Biophysical interactions between therapeutic ultrasound and live cell

Abstract

Therapeutic ultrasound employs the acoustic energy carried by high-frequency mechanical wave to induce beneficial effects on living systems. This therapeutic approach is advantageous in that its energy could be remotely focused on the targeted tissue in a non-invasive manner. Although ultrasound therapy has been shown to be feasible and effective in both laboratory experiments and clinical trials, its safety and efficacy are still challenged by the lack of fundamental knowledge of how ultrasound wave exerts physical effects on the cell system and how the cell functionally responds to the ultrasound stimulation. Motivated by the above insight, this thesis aims to provide direct experimental evidence for illustrating the biophysical details of how ultrasound wave (alone or combined with microbubble) interacts with live cells. An acoustic experimental platform with well-calibrated ultrasound field and live-cell imaging modality was developed to observe ultrasound-cell interaction. Based on this platform, a series of single-cell studies was then conducted to monitor the structural and functional changes of the live cell as well as its fluorescently-labelled components over the course of ultrasound exposure. Results obtained in this thesis provided image-level evidence for characterizing the ultrasound-cell interactions in the following three aspects. First, it was found that low-intensity ultrasound pulsing could directly perturb the plasma membrane, the cytoskeletal network and the inner nucleus of live neuroblastoma cells. This cytomechanical perturbation would result in reversible and structural alternations of subcellular components. Second, low-intensity pulsed ultrasound, when applied on neuronal cells, could exert morphological impact through inducing neurite retraction and cell body displacement, and electrophysiological impact in the form of membrane depolarization and calcium influx. This finding verified the potential of ultrasound in modulating neuronal development and excitability. Last, the cell membrane perforation and resealing dynamics induced by the ultrasound-activated microbubble were visualized and characterized. The subsequent cellular responses to this ultrasound-induced sonoporation were also identified at both membrane and cytoskeleton levels. The significance of this study is to provide direct and solid experimental evidence for understanding the biophysical interactions between ultrasound wave and live cell. This advanced scientific interpretation is definitely crucial for establishing the cellular mechanisms of therapeutic ultrasound and for providing technical insights into ultrasound treatment.