Native bubble nuclei for acoustic cavitation in 3D cell cultures

Abstract

The safety of biomedical ultrasound largely relies on controlling cavitation bubbles in vivo; however, bubble nuclei in biological tissues remain unexplored compared to water. No previous studies have observed where bubble nuclei form in tissues at a microscopic level or how the variation in tissue biomechanical properties can impact the presence of bubble nuclei for acoustic cavitation. In this study, we evaluated whether bubble nuclei form intracellularly or extracellularly in rat epithelial hepatoma (McA-RH7777) and musculoskeletal myoblast (L6) cell lines (n = 5 each), cultured in 3D using Matrigel™ scaffolds. A 3.68 MHz focused ultrasound transducer with f# = 1 was used to induce low-density cavitation using varying pulse lengths (10 to 100 μs) with pressures ranging up to p+ = 29 and p− = 12 MPa. The spatial location of the bubbles was monitored microscopically using high-speed photography at 20 000 fps. Despite significant radiation force on the cell scaffold, preliminary results show that acoustic cavitation bubbles (r = 20 μm approx.) preferentially form extracellularly near the cell membranes. This result suggests that the hydrophobicity in the amphipathic cell membrane may contribute to bubble nuclei formation. Future work includes investigating the distribution of bubble nuclei in healthy versus cancerous cell cultures. [Work supported by NSF CAREER 1943937.]