Fig. 7. Structure of lipid nanoparticles (LNPs) and lipid components employed in currently available COVID-19 mRNA vaccines.

LNPs are composed of four components: ionizable lipid, helper lipid, cholesterol, and PEGylated lipid. Binding with mRNA occurs by the ionizable lipid that occupies the central core of the LNP. PEGylated lipid is found on the surface of LNPs along with helper lipid forming the bilayer. Cholesterol, charged ionizable lipids, and neutral ionizable lipids are distributed throughout LNPs. The confirmed or the most likely chemical structure of ionizable lipids employed in COVID-19 mRNA vaccines developed by Moderna, BioNTech, CureVac, Arcturus, Imperial College London, and Chulalongkorn University.²⁸⁹ *Molar lipid ratio (%) of ionizable lipid: helper lipid: cholesterol: PEGylated lipid; **NA: Not applicable