Hydrodynamic deformation reveals two coupled modes/time scales of red blood cell relaxation

Abstract

We study the mechanical relaxation behavior of human red blood cells by observing the time evolution of shape change of cells flowing through microchannels with abrupt constrictions. We observe two types of relaxation processes. In the first fast process (s 1 $ 200 ms) the initially parachute shaped cells relax into cup-shaped cells (stomatocytes). These cells relax and reorient in a second relaxation process with a response time of s 1/2 $ 10 s into the equilibrium discoid shapes. The values for the relaxation times of single red blood cells in the population scatter significantly within the cell population between 0.11 s < s 1 < 0.52 s and 9 s < s 1/2 < 49 s, respectively. However, when plotting s 1/2 against s 1 , we find a linear relationship between the two timescales and are able to relate both to the elastic properties of the spectrin cytoskeleton underlying the red cell's plasma membrane. Adenosine Triphosphate (ATP) enhances dissociation of spectrin filaments resulting in a reduced shear modulus. We modify the cytoskeleton connectivity by depletion and repletion of ATP and study the effect on relaxation. Both the linear relationship of timescales as well as the ATP dependence can be understood by theoretical models.

Mechanical differences of sickle cell trait (SCT) and normal red blood cells

“…Fig. 40,43,44 The SCT sample reveals both higher shear modulus and viscosity compared to healthy RBCs. 3(a) and (b).…”

Viscoelastic Transient of Confined Red Blood Cells

“…Early studies have investigated the relaxation of RBC deformation following the removal of an applied mechanical stress: the pioneer work by Hochmuth et al focused on shape recovery in micropipette experiments [26]; Baskurt and Meiselman later performed rheo-optical strain relaxation experiments upon cessation of shear of concentrated RBC suspension [27], and Bronkhorst et al pioneered the use of optical tweezers to conduct shape recovery experiments on single cells [28]. More recently, Guido and Tomaiuolo have performed measurements of RBC response time upon flow start in microchannels [15], and Braunmüller et al have investigated RBC shape relaxation using microfluidic tools [29].…”

Dynamics of fatty acid vesicles in response to pH stimuli

“…1,2 When an elongational flow is dominant, vesicles exhibit tank-treading motion, whereas tumbling of vesicles is observed, when a rotational flow governs the shear flow. They exhibit unique dynamics in response to external stimuli, such as shear flow, electric field, and optical illumination.…”

“…Time dependence of the pH profile around the tip of the micropipette (located at a distance of 0 mm) after the continuous micro-injection of a 50 mM NaOH solution calculated by eqn(1).…”