INFLUENCE OF BIOLOGICALLY ACTIVE ADDITIVES ON THE VISCOSITY OF LAMELLAR LIQUID CRYSTALS

Lamellar mesophases based on lecithin are of interest for the development of topical formulations due to their ability to accommodate components of different polarity and their structural similarity to stratum corneum lipids. Rheological behavior is a key parameter that affects both the application properties and the release profile of active ingredients.

In this work, we investigated how the addition of gelatin and several plant extracts (dioscorea, onion, red wine) modifies the viscous properties of lamellar liquid crystals formed in a quaternary system: lecithin – olive oil – tea tree oil – water. All samples were prepared using a previously developed procedure; the presence of a lamellar mesophase was confirmed by polarized light microscopy. Rheological tests were carried out on a Haake Viscotester IQ rotational viscometer at 25 °C. All compositions exhibited pseudoplastic behavior, i.e., the effective viscosity decreased with increasing shear rate.

Incorporating gelatin solutions at concentrations of 1, 2, 3, and 5 % into the liquid‑crystalline matrix increased the viscosity in the shear rate range 0.01–1.0 s⁻¹ by factors of 1.23, 1.49, 1.58, and 1.79, respectively, compared to the control sample. The most pronounced effect was observed at 5 % gelatin, which can be attributed to the formation of a three‑dimensional gel network within the aqueous interlayers.

Plant extracts also significantly altered the rheological response. The dry extract of dioscorea raised the viscosity by a factor of 1.23 on average, whereas the alcoholic extract of dioscorea gave a 7.5‑ to 13.1‑fold decrease depending on the shear rate. Onion alcoholic extract resulted in a 3.4‑ to 9.6‑fold viscosity reduction. For red wine dry extract, a clear concentration dependence was found: at 1, 2, and 5 % the viscosity increased by factors of 1.40, 1.66, and 2.02, respectively. After two weeks of storage, all samples retained their liquid‑crystalline structure, indicating good physical stability.

The results demonstrate that the rheological properties of lecithin‑based lamellar phases are highly sensitive to the nature and concentration of incorporated additives. These findings provide a basis for tailoring the viscosity and release characteristics of lecithin liquid‑crystalline formulations intended for dermatological and cosmetic use.