NEW RESISTANT LIPOSOME COATED WITH POLYSACCHARIDE FILM FOR COSMETIC APPLICATION 233 At stages I and II, liposomes infl ated by increasing the surfactant concentration. At the third stage, there is a drastic decrease in size due to the formation of hybrid micelles (8). By increasing the concentration of detergent, the latter integrates phospholipid mem- brane and then accelerates the destabilization of liposomes. As already described by Mady et al. (23), we confi rmed that coating of liposomes by Stearoyl Inulin decreased their de- stabilization by ionic and nonionic surfactants. Surfactants are fi rstly incorporated in the polysaccharide fi lm, which delays the arrival of surfactant to the liposome phospholipid bilayer. Moreover, due to the stearic acid and phospholipid interactions, coated mem- branes became less soluble in contact with surfactants. However, this resistance depends on the concentration and the kind of surfactant. Resistance of coated and noncoated liposomes to electrolytes. Monovalent (NaCl) and divalent (MgCl2) salts were used to evaluate the infl uence of coating process on the resistance of liposomes against the ionic strength of salts. The maximum percentages of NaCl and MgCl2, which do not destabilize coated and noncoated liposomes were summarized in Table III. Noncoated liposomes resisted up to 10% of NaCl until 15 days and 5% until 30 days. The difference is even more pro- nounced in the presence of MgCl2 where coated liposomes were stable up to 20% in comparison with noncoated liposomes, which were immediately destabilized in contact with this divalent salt. However, coated liposomes resisted surprisingly to 20% of NaCl and MgCl2 over the entire storage period. The presence of salts in the medium destabilizes the liposomes by modifying the struc- ture of phospholipid head groups (24). Furthermore, entrapment of high concentrations of MgCl2 inside liposomes suspended in low concentration water outside leads to the in- ternalization of water until complete rupture of the phospholipid membrane (25). By the hydrophobized polysaccharide coating process, liposomes became four times more resis- tant to electrolytes and then to ionic strength. The insertion and interaction of Stea- royl Inulin’s alkyl chains with phospholipid membrane guaranteed the presence of Table II Resistance Kinetics of Coated and Noncoated Liposomes to Nonionic Surfactants during 30 Days of Storage at 25°C T0 Day 1 Day 7 Day 15 Day 30 Percentage of polysorbate 20 Noncoated liposome 5.0 5.0 4.0 4.0 3.0 Coated liposome 9.0 9.0 9.0 9.0 9.0 Percentage of polyglyceryl-10-laurate Noncoated liposome 7.0 7.0 7.0 7.0 7.0 Coated liposome 9.0 9.0 9.0 9.0 9.0 Percentage of behenyl alcohol 25 EO Noncoated liposome 8.0 5.0 4.0 3.0 3.0 Coated liposome 9.0 9.0 9.0 9.0 6.0 Percentage of Triton X-100 Noncoated liposome 3.0 3.0 3.0 2.5 2.5 Coated liposome 4.0 4.0 4.0 3.5 3.0

JOURNAL OF COSMETIC SCIENCE 234 polysaccharide fi lm at the surface of liposomes, thus protecting phospholipid head groups against electrolytes. Hydrophobic interactions between alkyl chains of the hydrophobi- zed polysaccharide and phospholipids fatty acids probably stabilized the coated liposomes more than nonmodifi ed polysaccharide. MAGNESIUM CHLORIDE RELEASE FROM COATED LIPOSOMES The membrane permeability of coated liposomes was evaluated by studying the release of MgCl2 from coated liposomes to the external acrylate gel medium, reducing its viscosity. Depending on the shear rate (0–70 s-1), acrylate gel viscosity was measured at Day 0 and after 30 days at 25°C. The results are presented in Figure 3. After adding 0.24% of free MgCl2 to the acrylates gel and an equivalent amount of en- trapped MgCl2 in coated liposomes (2%), we observed a visual viscosity difference com- pared to the control acrylates gel. The gel containing free MgCl2 was completely liquid, the one containing MCCL was soft, and the control gel was hard. Figure 3. Comparison of the viscosity of acrylates gel containing coated liposome magnesium chloride (2% w/w), free magnesium chloride (0.24% w/w), and control acrylates gel at Day 0 and after 30 days of storage at 25°C. Table III Resistance Kinetics of Coated and Noncoated Liposomes to Electrolytes during 30 Days of Storage at 25°C T0 Day 1 Day 7 Day 15 Day 30 Percentage of NaCl Noncoated liposome 20.0 10.0 10.0 10.0 5.0 Coated liposome 20.0 20.0 20.0 20.0 20.0 Percentage of MgCl2 Noncoated liposome 20.0 0.0 0.0 0.0 0.0 Coated liposome 20.0 20.0 20.0 20.0 20.0