Nebulisers for the generation of liposomal aerosols

Multilamellar liposomes and latex spheres have been atomised using a range of jet and ultrasonic nebulisers. Studies with spheres indicated that relatively large particles can be delivered from nebulisers, although the smaller the suspended particle size, the more efficiently they are delivered from all nebulisers. The size of aerosols generated from liposome suspensions, as measured by laser diffraction, was determined by the lipid concentration and the nebuliser used, but was independent of liposome size and bilayer composition. Generation of aerosols by both jet and ultrasonic nebulisers resulted in damage to liposome structures, with a consequent reduction in the measured vesicle sizes. The Respirgard II jet nebuliser produced aerosols with the smallest median droplet size and caused the greatest damage to liposomes. However, the size of droplets produced by the nebuliser is not the only determinant of liposome stability during atomisation. Relatively fluid EggPC liposomes experienced the greatest disruption during nebulisation. Inclusion of cholesterol or DPPC in the liposome bilayers rendered them more resistant to the disruptive forces to which they were exposed during either jet or ultrasonic nebulisation.