Oscillations of polymeric microbubbles: effect of the encapsulating shell

Area of Science:

• Acoustic physics
• Materials science
• Biomedical engineering

Background:

• Ultrasound contrast agents utilize encapsulated gas bubbles.
• Understanding bubble oscillation is crucial for their acoustic behavior.
• The shell material properties significantly influence bubble dynamics.

Purpose of the Study:

• To develop a theoretical model for the oscillation of gas bubbles within a thin shell.
• To apply this model to an experimental ultrasound contrast agent.
• To estimate the viscoelastic properties of the shell material.

Main Methods:

• Developed a theoretical model incorporating shell thickness, shear modulus, and shear viscosity.
• Applied the model to analyze acoustic attenuation measurements of encapsulated air bubbles.
• Compared theoretical calculations with experimental data at linear oscillation amplitudes.

Main Results:

• A good fit was achieved between the theoretical model and experimental acoustic attenuation data.
• Estimated shell shear modulus: 10.6–12.9 MPa.
• Estimated shell viscosity: 0.39–0.49 Pas.
• Shell thickness was approximately 5% of the particle radius.
• Encapsulated bubbles were ~20 times more rigid than free air bubbles.
• Oscillations were heavily damped with Q-values around 1.

Conclusions:

• The encapsulating shell strongly dictates the acoustic behavior of the gas bubbles.
• Bubble stiffness and viscosity are primarily determined by the shell material, not the gas core.
• The developed model accurately predicts the behavior of polymer-shelled microbubbles.