Exploring the Biological Activities of Ionic Liquids and Their Potential to Develop Novel Vaccine Adjuvants.

Ionic liquids (ILs) are salts with poorly coordinated ions, allowing them to exist in a liquid phase below 100 °C or at room temperature. Therefore, they are best described as room temperature ionic liquids (RTILs). In ionic liquids, the presence of a delocalized charge in at least one ion, coupled with an organic component, inhibits the establishment of a stable solid crystal lattice. Due to their flexible properties and several distinctive characteristics, such as high ionic conductivity, high solvation power, thermal stability, low volatility, and recyclability, ILs have been extensively used in chemical industries. In addition to their various other applications, they also hold potential for drug formulation development. Ionic liquids can be used as solubility enhancers, permeability enhancers, stabilizers, targeted delivery inducers, stealth property providers, or bioavailability enhancers. Moreover, ILs hold significant potential in vaccine formulation. Many new vaccines are in the pipeline with different types of antigens; however, the existence of only a limited number of adjuvants hinder their potential use. Thus, developing new, highly effective, low-cost adjuvant preparations is a central interest among formulation scientists. With their unique properties and biological functions, ILs can be highly promising candidates for new types of vaccines.