Alfons de la Maza

Bicosomes: Bicelles in dilute systems

Bicelles are discoidal phospholipid nanostructures at high lipid concentrations. Under dilute conditions, bicelles become larger and adopt a variety of morphologies. This work proposes a strategy to preserve the discoidal morphology of bicelles in environments with high water content. Bicelles were formed in concentrated conditions and subsequently encapsulated in liposomes. Later dilution of these new structures, called bicosomes, demonstrated that lipid vesicles were able to isolate and protect bicelles entrapped inside them from the medium. Characterization of systems before and after dilution by dynamic light-scattering spectroscopy and cryo-transmission electron microscopy showed that free bicelles changed in size and morphology, whereas encapsulated bicelles remained unaltered by the effect of dilution. Free and entrapped bicelles (containing the paramagnetic contrast agent gadodiamide) were injected into rat brain lateral ventricles. Coronal and sagittal visualization was performed by magnetic resonance imaging. Whereas rats injected with free bicelles did not survive the surgery, those injected with bicosomes did, and a hyperintensity effect due to gadodiamide was observed in the cerebrospinal fluid. These results indicate that bicosomes are a good means of preserving the morphology of bicelles under dilution conditions.

Liposome as dispersing agent into disperse dye formulation

Disperse dyes are very hydrophobic molecules which are usually milled in the presence of large amounts of dispersing agents (synthetic surfactants) in their commercial form. In this study the synthetic surfactants are substituted by phosphatidylcholine liposomes in the dye preparation, in order to use natural and biological surfactants. The turbidity ratio was calculated to assess the dispersion behavior of different liposome-dispersed dye preparations compared with commercial dye forms. Results indicate that liposomic preparations diminish the aggregation of dye molecules that normally occurs at high temperatures. Our findings demonstrated the potential efficacy of liposomes as natural surfactants which can be applied to disperse dye formulations to dye polyester fibers with good dye exhaustion and washing fastness. This environmentally friendly biological surfactant, phosphatidylcholine, duly structured as liposomes, can substitute high amounts of synthetic dispersing agents in disperse dye formulations.

Cosmetotextiles with Gallic Acid: Skin Reservoir Effect

The antioxidant gallic acid (GA) has been incorporated into cotton (CO) and polyamide (PA) through two different vehicles, that is, liposomes and mixed micelles, and their respective absorption/desorption processes have been studied. Moreover, in vitro percutaneous absorption tests of different cosmetotextiles have been performed to demonstrate antioxidant penetration within the layers of the skin. When GA was embedded into the cosmetotextiles, it always promoted a reservoir effect that was much more marked than that observed for polyamide. Similar penetration was observed in the textiles treated with GA in mixed micelles or liposomes in such compartments of the skin as the stratum corneum, epidermis, and even the dermis. GA was detected in receptor fluid only when CO was treated with MM. This methodology may be useful in verifying how encapsulated substances incorporated into textile materials penetrate human skin. Indeed, such materials can be considered strategic delivery systems that release a given active compound into the skin at specific doses.

Characterization of new DOPC/DHPC platform for dermal applications

Systems formed by mixtures of the phospholipids dioleoylphosphatidylcholine (DOPC) and dihexanoylphosphatidylcholine (DHPC) were characterized by use of differential scanning calorimetry, small angle X-ray scattering and two electron-microscopy techniques, freeze fracture electron microscopy and cryogenic transmission electron microscopy. These techniques allowed for the determination of the size, morphology, structural topology, self-assembly and thermotropic behavior of the nanostructures present in the mixtures. The interaction between the two phospholipids provides curvatures, irregularities and the increase of thickness and flexibility in the membrane. These effects led to the formation of different aggregates with a differential distribution of both phospholipids. The effect of these systems on the skin in vivo was evaluated by measurement of the biophysical skin parameters. Our results show that the DOPC/DHPC application induces a decrease in the permeability and in the hydration of the tissue. These effects in vivo are related to different microstructural changes promoted by these systems in the skin in vitro, published in a recent work. The fundamental biophysical analyses of DOPC/DHPC systems contribute to our understanding of the mechanisms that govern their interaction with the skin.

CHAPTER 8:Bicellar Systems: Characterization and Skin Applications

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.

Gallic acid vehiculized through liposomes or mixed micelles in biofunctional textiles

Liposomes and mixed micelles were used to vehiculize gallic acid, as antioxidant, when applied to different textiles designed to be in contact with the skin as biofunctional textiles. Foulard and bath exhaustion processes were assayed without the use of a binder. Liposomes with the antioxidant encapsulated were applied to cotton, polyamide, polyester, acrylic, and wool, using bath exhaustion and the pad-dry process. Higher absorption was obtained with bath exhaustion than with the pad-dry process for all fabrics. Liposome application to the different textiles showed an adequate substantivity for most fibers. However, the high desorption of most synthetic acrylic and polyester fibers confirmed the preferential application of cotton and polyamide as cosmetic biofunctional textiles. Moreover, this study showed that polyamide always presented high substantivity for the two phospholipid structures and also for the antioxidant.