Generation and characterization of aerosols of dispersed surface active phospholipids by ultrasonic and jet nebulization

Abstract

The aerosolization of a multicomponent lipid mixture extracted from bovine lung lavage (surfactant) was investigated in terms of the humidity dependence of the particle size distribution produced by both an ultrasonic and a jet nebulizer. Two methods, sonication on ice and mechanical vortexing, were used to disperse the lipid mixture in 0.15 M NaCl prior to aerosolization in each nebulizer. No significant separation of the lipid from the aqueous phase occurred during nebulization. For both dispersion methods, the particle size dependence on humidity was affected by the presence of dispersed lipids (concentration ∼ 1.5 mg/ml) compared to the case of 0.15 M NaCl aerosols without surfactants. The aerosol from the jet nebulizer consisted of dry particles, and the typical deliquescent behavior for NaCl particles could be demonstrated when relative humidity was increased above 70%. However, when the lipid mixture was nebulized, no such particle growth was observed up to 95% relative humidity. The emerging aerosol from the ultrasonic nebulizer consisted of droplets due to high humidity. In the case of NaCl, these droplets evaporated and became smaller in size with decreasing humidity. For the lipid-saline mixture, the droplets were much more stable and started to evaporate only below 60–70% relative humidity. Although both ultrasonic and jet nebulizers gave particle size distributions in the range for significant alveolar deposition (0.4–1.5 μm AMAD), the ultrasonic nebulizer aerosol sizes at high humidity were optimal in this respect. Calculations of lipid surface and bulk concentration suggest that a significant part of the observed phospholipid dispersion effects on aerosol size behavior may be related to bulk phase interactions.