Microbubble dispersions of natural lung surfactant

Microbubbles played an important role in R. E. Pattleʹs discovery of lung surfactant and E. M. Scarpelliʹs finding of the foam structure that forms the alveolar surface network. Today, colloidal dispersions of microbubbles coated with the same lipids found in natural lung surfactant are being used for a variety of biomedical applications, including ultrasound imaging, targeted drug delivery and injectable oxygenation. The purpose of this review is to introduce the reader to these two lines of research, in hope that an understanding of the biophysics of natural lung surfactant may inform the materials science of synthetic biomedical microbubbles, and vice versa. Clearly, one can gain a better understanding of synthetic lipid-coated microbubbles by studying Pattleʹs classical descriptions of lung bubbles, as many of the same properties have been observed in these two systems. For example, lung surfactant films on both natural lung bubbles and synthetic microbubbles fracture as they expand and reseal as they compress back to their original area. Additionally, the wrinkle-to-fold collapse transition can be observed on both systems, as it has been on the Langmuir trough and other surface film techniques. Use of the experimental microbubble platform may allow future measurements of lung surfactant permeability to gases and other solutes, as well as surface dilatational mechanics. Conversely, the study of natural lung surfactant monolayers may provide insights into new colloidal dispersions of synthetic microbubbles for medical imaging or drug delivery.