December 29, 2025 by Nagoya Institute of Technology
Collected at: https://phys.org/news/2025-12-showcases-microbubble-behavior-viscoelastic-fluid.html
Encapsulated microbubbles (EMBs), tiny gas-filled bubbles coated in lipid or protein shells, play a central role in biomedical ultrasound. When exposed to ultrasound waves, EMBs contract, resulting in oscillations that enhance image contrast or deliver drugs directly by creating pores in cell membranes via sonoporation. However, while promising for biomedical applications, their behavior is far more complex.
Most existing theories on EMBs assume spherically symmetrical oscillations and only study them in simple Newtonian fluids. However, most biological fluids, such as blood, are viscoelastic (non-Newtonian) fluids. When inside the body, these fluid forces, pressure from vessel walls, and changing ultrasound pulses can influence the behavior of EMBs, affecting both imaging accuracy and treatment safety.
To better understand these effects, a multi-institutional research team has developed a comprehensive computational model that simulates the behavior of EMBs under real biological conditions. The team included Assistant Professor Haruki Furukawa and Professor Shuichi Iwata from Nagoya Institute of Technology (NITech), Japan, in collaboration with Emeritus Professor Tim N. Phillips, Dr. Michael J. Walters, and Reader Steven J. Lind from Cardiff University, Wales.
The work is published in the Journal of Non-Newtonian Fluid Mechanics.
“Most microbubble models assume perfect spheres and Newtonian liquids,” explains Dr. Furukawa. “However, real biological fluids are viscoelastic, so we aimed to develop a model that simulates actual physiological conditions for a more realistic assessment of safety and efficacy.”
Accordingly, the researchers incorporated a non-singular boundary element method that focuses on calculations of the object’s boundaries, combined with the Oldroyd B model that describes rheological behavior in viscoelastic fluids. Using this approach, they simulated a fully non-spherical, time-dependent behavior of a coated microbubble when exposed to pulsed ultrasound near a rigid wall. The coupled approach allowed them to capture key features such as asymmetric deformation, translational motion, and liquid-jet formation, which are usually missed in simple spherical models.
They found that the EMB shell thickness strongly affects bubble stability. Thick shells experienced limited deformation, lowered jet velocity, and produced smaller pressure peaks at the vessel wall. In contrast, thin shells underwent stronger motion and jetting, potentially increasing the risk of tissue damage. The results also revealed how fluid viscoelasticity competes with inertia and shell elasticity and clarified how ultrasound frequency and pressure interact with microbubble design.
“Our framework offers a cost-effective tool to assess microbubble safety,” highlights Dr. Furukawa. “By understanding how shell properties, fluid viscoelasticity, and ultrasound settings influence EMBs, we can better guide design standards for safer diagnostics and more effective targeted treatments.”
More information: H. Furukawa et al, The influence of viscoelasticity on the dynamics of encapsulated microbubbles near a rigid surface forced by ultrasound, Journal of Non-Newtonian Fluid Mechanics (2026). DOI: 10.1016/j.jnnfm.2025.105518
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