Visualizing the Histotripsy Process: Bubble Cloud-Cancer Cell Interactions in a Tissue-Mimicking Environment.

Area of Science:

• Biophysics
• Biomedical Engineering
• Acoustic Medicine

Background:

• Histotripsy is a non-invasive ultrasonic ablation technique utilizing cavitation to mechanically disintegrate tissue.
• The precise cellular mechanisms driving histotripsy-induced tissue fractionation remain incompletely understood.
• Previous hypotheses suggest bubble dynamics during histotripsy induce significant stress and strain on adjacent cellular structures.

Purpose of the Study:

• To visualize and characterize the cellular-level response to histotripsy pulses.
• To test the hypothesis that cavitation bubble dynamics are responsible for tissue fractionation.
• To elucidate the mechanical forces exerted by histotripsy on cells within a 3D matrix.

Main Methods:

• Utilized a custom-built 2-MHz transducer integrated with a microscope stage for high-speed optical imaging.
• Cultured breast cancer cells within a fibrin-based gel phantom to simulate a 3D extracellular matrix.
• Performed numerical simulations using a single-bubble model to complement experimental observations.

Main Results:

• Histotripsy cavitation bubbles formed in the extracellular space, not intracellularly.
• Adjacent cells experienced significant displacement and deformation (>150% strain) during bubble expansion and collapse.
• Cells were repeatedly deformed and bisected by bubble dynamics, particularly during bubble collapse, aligning with simulation predictions.

Conclusions:

• The study provides the first cellular-level visualization of histotripsy-induced tissue fractionation.
• Experimental and simulation results confirm that cavitation bubble dynamics are the primary drivers of cell damage and tissue ablation.
• Findings support the hypothesis that localized stress and strain from bubble collapse explain the sharp lesion margins observed in histotripsy therapy.