Ionic Liquid‐Based Microemulsions: A Versatile Platform for Transdermal Delivery

Ionic liquid‐based microemulsions (IL‐MEs) have emerged as versatile nanocarriers for pharmaceutical applications, particularly transdermal drug delivery. Conventional transdermal formulations are limited by the formidable barrier function of the stratum corneum, which restricts drug permeation and hinders the effective delivery of poorly soluble drugs and labile biomolecules. Although conventional microemulsions provide thermodynamic stability and enhanced drug solubilization, their broader application may be restricted by limited single‐phase regions and insufficient solubilization capacity for highly polar compounds and biomacromolecules. By integrating the tunable physicochemical properties of ionic liquids with the thermodynamic stability and organized nanostructures of microemulsions, IL‐MEs provide a highly adaptable platform for transdermal drug delivery. These systems can improve the solubility and physicochemical stability of small‐molecule drugs, proteins, and other bioactive agents while concurrently enhancing their permeation across the skin. Functioning simultaneously as solubilizing media and permeation enhancers, IL‐MEs promote drug dissolution, perturb the organization of stratum corneum lipids, and facilitate transcutaneous transport. This review summarizes recent advances in the formulation, physicochemical characterization, skin‐permeation mechanisms, and therapeutic applications of IL‐MEs, with particular emphasis on the synergistic roles of ionic liquids and microemulsion nanostructures in advancing next‐generation transdermal drug delivery.