Effects of phase transition of a lipid bilayer on dynamics of bubble liposomes

Five types of gas-encapsulated liposomes (bubble liposomes) were produced and their stability was studied under static pressure and dynamic pressure conditions. Five types of phosphatidylcholine, DOPC, POPC, DMPC DPPC and DSPC, with different transition temperatures between liquid-crystalline and gel phases in the range from -22°C to +55°C were used as a main component of the liposomes. Static stability of these BLs was evaluated by observations of turbidity of their suspension, and dynamic stability was evaluated by measurements of pressure-dependent ultrasound transmission. The results showed that both stabilities have strong dependence on temperature of bubble suspensions, suggesting that the phase of the shell material is one of the main parameters to determine bubble stabilities. Bubbles with shells in gel phase have higher stability under exposure to ultrasound, suggesting that the intact shell in this phase can be restored immediately after bubble oscillation.