Microbubble acoustic cavitation and soft matter

Ali Rezaei

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

This thesis aims to advance our understanding of ultrasound-driven microbubble dynamics, focusing on interactions with viscoelastic media and confined environments. By combining theoretical modeling and experimental observations, we explore microbubble resonance, scattering, and oscillation across different configurations, including bulk media and microchannels. The findings aim to improve the use of microbubbles in clinical applications, enhancing ultrasound imaging and therapeutic precision.

After introducing bubble dynamics and viscoelastic tissue models, Chapter 2 investigates how microbubble oscillations influence the rheological properties of the surrounding medium. Tissue behavior at high strain rates (106 s-1) - typical of microbubble activity - is not well understood. To address this, we examine polyacrylamide (PAM) hydrogels as tissue mimicking material, using microbubbles as probes. By analyzing ultra-high-speed imaging data and fitting them to coated bubble simulations, we extract the shear modulus and viscosity of soft and stiff hydrogels. Results show viscosity is highly strain-rate dependent, while the elastic modulus remains comparable to low-frequency values.

In Chapter 3, the focus shifts to how the viscoelastic medium’s shear modulus influences the behavior of phospholipid-coated microbubbles. Using a Rayleigh-Plesset-type model, we simulate the scattered pressure from bubbles and study the impact of medium elasticity on resonance frequency, harmonic generation, and subharmonic oscillations.

Chapter 4 builds on this by introducing a microbubble scattering spectroscopy technique to experimentally validate simulation findings. We correlate hydrogel stiffness with microbubble resonance frequency, quantify damping, and demonstrate how the gels affect microbubble stability.

Chapter 5 explores microbubbles in confined environments, such as small blood vessels, using silicone microchannels (15-100 µm). Ultra-high-speed imaging reveals a decrease in resonance frequency and increased damping as confinement increases. Optical data on radial oscillations is compared with theoretical predictions.

Together, these studies enhance our understanding of how microbubbles interact with soft and structured environments, providing a foundation for more accurate clinical models and improved therapeutic outcomes.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Versluis, Michel, Supervisor
  • Fernández Rivas , David, Supervisor
  • Lajoinie, Guillaume P.R., Co-Supervisor
Award date4 Jun 2025
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-6620-9
Electronic ISBNs978-90-365-6621-6
DOIs
Publication statusPublished - 4 Jun 2025

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