Interaction of ultrasonically driven bubble with a soft tissue-like boundary

Area of Science:

• Acoustics
• Fluid Dynamics
• Biophysics

Background:

• Bubble dynamics are crucial in various ultrasound applications.
• Understanding bubble-wall interactions is key for optimizing ultrasound therapies.
• Bubble behavior is known to be influenced by external factors like ultrasound parameters and surrounding medium properties.

Purpose of the Study:

• To investigate the size-dependent dynamics of bubbles interacting with soft boundaries under ultrasound.
• To analyze the effects of bubble size, ultrasound frequency, and boundary properties on bubble behavior and boundary response.
• To provide insights for optimizing ultrasound conditions based on bubble and boundary characteristics.

Main Methods:

• Simulations and analysis of three bubble sizes (1.5 µm, 15 µm, 150 µm) near a 1 kPa soft boundary.
• Examination of bubble radial oscillation, center displacement, and shape changes across ultrasound frequencies (5 kHz - 4 MHz).
• Assessment of boundary deflection and stress responses to bubble oscillations.

Main Results:

• Smaller bubbles exhibited reduced inertial motion and maintained spherical shapes.
• Larger bubbles showed significant shape changes, approaching jet formation, with collapse tendencies near their natural frequency.
• Bubble displacement was dependent on soft boundary modulus, while radial amplitude and velocity were minimally affected.
• Softer boundaries experienced less stress, with resonance peaks observed for larger bubbles at specific frequencies.

Conclusions:

• Bubble size and soft boundary properties critically influence ultrasound-induced dynamics.
• Findings offer guidance for tailoring ultrasound parameters for specific applications involving bubble-boundary interactions.
• Optimizing ultrasound conditions requires considering both bubble characteristics and the mechanical properties of the surrounding soft tissues.