RBC membrane instability for large pipette deformation. A theoretical approach

Under conditions of high pressure difference micropipette aspiration experiments show a "pinch-off" phenomenon as observed by RAND /31/. In a very recent paper, MEIER et. al /9/ have reported about new data obtained with a modern electronic technique under moderate mechanical load. We have theoretically analysed the conditions necessary to form such a instability. In our approximations we have investigated the effective transmembrane pressure difference which is given both by the true pressure drop, determined by the hydrodynamic flow through a small gap between the cell tongue and the pipette wall and the interaction between the tongue and the wall, as well as by the nonisotropic part of the membrane tension. When the membrane tongue is long enough (greater than 3Rp) we have found a condition for the loss of membrane stability in a point where a minimum of the effective transmembrane pressure drop occurs. An expression for it and the vesicle size are given.