Ionic Liquids: Momentous Tools in Transdermal Delivery of Biomacromolecules

Abstract Transdermal drug delivery is a promising strategy characterized by minor fluctuations in blood concentrations, few adverse effects, convenience, and excellent patient compliance, especially for biomacromolecules. Conversely, traditional delivery methods are limited by their poor penetration abilities and complex preparation and application techniques. However, some inherent properties of biomacromolecules, such as large sizes, complex structure, and poor stability, can affect their ability to overcome skin barriers and reach deeper layers. Ionic liquids (ILs) are organic salts composed of asymmetric cations and anions in liquid form below 100 °C. ILs provide excellent protection for biomacromolecules and can facilitate their passage through the stratum corneum to cells for therapeutic effects. Therefore, they represent one of the most promising approaches to promoting transdermal penetration. Here, the barriers to effective transdermal delivery, including skin properties and the stability and biocompatibility of IL‐based biomacromolecule formulations, are highlighted and the current status of IL‐based biomacromolecule formulations are focused on, the tremendous advantages of using ILs based on current challenges in transdermal drug delivery are discussed, and light is shed on several ILs frequently used in the delivery of biomacromolecules.