Development and characterization of microemulsions containing hyaluronic acid.

Tween80 and Span20 were used as surfactant mixture for developing non-ionic microemulsions (MEs) containing hyaluronic acid 22 kDa (HA). The effect of Tween80:Span20 ratio (T:S ratio) on microemulsion (ME) water intake and stability was studied. Moreover, the effect of HA on the consumed surfactant amount which is for stabilizing the MEs, for reducing water intake was investigated. Two W/O MEs containing HA were optimized. The first ME was composed of 2% HA, 13.8% Tween:80:Span20 (2:3), 4.2% water and 79.9% isopropylpalmitate (IPP). The second was composed of 2% HA, 16% Span20, 9.6% water:dimethyl sulfoxide (W:DMSO) (6:3.6) and 72.4% medium chain triglycerides (MCTG). The droplet sizes of MEs were determined using dynamic light scattering (DLS). The multilayer membrane system (MLMS) was used for testing the release of HA from both MEs and the released amount of HA was quantified using capillary zone electrophoresis (CZE). Furthermore, three phase diagrams and relevant rheological characteristics were generated. The droplet size of the ME without HA decreased and increased with increasing the temperature. Furthermore, the droplet size of the IPP-ME and MCTG-ME without HA and of the MCTG-ME with HA decreased with increasing temperature. In contrast to this results, the droplet size of the IPP-ME with HA increased with increased temperature. This ME belongs to the Newtonian fluids. Compared to the first ME, the second ME shows droplet sizes at 25 °C of 6.5 nm without and 37 nm with HA. The droplet size in the second ME decreased proportionally with an increase of the temperature with and without HA. The release of HA was faster from the IPP ME compared to the MCTG-ME. The two developed MEs were stable, isotropic and their properties comply with ME properties concerning the droplet size and viscosity.