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

DSC MEASUREM ENT Differential scanning calorimetry (DSC 214 Polyma, Netzsch, Germany) was used in thermal analysis of formulated PLO gel. Temperatures ranged between –6 ~ 90°C in the fi rst heating, 90 ~ -60°C in the fi rst cooling, and 60 ~ 90°C in the second heating cycles at a heating rate of 10°C/min. The temperature ranges were selected to assess the change in the physical properties of PLO gel by temperature, and measurements on nitrogen were carried out. RHEOLOGY MEASUREMEN T To assess rheologic al properties including viscosity and elasticity in PLO gel formula- tions, viscoelasticity was measured using a rheometer (Rheolaser Master, Formulaction, Toulouse, France). In general, scatterers (particles, droplets, fi bers, etc.) are constantly in motion because of Brownian motion in samples with viscoelastic properties. This constant motion of scatterers results in deformation of speckle image by time. The speed of scatterer movement varies by viscoelastic properties and also affects the deformation speed of speckle image. Therefore, the rheological properties of the sample including viscoelasticity can be assessed by measuring the deformation speed of speckle image. The Rheolaser Master uses diffusing-wave spectroscopy (DWS), which is an optical technique derived from dynamic light scattering (DLS). The DWS method is based on microrheology (28). The measurement of rheological properties was performed by converting the change in the mean square displacement (MSD) over a period of time into numerical values. Measurement was performed at room temperature (25°C) for 3 h. IN VITRO SKIN PERMEA TION TEST The transdermal Fran z diffusion cell system (FDC-6T, Logan, Somerset, NJ) was used to determine the skin permeation effi ciency of the formulated PLO gel. An artifi cial mem- brane (Strat-M membrane) was set in the diffusion cell array system, and in vitro percuta- neous absorption test was carried out by applying 400 μL of test solution in the donor and 50% ethanol solution in the receptor at 32 ± 1°C. The receptor fl uid in the receptor compartment was collected at 2, 4, and 8 h after applying the test solution, and skin penetrant in the donor solution and all membranes was collected 8 h after applying the test solution. The collected solutions were analyzed with the HPLC system (Alliance HPLC, Waters, Santa Clara, CA) under the conditions presented in Table IV. Table IV HPLC Analysis Condition Instrument Conditions Column C18 4.6 mm × 250 mm, 5.0 μm Column temp. 40°C Mobile phase Methanol: 0.01% Trifl uoreoacetic acid in Water (5:95) Detector PDA Detector (261 nm) Flow rate 1.0 mL/min Injection volume 10 μL JOURNAL OF COSMETIC SCIENCE 332