390 JOURNAL OF COSMETIC SCIENCE lamellar vesicles, as observed under optical microscope. The mean diameters of MLV liposomes containing OMC determined by PSA were 2.21 ± 0.06 µm (n = 3). The SUV liposomes were negatively stained and photographed with an electron micro­ scope to characterize the morphology and size distribution of the liposomes (Figure 1). These liposomes were SUV with a size of 62 ± 21 nm. In this study, liposomes with high encapsulation efficiency were prepared. Encapsulation efficiencies of MLV and SUV liposomes containing OMC were 89.66% ± 2.08 and 89.7% ± 0.7 (n = 3), respectively. Statistical analysis showed that encapsulation effi­ ciency of OMC is independent of liposome size and that there were no significant differences in the encapsulation efficiency of MLV and SUV liposomes (p 0.05 ). These liposomes exhibited no changes in encapsulation efficiency when stored at room tem­ perature for over three months. DETERMINATION OF THE SPF OF THE HOMOSALATE REFERENCE, COLIPA REFERENCE, O/W EMULSION, AND LIPOSOMES CONTAINING OMC BY IN VIVO METHOD The homosalate reference product and the COUP A high reference product were both used to validate the results of SPF determination. The SPF of the references and samples were determined by the Australian standard in vivo method. According to this method, the SPF of the homosalate standard product was calculated as 4.35 ± 0.64, and there were no significant differences between our in vivo study value (4.35 ± 0.64) and the claimed SPF (4.47 ± 1.279), with p 0.05 (Table I). The data obtained from our study show that the differences between the SPF obtained from our in vivo results (15 .2 ± 3.4) and the published SPF for COLIPA high reference (15.3 ± 2.1) were not significant. The SPF of the liposomes containing OMC was a little bit greater than that of the OMC lotion at the same concentration of OMC however, the difference was not quite signif­ icant. Figure 1. Transmission electron micrograph of SUV liposomes containing OMC (100,000x).

Table I The SPF Values of the Homosalate Reference, COLIPA Reference, OMC Lotion, and OMC Liposomes Determined by In Vivo Method in Ten Subjects with Different Skin Types Sunscreen Sl S2 S3 S4 S5 S6 S7 S8 S9 Sl0 SPF (mean ± SD) Homosalate reference 4 4.46 4.56 4.90 4 4.92 3.62 4.44 5.63 4.05 4.35 ± 0.64 COUP A reference 12.4 15.5 19.4 14.5 17.1 12.4 15.5 15.5 12.4 19.4 15.2 ± 3.4 OMC lotion 14.2 15.5 12.4 12.3 15.5 17.1 12.3 12.4 15.5 12.3 13.95 ± 1.83 OMC liposomes 17.1 19.3 19.4 12.4 15.5 14.5 19.4 17.1 14.5 15.5 16.57 ± 1.40 'ij rn � n C '"""1 z rn 0 C C/) b:l C/) 0 � 'ij '"""1 0 0 1-rj 0 � n \..)J \0 .......