Mechanics of biconcave red blood cells deformed by acoustic tweezers

The deformation of biconcave red blood cells (RBCs) in a fluid environment driven by ultrasonic standing waves is studied theoretically and numerically. The cell contains homogeneous cytosol enclosed by a thin biological membrane. The cell membrane is modeled as a hyperelastic thin shell whose enclosed volume is assumed to be preserved to ensure osmotic equilibrium. Regarding acoustic deformation, the acoustic induced force acting on the cell membrane is calculated based on the acoustic radiation stress theory. The equations governing the interaction of the cell deformation and acoustic wave propagation are then numerically implemented in an axisymmetric finite element framework. The simulation results show that when the biconcave red blood cells are trapped at the pressure node of the acoustic standing wave, they gradually transform into an oblate disc shape with the increase of the acoustic input. Parametric studies are performed to systematically investigate the effects of cell mechanical properties and acoustic wavelength on cell deformation. Given that the mechanical properties of RBCs play an important role in disease development and mechanotransduction, this work is helpful to diagnose RBC-related diseases and study mechanotransduction using acoustic deformation technique.