Mechanical properties of bovine erythrocytes derived from ion current measurements using micropipettes.

Synchronized data from ion currents and optical microscopy have been used to measure the mechanical properties of individual soft microparticles. This new experimental method draws on the signals generated by each particle as it passes through the tip of a pipette. The technique represents an advance on micropipette aspiration (MA), which uses optical microscopy in isolation. The ionic resistance through the tip provides additional information regarding the progress of particle deformation. The augmented technique is demonstrated by studying aspiration of individual bovine erythrocytes into a micropipette. Effective mechanical properties have been deduced by using the ionic current response to measure the dwell time and velocity of erythrocytes. Values obtained for the effective viscosity represent liquid-like deformation of the whole cell, and show a consistent shear thinning effect. The effective elasticity also varies with applied force, and was higher for erythrocytes stored for several weeks. The data show that wall friction is an important factor for the uptake dynamics, and that the erythrocytes were damaged or ruptured when passing through pipettes of opening diameter 0.7 μm, the smallest used. These results demonstrate a new approach to measuring the mechanics of individual bioparticles.