Microbubble lipid shell elasticity: Simulation and measurement

We show here that the phospholipid composition of a microbubble shell can significantly affect microbubble dynamics by changing shell viscoelastic properties. We fabricate gold nanoparticle templated microbubbles with varying lipid shells (DPPC, DSPC, DAPC and DBPC). Individual microbubbles undergo nanometer scale radial oscillations that are photothermally activated using a short laser pulse and monitored using forward light scattering. Shell elasticity and viscosity were determined for each microbubble by finding the eigenfrequency and damping ratio when modelling the microbubble as an underdamped, linear oscillator. Elasticity was found to increase with longer lipid acyl chain length from 16 to 20 carbons, and modeled by considering the intermolecular forces. Viscosity, on the other hand, was not found to change significantly for these shells. Interestingly, we observed an increase in elasticity and decrease in viscosity for lipid shells of 22 carbons. These results illustrate key interrelationships between microbubble composition, structure and dynamic behavior that may be used to facilitate their rational design for contrast-enhanced ultrasound and other applications.