Long-term physical evolution of an elastomeric ultrasound contrast microbubble

Area of Science:

• Materials Science
• Biomedical Engineering
• Acoustics

Background:

• Crosslinked polymer-shelled microbubbles (MBs) are promising ultrasound-active theranostic agents due to their robust shells and surface modification capabilities.
• Despite their long shelf-life, MB shells undergo subtle modifications affecting their acoustic, mechanical, and structural properties over time.

Purpose of the Study:

• To investigate the long-term morphological and acoustic evolution of elastomeric polyvinyl-alcohol (PVA)-shelled MBs.
• To understand the aging mechanism of PVA MBs by integrating microscopy, spectroscopy, and nanomechanics.

Main Methods:

• Long-term morphological and acoustic analysis of PVA-shelled MBs.
• Utilized confocal laser scanning microscopy, acoustic spectroscopy, and AFM nanomechanics.
• Modeled acoustic property changes using linearised oscillation theory, relating them to shell thickness, viscoelasticity, morphology, and nanomechanics.

Main Results:

• Identified a novel aging evolution in PVA MBs with a crossover time of approximately 50 days.
• Initially, MB stiffness and shell thickness changed significantly due to PVA chain release.
• Subsequently, resonance frequency increased alongside shell thickening and softening.

Conclusions:

• PVA-shelled MBs exhibit complex aging dynamics influencing their theranostic potential.
• This study provides a benchmark for understanding viscoelastomeric bubble aging for personalized medicine applications.