Ionic liquid transdermal delivery system: Progress, prospects, and challenges

In the drug delivery system, the transdermal drug delivery system has the advantages of painless administration, avoiding the first-pass metabolism, sustained therapeutic effect, and good patient compliance. It is a promising treatment method. Transdermal drug delivery systems have made important contributions in medical practice, but its potential as an alternative to oral drug delivery and subcutaneous injection has not been fully realized. Ionic liquids (ILs) are widely used in biomedicine, especially in transdermal drug delivery, because of their unique properties, such as good chemical stability and biocompatibility. ILs can enhance transdermal transcellular and decellular transport, bypass the barrier of the stratum corneum, and destroy cell integrity. Hydrophilic ILs act by opening tight junctions in the stratum corneum, mainly by enhancing fluidization in protein and lipid regions to promote paracellular transport. Hydrophobic ILs improve their distribution into the epithelial membrane by providing channels, thereby promoting the transcellular transport of lipid regions. Therefore, this review summarizes the latest methods and progress for transdermal delivery of ILs.