Polyacrilic acid derivatives are used as constituents of hydrogels in the preparations for dermatologically and cosmetically application. Gels are made relatively simply and are featured by good stability, clarity, and compatibility with a number of dermatologically and cosmetically active substances. Different types of polyacrilic acid derivatives differ among themselves by their molecular mass, degree of plotting, molecular structure and thereof, the result is gels of diversified properties.

The objective of the paper was formulation and characterization of hydrogels containing various polyacrilic acid derivatives (Carbopol®-BF Goodrich-USA, Tego Carbomers®-Goldschmidt, Germany), as carriers for Aloe Vera gel. To produce the gel were used Carbopol® 934P, Carbopol® 940, Carbopol® Ultrez 10 Polymer and Tego Carbomer® 140 (Gels 1-4) in concentration of 1%. All hydrogels were made with distilled water (pH Jug IV) by adding 5% glycerol (humectans), 1% trietanolamine-polyacrilic acid neutralizing agent and 3% Aloe Vera gel (Terra USA).

The organoleptic properties of the gel were observed for 6 months, pH value (pH- meter H-8417 Hanna Instrument USA) and rheological behavior (rotating viscosimeter Rotovisko RV-12, Haake, Germany). pH Values of the produced gels ran within the limits 5.26-5.92. The gels had satisfactory clarity and indicated plastic flowing type with expressed tixotropy.

Measuring parameters were determined 48 hours, 7 days and 1.3 and 6 months after the samples having been made which were preserved at t=20 (±2)°C, packed in aluminum tubes. During the period of observation no changes occurred in their organoleptic properties, pH value of all gels was within the limits ±0.3 pH units from initial value. Rheological behavior remained the same, as it was 48 hours after the gels being made. The values of relative viscosity with all gels after 6 months of confinement compared to the initial values were insignificantly lower. It can be concluded that all polyacrilic acid derivatives can be used as carriers for Aloe vera extract.

Gel type preparations and especially hydrogels have very wide range of application in dermatotherapeutics and cosmetics. They are produced relatively fast, simple by their composition, low costly products, well adhering to skin, provide well fixing of the carrier, are not irritant at application spot, easily washed off from the skin surface and biopharmaceutical assays indicated better release of many drug substances from the gel compared to ointments and creams. By selecting gelling component, a desired surface and undersurface activity of the preparation can be achieved.

As constituents of hydrogels most frequently are used alginates, gelatins, cellulose derivatives, bentonite, colloidal sillicium dioxide, polyvinil-pyrolidon, polyvinyl alcohol, polyacrilic acid-Carbomer (Ph.Eur.1997). The application of polyacrilic acid derivatives as gel constituent began in the sixties. Polyacrilic acid as negative polyelectrolite of large molecular mass contains a number of hydrophilic groups, dissociates when the base is added whish leads to electrostatic response of negatively electrically empowered groups, voluminous spreading of molecules and gel formation. Various types of polyacrilic acid derivatives differ among themselves by their molecular mass, degree of plotting molecular structure and thereof provide different property (1).

Hydrogels are used as vechiculums for antibiotics, corticosteroides, nonsteroides anti-inflammatory substances, antimycotics, and hormones. In cosmetics the hydrogels march are vitamins, herbal extracts, skin moisturising agents, protein hydrolizates, UV absorbers, antiseptics.

Due to their ability to elevate skin moisture degree, anti-inflammatory activity and to prevent occurrence of skin hyperpigmentation spots, Aloe vera extract is used in cosmetics and dermatological preparations for diversified applications (2).

The objective of the paper was formulation and characterization of hydrogels containing various polyacrilic acid derivatives (Carbopol®-BF Goodrich-USA, Tego Carbomers®-Goldschmidt, Germany), as carriers for Aloe vera extract.

To produce the gel the following were used: Carbopol® 934P, Carbopol® 940, Carbopol® Ultrez 10 Polymer-BF Goodrich-USA and Tego Carbomer® 140-Goldschmidt-Germany, in concentration of 1%. All hydrogels were made with distilled water (Ph Jug IV) by adding 5% glycerol (humectans), 1% trietanolamine-polyacrilic acid neutralizing agent and 3% Aloe vera gel (Terra USA).

Subject to characterize hydrogels for the period of 6 months were observed organoleptic gel properties, pH value and rheological behavior. Measuring parameters were determined at 48 hours, 7 days, 1, 3 and 6 months upon the samples having been made which were preserved at t=20 (±2)°C, packed in aluminium tubes.

Appearance and gel clarity was visually estimated.

pH Value was determined at pH meter H 8417 Hanna Instrument, USA, by direct procedure, with prior pH meter calibration with standard buffers pH=4 and pH=7. Rheological behavior of the tested preparations (dependency between the rate of shear D and shear stress t, as well as relative viscosity, were followed up at t=20 (±2)°C, at rotating viscosimeter Rotovisco RV 12, Haake, Germany, by using coaxial cylinder sensor system (SVst, Svdin), as recommended by the manufacturer to test semi-solid systems. Resistance was determined in which of the tested systems in predimmensioned cylinders provide movement of prescribed size and shape coaxial cylinder by changing speed within the limit 0-660 rpm. Relative viscosity was determined at the coaxial cylinder running speed of 15 rpm (3).

Comparing the changes, which were followed up in pH value, gel rheological and organoleptic properties, estimation was made along with the comparison of their stability.

pH Value of the produced gels was within the limits of 5.26- 5.92 (Table 1). The gels retained satisfactory clarity and indicated plastic flowing type with expressed tixotropy.

No changes in their organoleptic properties occurred in the gels during the observation period, pH values of all gels was within the limits from ±0,3 pH units from the initial value. The rheological behavior remained the same as it was 48 hours after the gel production. Relative viscosity values with all gels measured at a certain speed (15 rpm) were insignificantly lower after 6 months of confinement compared to the initial ones.

The obtained results indicate that the application of certain polyacrilic acid derivatives and with appropriate technological procedure hydrogels are formed which can be used as Aloe Vera extract carriers (4,5). Optimal carrier for Aloe Vera extract is Carbopol® 934P because get gels the best stability and clarity.

1. Dittigen K., Durrani M., Lehmann K. (1997): Acrylic polymers review of pharmaceutical applications. S.T.P. Pharma Sciences, 7(6), 403-437.

2. Agarvala O.P. (1997): Whole Leaf Aloe Vera Gel, Cosm.& Toil. 112, 88.

3. Introduction in viscosimetry, Haake (1987) (Catalogue).

4. Holland D., (1991): Measuring and interpretating the rheological properties of cosmetic products, Rheology 91, 6, 118-112.

5. B.F.Goodrich (1992): The science of rheology, Pharmaceutically applied. Technical note.