Biomechanics of cell rolling: shear flow, cell-surface adhesion, and cell deformability.

The mechanics of leukocyte [white blood cell (WBC)] deformation and adhesion to endothelial cells (EC) in shear flow has been investigated. Experimental data on transient WBC–EC adhesion were obtained from in vivo measurements. Microscopic images of WBC–EC contact during incipient WBC rolling revealed that for a given wall shear stress, the contact area increases with time as new bonds are formed at the leading edge, and then decreases with time as the trailing edge of the WBC membrane peels away from the EC. A two-dimensional model (2D) was developed consisting of an elastic ring adhered to a surface under fluid stresses. This ring represents an actin-rich WBC cortical layer and contains an incompressible fluid as the cell interior. All molecular bonds are modeled as elastic springs distributed in the WBC–EC contact region. Variations of the proportionality between wall shear stress (τ
 w
 ) in the vicinity of the WBC and the resulting drag force (F

 s
 ), i.e., Fs/τw, reveal its decrease with WBC deformation and increasing vessel channel height (2D). The computations also find that the peeling zone between adherent WBC and EC may account for less than 5% of the total contact interface. Computational studies describe the WBC–EC adhesion and the extent of WBC deformation during the adhesive process. © 1999 Biomedical Engineering Society.
 PAC99: 8717-d, 8719Tt, 8717Aa

Mechanics of leukocyte deformation and adhesion to endothelium in shear flow

http://ley-lab.liai.org/publications/207.pdf

Deformable gas-filled microbubbles targeted to P-selectin.

Computational fluid dynamics is used to investigate the effects of cell deformability and viscoelasticity on receptor-mediated leukocyte adhesion to endothelium or a ligand coated surface in a parallel-plate flow chamber. In the three-dimensional numerical code, a leukocyte is modeled as a compound viscoelastic drop (a nucleus covered by a thick layer of cytoplasm). The nucleus, cytoplasm, and extracellular fluid are considered as Newtonian or viscoelastic liquids of high viscosity. The receptor-ligand interaction is incorporated into the code by using the spring-peeling kinetic model under the assumption that leukocyte receptors are located on the tips of cylindrical microvilli distributed over the leukocyte membrane. The code is based on the volume-of-fluid method, and the Giesekus constitutive equation is implemented in the code to capture viscoelasticity of the cytoplasm and nucleus. Numerical simulations demonstrate the formation and breakup of membrane tethers observed in vitro and suggest that the elasticity of the cytoplasm is responsible for a teardrop shape of rolling leukocytes in vivo. When viewed from the top, as normally occurs during shear flow experiments in vitro, little or no deformation occurs, a side view shows significant deformation in the contact region. We show that the leukocyte membrane can be extended and disrupted under high shear if the receptor-ligand bonds live in a stressed state for a sufficiently long time. If the shear rate is low, the leukocyte rolls along the surface. The rolling velocity of the viscoelastic cell is smaller than that of the Newtonian cell. This is due to the increased deformability of the viscoelastic cell and, as a result, the decreased torque acting on this cell.

Three-dimensional numerical simulation of receptor-mediated leukocyte adhesion to surfaces: Effects of cell deformability and viscoelasticity

We investigate the critical conditions for the onset of motion of a three-dimensional droplet on a wall in shear flows at moderate Reynolds number A diffuse-interface method is used for this purpose, which also circumvents the stress singularity at the moving contact line, and the method allows for a density and viscosity contrast between the fluids Contact-angle hysteresis is represented by the prescription of a receding contact angle θ R and an advancing contact angle value θ A  Critical conditions are determined by tracking the motion and deformation of a droplet (initially a spherical cap with a uniform contact angle θ 0 ) At sufficiently low values of a Weber number, We (based on the applied shear rate and the drop volume), the drop deforms and translates for some time, but subsequently reaches a stationary position and attains a steady-state shape At sufficiently large values of We no such steady state is found We present results for the critical value of We as a function of Reynolds number Re for cases with the initial value of the contact angle θ 0 = OR as well as for θ 0 = θ A  A scaling argument based on a force balance on the drop is shown to represent the results very accurately Results are also presented for the static shape, transient motion and flow structure at criticality It is shown that at low Re our results agree (with some qualifications) with those of Dimitrakopoulos & Higdon (1998, J Fluid Mech vol 377, p 189) Overall, the results indicate that the critical value of We is affected significantly by inertial effects at moderate Reynolds numbers, whereas the steady shape of droplets still shows some resemblance to that obtained previously for creeping flow conditions The paper concludes with an investigation into the complex structure of a steady wake behind the droplet and the occurrence of a stagnation point at the upstream side of the droplet

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112008000190

Onset of motion of a three-dimensional droplet on a wall in shear flow at moderate Reynolds numbers

Multisystem inflammatory syndrome in children (MIS-C) is a life-threatening sequela of SARS-CoV-2 infection. Limited data are available regarding risk-stratification or long-term outcomes in MIS-C. This study sought to determine associations between serologic markers and severity of illness and understand long-term cardiac outcomes. This series includes 46 cases (mean age 8.1 years; 63.0% male) of MIS-C. Pearson's chi-squared analysis showed an erythrocyte sedimentation rate (ESR) greater than 30 mm/h and 50 mm/h were disproportionately associated with pediatric intensive care unit (PICU) admission (χ2 = 4.44, P = .04) and use of vasopressors (χ2 = 6.06, P = .01), respectively. Ferritin less than 175.6 ng/mL was associated with use of vasopressors (χ2 = 5.28, P = .02). There was a negative correlation between ESR and ejection fraction (EF) (r = -0.39, P = .009). Most patients with abnormal echocardiograms had resolution of abnormalities within 30 days. Therefore, inflammatory markers may be helpful in predicting which patients may require specific interventions or experience cardiac dysfunction, but MIS-C does not appear to be associated with complications at 1 year.

https://journals.sagepub.com/doi/pdf/10.1177/00099228231180411

Multisystem Inflammatory Syndrome in Children: Two Years' Worth of Learning.

In vitro side-view imaging technique and analysis of human T-leukemic cell adhesion to ICAM-1 in shear flow

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Multisystem Inflammatory Syndrome in Children: Two Years' Worth of Learning.

In vitro side-view imaging technique and analysis of human T-leukemic cell adhesion to ICAM-1 in shear flow