Evaluation of the delivery of suspensions from an ultrasonic nebuliser with and without the lung surfactant ‘Exosurf’

Abstract

A multistage liquid impinger (MLI) was used to determine the fraction of spherical particles delivered within the range of 5-0.3 μm, from 0.25% w/w suspensions of five different sizes of spheres alone or together with the lung surfactant ‘Exosurf’ by means of an ultrasonic nebuliser, the fraction of Exosurf delivered was also determined. Only a small proportion of the spheres was delivered to the MLI from suspensions of the spheres. The largest amount collected was 18% w/w of the loaded amount and this was obtained from a suspension of spheres with a nominal size of 0.35 μm. This was in part found to be due to the presence of aggregates of the spheres in the nebulising chamber, which formed during sonication of the suspension. The addition of Exosurf to the suspensions increased the total amount of spheres impacted in the MLI for all the sphere sizes tested. High concentrations of Exosurf increased the proportion of spheres delivered to the MLI most, and large spheres benefitted most from the addition of Exosurf. These results suggested that the formation of aggregates by the nebuliser was reduced when Exosurf was added to the suspension. The amount of Exosurf and spheres delivered to the MLI was also found to have increased when mixtures of spheres and Exosurf were nebulised, possibly due to interactions between the two.