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The mechanical properties of erythrocytes have been investigated by different techniques. However, there are few reports on how the viscoelasticity of these cells varies during malaria disease. Here, we quantitatively map the viscoelastic properties of Plasmodium falciparum-parasitized human erythrocytes. We apply new methodologies based on optical tweezers to measure the viscoelastic properties and defocusing microscopy to measure the erythrocyte height profile, the overall cell volume, and its form factor, a crucial parameter to convert the complex elastic constant into complex shear modulus. The storage and loss shear moduli are obtained for each stage of parasite maturation inside red blood cells, while the former increase, the latter decrease. Employing a soft glassy rheology model, we obtain the power-law exponent for the storage and loss shear moduli, characterizing the soft glassy features of red blood cells in each parasite maturation stage. Ring forms present a liquid-like behavior, with a slightly lower power-law exponent than healthy erythrocytes, whereas trophozoite and schizont stages exhibit increasingly solid-like behaviors. Finally, the surface elastic shear moduli, low-frequency surface viscosities, and shape recovery relaxation times all increase not only in a stage-dependent manner but also when compared to healthy red blood cells. Overall, the results call attention to the soft glassy characteristics of Plasmodium falciparum-parasitized erythrocyte membrane and may provide a basis for future studies to better understand malaria disease from a mechanobiological perspective., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Mechanical properties of cells are known to be influenced by the actin cytoskeleton. In this article, the action of drugs that interact with the actin cortex is investigated by tether extraction and rheology experiments using optical tweezers. The influences of Blebbistatin, Cytochalasin D and Jasplakinolide on the cell mechanical properties are evaluated. The results, in contradiction to current views for Jasplakinolide, show that all three drugs and treatments destabilize the actin cytoskeleton, decreasing the cell membrane tension. The cell membrane bending modulus increased when the actin cytoskeleton was disorganized by Cytochalasin D. This effect was not observed for Blebbistatin and Jasplakinolide. All drugs decreased by two-fold the cell viscoelastic moduli, but only Cytochalasin D was able to alter the actin network into a more fluid-like structure. The results can be interpreted as the interplay between the actin network and the distribution of myosins as actin cross-linkers in the cytoskeleton. This information may contribute to a better understanding of how the membrane and cytoskeleton are involved in cell mechanical properties, underlining the role that each one plays in these properties., (Copyright © 2017. Published by Elsevier Inc.)