Mechanical Properties of the Red Cell Membrane: II. Viscoelastic Breakdown of the Membrane

A technique is described for measuring the stress required to rupture the red cell membrane. It requires a measure of the pressure and time to suck a cell into a micropipette. If a long tongue is pulled into a micropipette, the membrane spontaneously collapses on itself, as does a cylinder of fluid of length equal to its diameter, and a small refractile globule and a swollen red cell are produced. If the cells are hypotonically swollen enough, they cannot afford enough area for a long tongue to move into the pipette and when stressed for a time, hemolyse and disappear into the pipette. Calculation of membrane tension shows that the membrane can withstand a wide variety of tensions, up to a maximum of 20 dynes/cm for short periods of time, but even at much lower stresses the membrane eventually either ruptures, and the cell hemolyses, or relaxes; there does not appear to be a yield stress. This observation and the kinetics of the cell breakdown lead to a viscoelastic model of the cell membrane. The membrane substance has a Young's modulus of approximately 10⁶ to 10⁸ dynes/cm² and a viscosity of 10⁷ to 10¹⁰ poises. This confirms and extends the viscoelastic model proposed by Katchalsky et al. (3).