STABI LITY TEST This study performed the sensory evaluation of time-elapsed change made over a month by date in the formulated PLO gel stored at low temperature (4°C), room temperature (25°C), and constant temperature (40°C). To determine the fl owability and separation of formulations, the cycling test was conducted to test physical stability of formulations by storing them at –15°C, 40°C, and 25°C each for 24 h. FE-SEM OBSE RVATION FE-SEM (Qua nta 3D FEG, FEI Company) was used to observe the morphological charac- teristics and properties of PLO gel. Unlike conventional electron microscopy using a thermal emission gun, FE-SEM is a fi eld emission scanning electron microscope that Table II Independent Variable Range of Preliminary Experiment Independent variables Level Low (-1) Middle (0) High (+1) A: hydrogenated lecithin (wt%) 1.0 3.0 5.0 B: PEG-400 (wt%) 15.0 20.0 25.0 C: poloxamer 407 (wt%) 15.0 20.0 25.0 Figure 2. Preparation method of PLO gel. JOURNAL OF COSMETIC SCIENCE 330

Table III Independent Variable Range for PLO Gel Optimization Experiment Run Space type Factor 1 Factor 2 Factor 3 A: hydrogenated lecithin B: PEG-400 C: poloxamer 407 (wt%) (wt%) (wt%) #2–1 Center 3.0 20.0 20.0 #2–2 IB factor 1.0 25.0 20.0 #2–3 IB factor 5.0 20.0 15.0 #2–4 IB factor 5.0 15.0 20.0 #2–5 IB factor 3.0 25.0 15.0 #2–6 IB factor 1.0 20.0 15.0 #2–7 Center 3.0 20.0 20.0 #2–8 Center 3.0 20.0 20.0 #2–9 IB factor 3.0 25.0 25.0 #2–10 IB factor 1.0 25.0 25.0 #2–11 IB factor 3.0 15.0 15.0 #2–12 IB factor 3.0 25.0 25.0 #2–13 IB factor 5.0 20.0 20.0 #2–14 Center 3.0 20.0 20.0 #2–15 IB factor 5.0 25.0 25.0 #2–16 IB factor 1.0 20.0 20.0 #2–17 Center 3.0 20.0 20.0 Figure 3. Box–Behnken design. The point at the center of the cube corresponds to the center of the Box– Behnken design, and the point at the middle of each line of the cube corresponds to the IBFact. emits electrons by generating a strong electric fi eld on the fi lament metal surface as an electron source. Compared with traditional SEM, FE-SEM has the advantage of higher resolution that provides images with a higher resolution and allows observation at high magnifi cation (up to ×100,000) using a low accelerating voltage in specimens with elec- tron beam–induced damage (27). PREPARATION AND EVALUATION OF PLURONIC LECITHIN ORGANOGELS 331