Thermoelasticity of red blood cell membrane

Abstract

The elastic properties of the human red blood cell membrane have been measured as functions of temperature. The area compressibility modulus and the elastic shear modulus, which together characterize the surface elastic behavior of the membrane, have been measured over the temperature range of 2-50 degrees C with micropipette aspiration of flaccid and osmotically swollen red cells. In addition, the fractional increase in membrane surface area from 2-50 degrees C has been measured to give a value for the thermal area expansivity. The value of the elastic shear modulus at 25 degrees C was measured to be 6.6 X 10(-3) dyne/cm. The change in the elastic shear modulus with temperature was -6 X 10(-5) dyne/cm degrees C. Fractional forces were shown to be only on the order of 10-15%. The area compressibility modulus at 25 degrees C was measured to be 450 dyne/cm. The change in the area compressibility modulus with temperature was -6 dyne/cm degrees C. The thermal area expansivity for red cell membrane was measured to be 1.2 X 10(-3)/degrees C. With this data and thermoelastic relations the heat of expansion is determined to be 110-200 ergs/cm2; the heat of extension is 2 X 10(-2) ergs/cm2 for unit extension of the red cell membrane. The heat of expansion is of the order anticipated for a lipid bilayer idealized as twice the behavior of a monolayer at an oil-water interface. The observation that the heat of extension is positive demonstrates that the entropy of the material increases with extension, and that the dominant mechanism of elastic energy storage is energetic. Assuming that the red cell membrane shear rigidity is associated with "spectrin," unit extension of the membrane increases the configurational entropy of spectrin by 500 cal/mol.

Measurement of red blood cell mechanics during morphological changes

“…They are 7.4 AE 0.9 (DC), 10.4 AE 2.9 (EC), and 12.6 AE 2.1 (SC) in μNm −1 . These values are consistent with earlier work based on micropipette aspiration (16), optical tweezers (30), and magnetic twisting cytometry (6). In the latter case we find that, by assuming the ferrimagnetic beads contact the membrane over a ð2.…”

“…1 D-F). The average elastic constant measured for DCs, k e ¼ 1.9 μN∕m, is a factor of 3.5-10 lower than what was measured by micropipette aspiration (16) and electric field deformation (5). However, the quantitative theory discussed below and used to analyze our data generates elastic constants for DCs in good agreement with previous work.…”

Red blood cell thermal fluctuations: comparison between experiment and molecular dynamics simulations

“…We also established that trere was no correlation between the temporal behaviour of the applied pressure and that of the fluctuation modes, which means that the fluctuation modes (and therefore 90 the membrane bending modulus) are not affected by the external pressure. Whilst the values obtained for the membrane bending rigidity are of the same order of magnitude as those reported in previous studies of the long-wavelength regime, the shear modulus obtained, 3.6 × 10 −6 N m −1 , is closer to the values 20 reported in static deformation experiments, such as micropipette aspiration 4 and optical tweezers studies [5][6][7] . This seems to contradict previous conclusions 2 that freely flickering RBCs, i.e.…”

Statistical Mechanics of Thin Spherical Shells

“…The red blood cell membrane is composed of a lipid bilayer with bending rigidity κ 0 ≈ 6-40k B T [17,18] and an attached spectrin network, which contributes to a Young's modulus Y 0 ≈ 25 μN=m [16,18], giving the composite system a resistance to shear. For a characteristic size of R 0 ≈ 7 μm, we find…”