Cationic liposomes are spherical structures that contain positively charged lipids. Cationic liposomes can vary in size between 40 nm and 500 nm, and they can either have one lipid bilayer (monolamellar) or multiple lipid bilayers (multilamellar).[1] The positive charge of the phospholipids allows cationic liposomes to form complexes with negatively charged nucleic acids (DNA, mRNA, and siRNA) through ionic interactions.

Ionic interactions arise from electrostatic attraction between two groups of opposite charge. ... These interactions do not produce true “bonds,” since there is no sharing of electrons between the groups involved. The groups are pushed together by their “expulsion” from the polar medium.