Biomimetic Lung Surfactant Nanodrops for Acoustic Droplet Vaporization

Acoustic droplet vaporization (ADV) involves the liquid-to-gas phase conversion of a superheated emulsion droplet by ultrasound to form an echogenic bubble. This technology may be useful for medical ultrasound, as nanodroplets small enough to leak through endothelial fenestrations may be converted to echogenic microbubbles for extravascular ultrasound imaging of inflamed and angiogenic vasculature. Additionally, droplets may be transformed to acoustically pulsating microbubbles to enhance ultrasound-guided drug delivery. However, surfactant coverage on the droplet often fails to stabilize the expanding interface during ADV, resulting in transitory microbubbles with limited utility. Here we show that interfacial melting and spreading by lung surfactant during surface dilation can be harnessed to increase the echogenicity and stability of post-ADV microbubbles. Lung surfactant, whose composition in the mammalian lung has been honed over millions of years of evolution, has thus proven to be a superior coating material for ADV droplets, and its biomimicry will be an important step toward clinical translation of ADV in ultrasound imaging and therapy.