Mechanical properties of bovine aortic endothelial cells in suspension studied by ultrasonic interferometry

Objective: Cell adhesion phenomenon has been extensively studied in the last decade and was shown to be mediated by specialized molecules and driven by physical forces. Cohesion of the vessel wall cells is also dependent on adhesion molecules but less is known about the physical forces involved. To investigate endothelial cell/endothelial cell interaction from a mechanical point of view, we have used an ultrasonic interferometry device, named EchoCell, which has been previously designed to study red blood cell-red blood cell (RBC-RBC) interaction. Methods: Bovine aortic endothelial (BAE) cells were cultured, detached, then suspended in buffer and their mechanical and geometrical properties studied with the EchoCell system. The ultrasonic apparatus measures both the accumulation rate of cells in suspension on a solid plate and the acoustical impedances of the suspension and the sediment. Results: In suspension, BAE exhibited, in our experimental conditions (3×106 cells per ml), a spherical size evaluated by calculation at a mean radius of 7±2 μm. Moreover, no BAE aggregation occurred at the concentrations used. The acoustical impedance of the BAE suspensions calculated from all the samples studied, in the cell concentration range from 1.5×106 to 6×106 cells per ml, was 1.52×106 Rayl (kg m-2 s-1). Furthermore, the acoustical impedance of the cell sediment was found to be independent on the initial cell suspension concentration and equal to 1.63×106 Rayl (kg m-2 s-1). Estimation of the volume fraction of BAE inside the sediment allows to evaluate the ultrasonic velocity and the elastic bulk modulus of cells. Conclusion: The ultrasonic interferometry method appears particularly interesting to study geometrical and mechanical (acoustical impedance, sound velocity, elastic bulk modulus) properties of BAE cells.