M.Sc Thesis

M.Sc StudentElaimy Rasha
SubjectTracking the Dynamics of Membranes Subjected to Ultrasound
by Interferometric Methods
DepartmentDepartment of Biomedical Engineering
Supervisor PROFESSOR EMERITUS Eitan Kimmel
Full Thesis textFull thesis text - English Version


The therapeutic use of ultrasound (US) is investigated intensively in the last two decades. However, explaining the mechanisms of how US affects biological cells and tissues remains unclear. The model of intra-membrane cavitation, which is denoted here as Bilayer Sonophore (BLS), based on US induces pulsating gas pockets in the intra-membrane space between the two lipid leaflets. Resultantly, the acoustic energy is transformed into distortions and strains in the cellular structure. Moreover, the BLS may potentially explain both cavitational and non-cavitational US-induced bio-effects. In order to validate the sonophore model and to study the response of cell membrane subjected to acoustic stimulation, a wide-field digital interferometry (WFDI) technique is used. WFDI is a label-free holographic technique that captures the complex wavefront (phase and amplitude) of the sample field, containing the quantitative phase profile of the sample and gives a three-dimensional cell morphology map. A piezoelectric tube transducer of 1MHz frequency is used and acoustic pressure amplitudes in the range of 150kPa are quantified. The sonication time is ten minutes. Reconstructed images are obtained by an efficient digital process. We use the resulted images to quantify the cell morphological change. Three dimensional representations of the cell thickness are obtained. A quantitative analysis of the cross sectional area of the cell was performed. During the US transmission a morphological change of the examined endothelial cells (ECs) was observed. The measured cell thickness, based on phase profiles, were significantly increased in the nucleus region (9 %± 2%). Consequently the cross-sectional area of cells became significantly smaller compared to their initial area. Two mechanisms of force transmission between US and cells were considered as might be responsible for the morphological change: the tension force, formed in the membrane due to sonophore generation, and the radiation force. We predict that the geometrical change is attributed to the tension force formed in the membrane according to an estimated forces value, which might results in two elementary mechanisms: changing the membrane curvature due to tension, and changing the membrane curvature due to the detachment of FA contacts. However, we presume that most of the change occurs in the lower part interface, the surface between the cell and the plate, owing to the rearrangement (generation and detachment) of the FA points. Accordingly, the change in the cross-sectional area may be explained relying on the detachment of the FA contacts that led to higher values of cell thickness and to a more spherical shape.