Cationic liposomes
The structure of cationic liposomes generally consists of three parts: one or more cationic heads, a linker bond, and a hydrophobic tail. The cationic head mostly contains amino groups, such as amino, methyl or hydroxyethyl substituted quaternary ammonium compound (Table 1). The multivalent polar head group or the polar head with multiple positive charges has higher transfection efficiency and allows the endosome to escape, and the tertiary amine group head has higher transfection activity and lower toxicity than the quaternary ammonium group head. Linkage bonds mainly include ester bond, amide bond and carbamate bond, which determine the chemical stability and biodegradability of cationic lipid molecules. Long-chain aliphatic hydrocarbons in cationic liposomes can significantly enhance the interaction with cell membrane and have high transfection efficiency. And the hydrophobic tails of common cationic liposomes are mainly composed of aliphatic hydrocarbon chains and cholesterol [36].