HYDROGELS AND ORGANOGELS AS VEHICLES 629 Asiaticoside has wound-healing activity, promotes fi broblast proliferation, and increases the level of enzymatic and non-enzymatic antioxidants. Some of the phenolic compounds in the extract of Centella asiatica display the same benefi cial activity as α-tocopherol. The crude extract of Centella asiatica has been shown to be non-toxic in normal human lympho- cytes and has reduced the genotoxic effects of methyl methanesulphonate and cyclophos- phamide in cultured human lymphocytes (19,20). Pluronic F-127® = Lutrol F-127 = Poloxamer 407 INCI contains water 0.01%, oxypropylene-oxyethylene 71.5%–74.9%, and propylene oxide 1ppm. Poloxamers are synthetic block copolymers of hydrophilic ethylene oxide chains and hydrophobic propylene oxide chains, with the general formula of HO–[C2 H4 O]a –[C3 H6 O]b –[C2 H4 O]a–H, where the subscripts a and b represent the number of the hydrophilic and hydrophobic chains respectively. This component was provided by Roig Farma-Fagron (Terrasa, Spain). Isopropyl palmitate (concentration 90%) was provided by Meta (Roig Farma-Fagron). Soy lecithin in powdered form (water content 1.2%, concentration 97%, pH (sol. 1%) 7) was provided by Roig Farma-Fagron. Lecithin is usually used as a synonym for phosphatidylcholine (PC), which is the major component of a phosphatide fraction. It is frequently isolated from soya beans and is com- mercially available in a highly pure state. Isolation and purifi cation of lecithins from dif- ferent sources are described in Kuksis (21) and Prosise (22). PC is a mixture of differently substituted sn-glycerol-3-phosphatidylcholine backbones. The structure of PC is variable and dependent on fatty acid substitution. In the sn-1-position, saturated acyl-groups are more common, and in the sn-2-position, unsaturated species are more common. The sn-1-chain typically shows an average of 16 C, whereas the sn-2-chain shows an average of 18 C. Water used to prepare the formulations was provided by Milli-Q Quality (Milli-Q Academic, Millipore, France). EXPERIMENTAL METHODS Viscosimetry. The viscosity of different formulations was determined by a Brookfi eld DV-II+ digital rotational viscometer immersed in a thermostatic bath maintained at a temperature of 25° ± 0.1°C. This viscometer is a shear rate controlled system therefore the samples are put under a sweep of shear rate (dγ/dt) at regular intervals, allowing variations in viscosity and shear stress to be observed. In order to obtain reproducible results, the samples were always pre-sheared for 60 sec, with measurements being taken after 120 sec. In addition, a viscosimetric study was car- ried out on both the delivery vehicles themselves and the complete formulae containing the active substances. Diffusion experiments. Franz-type cells are commonly used in most published studies (23). The FDC-400 used in our study was supplied by Vidra-Foc (Barcelona, Spain). It consists of two compartments with a membrane clamped between the donor and receiver cham- bers. The receptor phase was a phosphate-buffered saline, at pH 5.6. This pH was chosen because it corresponds to the pH in the areas of the skin where the drug acts after topical administration. The membranes are 47 mm in diameter and 0.45 μm in pore size. Two types of membranes were tested: methylcellulose (Teknocroma) and nylon (Mfd, Waters Corporation).

JOURNAL OF COSMETIC SCIENCE 630 Analytical methods. The concentrations of drugs were measured by UV-spectrophotometry at 223 nm for Aloe vera and at 322 for Hydrocotyle asiatica (λmax). The method was previously validated and verifi ed for accuracy, precision, and linearity. Standard solutions were prepared by diluting the stock solution with phosphate-buffered saline. A UV- spectrophotometer (Perkin-Elmer UV/VIS Lambda 40) was used for all measurements. RESULTS AND DISCUSSION PREPARATION AND ORGANOLEPTIC DESCRIPTION OF FORMULAE In formula one, the base of the hydrogel, provided by BASF, was adapted to our cos- metic active substances (Table I). In the cold production process (4° C ± 0.1), Pluronic F-127® was completely dissolved in the formula, with water added immediately after ad- dition of the active substances. Finally, the process of gelifi cation was carried out at room temperature. Aloe hydrogel at 10% is consistent, transparent, and pink in color, with a characteristic aloe scent. It is easily spread over the skin, leaving a fi ne, transparent fi lm that is quickly absorbed. It does not leave behind a sticky feeling and can be washed off with water, leav- ing the skin soft and smooth. The hydrogel with Hydrocotyle asiatica at 7% differs in color from the Aloe hydrogel. It is slightly orange in appearance and has its own distinctive aroma. Our reference for the study of the organogel was the formula published by Pince (24), which we adapted for the incorporation of the two active principles. A solution of lecithin in isopropyl palmitate and a gel of Pluronic F-127® at 30% were prepared separately and then mixed using gentle electromagnetic agitation (800 rpm). The remaining components were added dur- ing homogenization and then left to cool to obtain the fi nal organogel. No signifi cant organoleptic differences between the Aloe organogel and the Hydrocotyle asiatica organo- gel were observed. Both were creamy, with a viscous consistency, without bubbles, and Table I Composition of Hydrogels Hydrogels Aloe gel side 10:1 10 g Hydrocotyle asiatica 7 g Propylene glycol 19,8 g Propylene glycol 19,8 g Pluronic F-127® 18 g Pluronic F-127® 20,46 g Distilled water 52.2 g Distilled water 52.7 g Table II Compositions of Organogels Organogel PLOs Aloe gel side 10:1 10 g Hydrocotyle asiatica 7 g Propylene glycol 13.5 ml Propylene glycol 14 ml Lecithin/IPP 19.8 ml Lecithin/IPP 20.4 ml Pluronic F-127® 30% gel 56.7 ml Pluronic F-127®30% gel 58.6 ml