Numerical investigation of ultrasound-driven bubble-induced deformation of spherical solid cells.

Ultrasound-driven bubble motion and the associated viscoelastic spherical cell deformation are studied within a coupled level set and volume-of-fluid (CLSVOF)-based compressible three-phase framework, in which solid deformation is handled through a full Eulerian description. The numerical simulations demonstrate various bubble-cell interaction phenomena, including inverted cone- and mushroom-shaped bubbles, droplet-shaped cells, liquid-jet formation, and bidirectional axial bubble splitting, by systematically varying the elastic shear modulus and initial bubble-cell distance. Effective bubble-cell interaction occurs when the initial bubble-cell distance falls below the maximum expansion radius of a free bubble under identical ultrasonic conditions. The potential cell damage mechanisms induced by ultrasound-driven bubble motion are shown to depend strongly on the shear modulus. The cell deformation is further analyzed as a function of cell size and ultrasonic pulse amplitude, revealing that cell size significantly influences cell deformation through its effect on the effective repulsion and attraction surface areas. The present results highlight that large cell deformation associated with potential cell disruption or sonoporation can be effectively regulated, for cells with a given size and shear modulus, by adjusting the initial bubble-cell distance, while for relatively stiff cells (G≥1MPa) such regulation shifts the critical cell size at which liquid-jet-induced deformation may lead to cell damage. It should be noted that the present analysis is limited to the first oscillation cycle (expansion-collapse-jet impact), as post-collapse dynamics do not achieve full grid convergence. Consequently, multi-cycle bubble dynamics and cumulative cell deformation are not considered in this study.