JOURNAL OF COSMETIC SCIENCE 232 STABILITY OF LIPOSOMES Resistance of coated and noncoated liposomes to surfactants. The physicochemical stability of empty coated and noncoated liposomes was evaluated in the presence of ionic (SDS, SLES) and nonionic surfactants (Triton X-100, Polysorbate 20, polyglyceryl-10-laurate, Behe- nyl alcohol ethoxylate). The maximum percentages of ionic surfactants which do not destabilize empty coated and noncoated liposomes are shown in Table I. The shape of liposomes was observed after each period of time (Days 1, 7, 15, and 30) by optical microscope (×1000) at different ionic surfactant concentrations (1%–10%). Coated liposomes resisted up to 3% of both ionic surfactants until 30 days of storage in the presence of SDS and SLES. How- ever, noncoated liposomes are less resistant and remained stable at 1% and 2% of SDS and SLES during the period of storage, respectively. These observations allowed us to conclude that the coating process increases the stability of liposomes against ionic surfactants. The effect of different nonionic surfactant concentration (1%–10%) on the stability and shape of empty coated and noncoated liposomes was summarized in Table II. Firstly, coated and noncoated liposomes are more resistant to nonionic surfactants than to ionic ones. Whatever the kind of nonionic surfactant, the coating process improved the stability of liposomes. Our results showed that coated liposomes remained stable with good integrity in the presence of 9% of polysorbate 20 and 9% of polyglyceryl- 10-laurate for 30 days. Coated liposomes resisted up to 9% of behenyl alcohol 25 EO for 15 days but only up to 6% after 30 days. However, Triton X-100 is the most solu- bilizable nonionic surfactant as coated liposomes were stable until 30 days of storage in the presence of 3% of Triton X-100. Noncoated liposomes are more resistant to behenyl alcohol 25 EO and polyglyceryl-10-laurate than to polysorbate 20 and Triton X-100. Surfactants are widely used for the solubilization of phospholipid membrane. Mady et al. (23) have reported that the solubilization process is divided into three stages. (i) Stage I: corresponds to the insertion of surfactants into the bilayer membrane. (ii) Stage II: reached when the phospholipid membrane is saturated with surfactants, and followed by the formation of micelles. (iii) Stage III: Mixed lipid-surfactant micelles enriched in surfactant. Table I Resistance Kinetics of Coated and Noncoated Liposomes to Ionic Surfactants during 30 Days of Storage at 25°C T0 Day 1 Day 7 Day 15 Day 30 Percentage of SDS Noncoated liposome 1.0 1.0 1.0 1.0 1.0 Coated liposome 4.0 4.0 4.0 4.0 3.0 Percentage of SLES Noncoated liposome 2.0 2.0 2.0 2.0 2.0 Coated liposome 4.0 4.0 4.0 3.0 3.0 SDS: Sodium dodecyl sulfate, SLES: Sodium lauryl ether sulfate.

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