Mechanics of Blood Cells with Marginal Band: Competition between Cortical Tension and Rigidity

The fast blood stream of animals is associated with large shear stresses. Consequently, blood cells have evolved a special morphology and a specific internal architecture allowing them to maintain their integrity over several weeks. Non-mammalian red blood cells, mammalian erythroblasts and platelets in particular have a peripheral ring of microtubules, called the marginal band, that flattens the overall cell morphology by pushing on the cell cortex.We modeled how the shape of these cells stems from the competition between marginal band elasticity and cortical tension. We predict that the diameter of the cell scales with the total microtubule mass, and verify the predicted law across a wide range of species. Our analysis also shows that the combination of the marginal band rigidity and cortical tension increases the ability of the cell to withstand forces without buckling. Eventually, we show that the buckling of the marginal band observed during platelet activation is caused by a rapid increase of the cortical tension.