Development and application of an osthole microemulsion hydrogel for external drug evaluation

The aim of the study is to provide a new type of drug delivery, combining the advantages of a microemulsion with the transdermal administration of osthole. Appropriate oil phases, surfactants, and cosurfactants were screened by their solubility, transmittance, etc. The appropriate microemulsion ratio formula was selected by measuring the area of the formed microemulsion region from the pseudoternary phase diagram among the different proportions. After measuring the pH, zeta potential, particle size, etc., a 2% osthole drug-containing microemulsion was prepared, and transdermal experiments were performed using a Franz cell. To select a microemulsion formula with high stability and a high skin transmittance rate, 65% distilled water (w/w) was embedded into the microemulsion (7% IPM (w/w), 14% Tween 80 (w/w) and 14% Labrasol (w/w)), and the microemulsion gel was made with different proportions of carbomer. The structure, water content and molecular stability of the microemulsion gels were measured by TEM and DSC. Transdermal experiments were then performed using Franz cells, and these microemulsion gels were applied to determine the subcutaneous residual amounts and optimal skin penetration microemulsion formulations. Thereby, the best microemulsion gel formulation was selected.