EMULGEL FORMULATION AND IN VITRO AND IN VIVO ASSESSMENT 5 travel the distance of 30.6 cm and to separate away from the lower slide under the infl u- ence of the weight was calculated (22). Spreadabi lity was calculated by using the following formula: S , l Mq t where S is the spreadability, m weight tied to the upper slide (150 g), l length of the glass (30.6 cm), t time in seconds. In addition, the viscosity of the emulgel was measured at varying speeds, from 0.5 to 50 rpm. Assessment of the Sun Protection Factor (SPF). Sunscreen is used to minimize the effect of ultraviolet radiation on the skin because the ultraviolet light is one of the major causes of skin cancer (23). Sunscreens are classifi ed according to their SPF value. The SPF value of our formulation was assessed according to the Mansur method as reported in the following text. Stock solu tion preparation. A stock so lution of 50 μg/mL concentration was prepared by weighing 5 mg of LG emulgel in an elementary fl ask, and then ethanol (99.9%) was added to LG emulgel until the volume reached 100 mL. Absorbance determination. A spectroph otometer (Jenway, UK) was used to measure the absorbance of different samples between 290 and 320 nm (Table III). The SPF could be calculated using the Mansur equation (24). Ȝ Ȝ Ȝ q q qabs œEF 320 290 SPF Spectrophotometric CF , I where CF i s the correction factor, and it is equal to 10 EE (λ) denotes erythemal effect spectrum I (λ) is the solar intensity spectrum and Abs is the absorbance of a sunscreen product. The values of EE (λ) × I (λ) are constants. It is determined by (25). Cutometer. T he Cutomet er® skin elasticity meter (SEM) 575 (COURAGE+KHAZAKA electronic GmbH, Köln, Germany) (Figure 1A), which is the successor of the Cutometer SEM 474, is an independent device that includes two basic parts. The main unit is a metal housing containing a vacuum pump with a pressure sensor and microelectronics. The load of the vac- uum (negative air pressure), the rate of its increase or decrease, the duration of suction (on time) and relaxation (off time), and the number of measuring cycles during one measurement can be defi ned through Cutometer software. The resolution of applied pressure is equal to 1 mbar. The measuring probe is a handheld probe containing the suction head, optical measur- ing system, and microelectronics. The suction head is centered in the probe and has a standard Table III Normalized Product Function Used in the Calculation of SPF Wavelength (λ nm) EF (λ) × I (λ) 290 0.0150 295 0.0817 300 0.2874 305 0.3278 310 0.1864 315 0.0839 320 0.0180 Total 1

JOURNAL OF COSMETIC SCIENCE 6 circular aperture of 2-mm diameter (test area of about 3 mm). Optional probes with apertures of 4, 6, and 8 mm are available on request. The measuring system inside the probe head is noncontact and consists of a light source (light-emitting diode) and a light recipient, as well as two opposing glass prisms, which project the light from the emitter to the recipient. The changes of the infrared light beam intensity during measurement are converted into millime- ters (from 0 to 3.0 mm) and calculated with a resolution equal to 2 μm. The measuring probe is connected to the main unit through an air tube and an electric cable. During measurement, it is held perpendicularly to the skin surface under constant pressure ensured (provided) by an elastic spring. The calibration data are stored in the memory of each probe, which allows fast and easy exchange of probes with different apertures. The Cutometer MPA 580 (COURAGE+KHAZAKA electronic GmbH) (Figure 1B), that is currently available, com- bines the vacuum box for the Cutometer with a built-in Sebumeter (SM) 815 and a modular multi-probe adapter system which makes possible to connect up to four additional measuring probes as well as an ambient condition sensor. MEASURING TECHNIQUE S There are two measu ring techniques available: 1. In the strain–ti m e mode, the deformation of the skin (in millimeters) is showed as a function of time (in seconds). This mode is mostly used in research studies. Figure 1. (A) Cutometer SEM 575. (B) Cutometer MPA 580.