Biophys J, July 2000, p. 153-162, Vol. 79, No. 1

Stability Analysis of Micropipette Aspiration of Neutrophils

Jure Derganc,^* Bojan Boi,^* Saa Svetina,^* and Botjan ek^*

 ^*Institute of Biophysics, Medical Faculty, University of Ljubljana, Lipieva 2, SI-1000 Ljubljana and  J. Stefan Institute, Jamova 39, SI-1111 Ljubljana, Slovenia

During micropipette aspiration, neutrophil leukocytes exhibit a liquid-drop behavior, i.e., if a neutrophil is aspirated by a pressure larger than a certain threshold pressure, it flows continuously into the pipette. The point of the largest aspiration pressure at which the neutrophil can still be held in a stable equilibrium is called the critical point of aspiration. Here, we present a theoretical analysis of the equilibrium behavior and stability of a neutrophil during micropipette aspiration with the aim to rigorously characterize the critical point. We take the energy minimization approach, in which the critical point is well defined as the point of the stability breakdown. We use the basic liquid-drop model of neutrophil rheology extended by considering also the neutrophil elastic area expansivity. Our analysis predicts that the behavior at large pipette radii or small elastic area expansivity is close to the one predicted by the basic liquid-drop model, where the critical point is attained slightly before the projection length reaches the pipette radius. The effect of elastic area expansivity is qualitatively different at smaller pipette radii, where our analysis predicts that the critical point is attained at the projection lengths that may significantly exceed the pipette radius.

Biophys J, July 2000, p. 153-162, Vol. 79, No. 1
© 2000 by the Biophysical Society   0006-3495/00/07/153/10  $2.00