Mechanical characterization of human red blood cells by robotic manipulation with optical tweezers

Human red blood cells (RBCs) are responsible to transport oxygen and carbon dioxide for human bodies. The physiological functions of RBCs are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. In this paper, to understand the correlation between the cell properties and their osmotic environments, robotic manipulation technology with optical tweezers is used to stretch human RBCs in hypotonic conditions. The swollen RBCs are stretched at different levels of laser powers by a single optical trap. The induced deformation responses are recorded for analysis. To extract the mechanical properties from the force-deformation relationship, a mechanical model is developed from our previous work [29]. This model is based on membrane theory and adopts Evans-Skalak material to represent the deformation behavior of RBC membrane. By fitting the modeling results to the experimental data, the area compressibility modulus and elastic shear modulus are characterized as 0.29 ± 0.05 N/m and 6.5±1.0μN/m, respectively, which are less than the reported results of the natural RBCs in the isotonic solution. This preliminary study indicates that the hypotonic environment makes human RBCs become much softer and more deformable, and further, may provide insight into the pathology of some human diseases and disease therapy.