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

NEW RESISTANT LIPOSOME COATED WITH POLYSACCHARIDE FILM FOR COSMETIC APPLICATION 235 Our observations were confi rmed by the viscosity values presented in Figure 3. Com- pared to the control acrylate gel, the incorporation of free and entrapped MgCl2 de- creased the acrylate gel viscosity. There was an important difference between the effects of MgCl2 whether in its entrapped or free form. 0.24% of free MgCl2 de- creased the viscosity of acrylate gel by about 41 times. However, when the same amount of MgCl2 was entrapped in coated liposomes (2%), the viscosity of acrylate gel decreased about 14 times compared to the control. These results were consider- ably different and showed that MgCl2 was partly entrapped into coated liposomes and some MgCl2 remained outside the coated liposome. Consequently, only nonen- trapped MgCl2 decreases the viscosity of acrylates gel. Figure 3 shows that viscosities of the control and acrylate gel containing free MgCl2 were stable for 30 days of storage at 25°C. Because of the strong encapsulation effi ciency of our technology, the viscosity of coated MgCl2 gel at Day 0 and Day 30 is not considerably different (Figure 3). This result re- vealed that coated liposome membrane is very resistant and does not allow the release of MgCl2 during the period of storage. Aqueous suspensions of MCCL were diluted with distilled water (1/2, 1/10) and then intro- duced into an acrylates gel to potentially induce a diffusion of MgCl2 through the coated lipo- some membrane. An equivalent amount of free MgCl2 was incorporated into acrylate gel. Figure 4 presents the viscosity of acrylate gels containing 2% of MCCL (i.e., 0.24% MgCl2), 4% of MCCL suspension diluted by half to maintain an equivalent amount of MgCl2 (i.e., 0.24% MgCl2), and 20% of MCCL suspension diluted to 1/10 (i.e., 0.24% MgCl2). Our results showed that there was no effect on the MgCl2 release after the external medium dilution of coated lipo- somes. If the membrane permeability of coated liposomes depended on the osmotic gradient, distilled water dilution would have induced the release of MgCl2 from coated liposomes. Our MgCl2 equilibrium hypothesis was then refuted because all acrylate gels containing different concentrations of entrapped MgCl2 had the same viscosity profi le. This study confi rmed that coated liposome membrane is very resistant to MgCl2 release. Liposome membranes are semi- permeable to molecules depending on different characteristics. The permeability of liposome Figure 4. Effect of dilution on magnesium chloride release from coated liposomes (Acrylates gels viscosity was measured at 25°C).