JOURNAL OF COSMETIC SCIENCE 226 In cosmetics and toiletries, electrolytes have an important role on the sensorial properties of fi nal products because they infl uence the gel formation. They are largely used in sham- poo, deodorants, and as water in oil emulsion stabilizers. Also, several studies reported the benefi cial effect of some salts on human cutaneous barrier functions (5,6) and on bio- logical mechanisms (7). Moreover, surfactants are widely used in personal care products for emulsion stabilization and for their several properties such as detergency, solubilization, conditioning, thicken- ing, and emolliency (8). Surfactants are also used in toiletries formulations as rheology controllers to modify the viscoelastic properties and thus the sensorial characteristics of the fi nal product (9). Deo et al. (10) have reported that liposomes made of phosphatidyl- choline and phosphatidic acid are very sensitive to surfactants. In the presence of dodecyl sulfonate, the size of liposomes increased until complete solubilization. It has been reported from several studies that the stability of liposomes can be enhanced by modifi cation of their surfaces using a coating process with natural polysaccharides (i.e., mannan, pullulan, amylopectin, dextran, chitosan) (11). However, the adsorption of these polysaccharides to the liposome membrane seemed to be thermodynamically unstable (12). The use of chemically modifi ed polysaccharides for coating liposomes may avoid this stability problem (13–15). Good stability could be obtained by coating the outermost surface of liposomes with derivatives of polysaccharides (16–18). Fatty acids are chemi- cally grafted to natural polysaccharides to make them amphiphilic. The hydrophobic al- kyl chains of modifi ed polysaccharides were then anchored into the bilayer membrane of liposomes. The fi rst part of our study was the physicochemical characterization of modifi ed polysac- charide coated liposomes compared to classical noncoated liposomes. Then, we evaluated the resistance of coated liposomes versus noncoated ones to different concentrations of ionic/ nonionic surfactants and electrolytes. In order to evaluate the delivery property of coated liposomes, magnesium chloride (MgCl2), a divalent salt, was chosen as the bioactive mole- cule which is implicated in P-glycoprotein (P-gp) transporter activity. Natural MgCl2 has interesting cosmetic properties as it plays an important role in the expulsion of wastes out of cells and then avoids the accumulation of reactive oxygen species. Detoxifi cation of cells was regulated by P-gp transporter it is a magnesium-dependent transmembrane pump. In this way, 12% of MgCl2 was entrapped in coated liposomes. These coated liposomes loaded with MgCl2, called magnesium chloride-coated liposomes (MCCL), were physico- chemically characterized. The MgCl2 release from MCCL was then measured in an acry- late gel formula whose viscosity is known to be very sensitive to divalent ions. The delivery property of this resistant liposome was evaluated by an ex vivo study on human skin explants. MATERIALS AND METHODS MATERIALS Two soybean lecithins (Emulmetik™ 930 and Emulmetik™ 900) distributed by Lucas Meyer Cosmetics were used for the preparation of liposomes. They are composed of about 92% and 45% of phosphatidylcholine, respectively.

NEW RESISTANT LIPOSOME COATED WITH POLYSACCHARIDE FILM FOR COSMETIC APPLICATION 227 1,3-propanediol was purchased from DuPont Tate & Lyle (Loudon, TN). Stearoyl Inulin was obtained from Miyoshi (Saitama, Japan), and α-tocopherol from VitaeCaps (Talavera de la Reina, Spain). Dermosoft® 1388 and polyglyceryl-10-laurate were supplied by Dr. Straetmans (Hamburg, Germany). Natural MgCl2 was purchased from Celnat (Saint-Germain Laprade, France) and acry- lates/C10-30 alkyl acrylate cross-polymer from Lubrizol (Wickliffe, OH). Sodium lauryl ether sulfate (SLES) was purchased from Cognis (Monheim, Germany) and Polysorbate 20 was obtained from Kolb (Hedingen, Switzerland). Behenylalcoholethoxyl- ate, Triton X-100, and sodium chloride (99%) were provided by Prolabo (Darmstadt, Germany). Phosphate-buffered solution (PBS), ascorbic acid, bicinchoninic acid, glutathi- one, and sodium dodecyl sulfate (SDS) (≥99%) were purchased from Sigma (Saint-Quentin Fallavier, France). Pgp-Glo™ Assay Systems were purchased from Promega (Charbon- nieres, France). Parabens and phenoxyethanol were provided from Jan Dekker (Langenfeld, Germany). Xanthan gum and sodium hydroxide were purchased from Cargill (Hamburg, Germany) and Le Comptoir Français Interchimie (Compans, France), respectively. LIPOSOME PREPARATION Natural polysaccharides are chemically hydrophobized by grafting stearic acid chains via an ester bond. Coated liposomes were prepared by dissolving phospholipids in 1,3- propanediol (7:20 w/w) at 70°C. Then, polysaccharide-fatty acid complex (Stearoyl Inulin) was incorporated at 75°–80°C to the homogenous mixture. After adding 0.1% of α-tocopherol to the previous mixture, the aqueous phase was vigorously homogenized with lipid phase using a rotor stator for 20 min at 1500 rpm. Finally, the coated liposome suspension was homogenized using Turrax for 5 min at 3000 rpm to reduce the polydispersity of vesicles. At the end of the process, 0.5% of Dermosoft® 1388 was added as antimicrobial system. Noncoated or classical liposomes were prepared under the same conditions (process and composition) without adding polysaccharide-fatty acid complex. MAGNESIUM CHLORIDE ENTRAPMENT Coated and noncoated liposomes entrapped MgCl2 were prepared by adding 12% (w/w) of MgCl2 into the aqueous phases before their homogenization with the lipid phases. LIPOSOME CHARACTERIZATION Structural characterization. Optical microscope and freeze-fracture electron microscopy were used to determine the morphology of liposomes. Vesicles were observed under an optical microscope (Nikon Eclipse 50i from Nikon, Kanagawa, Japan) immediately after their preparation. Coated and noncoated lipo- somes were deposited between two glass lamellas and observed using a phase contrast