The acoustic response of phospholipid-coated microbubbles is strongly affected by the viscoelastic properties of their stabilizing shell, which depend on surface dilatation through the lipid packing density. However, no fast, reliable, and user-friendly method currently exists to probe the surface dilatation-dependent shell rheology, similar to the Langmuir trough used for macroscopic flat lipid monolayers. In this work, we present a novel quasi-static method to measure the shell parameters of lipid-coated monodisperse microbubbles as a function of surface dilatation. The method relies on the combination of acoustic attenuation spectroscopy and optical attenuation spectroscopy. Acoustic attenuation spectra, measured as a function of ambient pressure, probes the microbubble resonance, while optical attenuation spectra are fitted with a Mie scattering model to provide an accurate measure of both modal bubble radius and polydispersity index (PDI). This integrated approach enables ultrafast sample characterization within a single second. We demonstrate the potential of the method by reporting shell viscosity, shell elasticity, and the corresponding surface tension curve for several cases including different concentrations of palmitic acid in the shell, and varying medium salinity and medium acidity.
Versluis et al. (Wed,) studied this question.