Patent ID: 8871252

Claim:
A pH-responsive liposome comprising as a constituent lipid thereof, at least one of the cationic amphiphilic molecules represented by the following formulae: wherein each n is independently an integer of 8 to 22, and m and k are each independently an integer of 1 to 14, and comprising as a constituent lipid thereof at least one of an anionic amphiphilic molecule and a twitterionic amphiphilic molecule represented by the following formulae: wherein each n is independently an integer of 8 to 22, wherein the liposome, when dispersed in an aqueous medium, has a positive zeta potential in an acidic environment where the dispersion has a pH of less than 6.5, and has a negative zeta potential in a basic environment where the dispersion has a pH of 8.5 or more.