPPC–DHPC bicelles inside the SC opens up new avenues for the treatment of these systems. Bicelles are an effective skin carrier owing to their size, structure, and composition. Although bicelles have no aqueous internal compartment for encapsulating drugs, their bilayered structure allows for the encapsulation of lipophilic and amphiphilic compounds. Because of their ability to increase the permeability of the SC, these structures enhance the penetration of hydrophilic components dissolved in aqueous medium. Further, the conversion of bicelles into vesicles inside the SC hinders their migration outside the tissue and allows a lipid reinforcement effect on the skin. This property could be very useful for enhancing the effects of specific compounds carried by bicelles into the SC layers. By modulating their physical and chemical characteristics, bicelles may be useful for a wide range of applications. |
