Mechanical fluidity of fully suspended biological cells

Mechanical characteristics of single biological cells are used to identify and possibly leverage interesting differences among cells or cell populations. Fluidity---hysteresivity normalized to the extremes of an elastic solid or a viscous liquid---can be extracted from, and compared among, multiple rheological measurements of cells: creep compliance vs. time, complex modulus vs. frequency, and phase lag vs. frequency. With multiple strategies available for acquisition of this nondimensional property, fluidity may serve as a useful and robust parameter for distinguishing cell populations, and for understanding the physical origins of deformability in soft matter. Here, for three disparate eukaryotic cell types deformed in the suspended state via optical stretching, we examine the dependence of fluidity on chemical and environmental influences around a time scale of 1 s. We find that fluidity estimates are consistent in the time and the frequency domains under a structural damping (power-law or fractional derivative)model, but not under an equivalent-complexity lumpedcomponent (spring-dashpot) model; the latter predicts spurious time constants. Although fluidity is suppressed by chemical crosslinking, we find that adenosine triphosphate (ATP) depletion in the cell does not measurably alter the parameter, and thus conclude that active ATP-driven events are not a crucial enabler of fluidity during linear viscoelastic deformation of a suspended cell. Finally, by using the capacity of optical stretching to produce near-instantaneous increases in cell temperature, we establish that fluidity increases with temperature---now measured in a fully suspended, sortable cell without the complicating factor of cell-substratum adhesion

Deformation of a red blood cell in a narrow rectangular microchannel

The deformability of a red blood cell (RBC) is one of the most important biological parameters affecting blood flow, both in large arteries and in the microcirculation, and hence it can be used to quantify the cell state. Despite numerous studies on the mechanical properties of RBCs, including cell rigidity, much is still unknown about the relationship between deformability and the configuration of flowing cells, especially in a confined rectangular channel. Recent computer simulation techniques have successfully been used to investigate the detailed behavior of RBCs in a channel, but the dynamics of a translating RBC in a narrow rectangular microchannel have not yet been fully understood. In this study, we numerically investigated the behavior of RBCs flowing at different velocities in a narrow rectangular microchannel that mimicked a microfluidic device. The problem is characterized by the capillary number Ca, which is the ratio between the fluid viscous force and the membrane elastic force. We found that confined RBCs in a narrow rectangular microchannel maintained a nearly unchanged biconcave shape at low Ca, then assumed an asymmetrical slipper shape at moderate Ca, and finally attained a symmetrical parachute shape at high Ca. Once a RBC deformed into one of these shapes, it was maintained as the final stable configurations. Since the slipper shape was only found at moderate Ca, measuring configurations of flowing cells will be helpful to quantify the cell state.Takeishi, Naoki, Hiroaki Ito, Makoto Kaneko, and Shigeo Wada. 2019. "Deformation of a Red Blood Cell in a Narrow Rectangular Microchannel" Micromachines 10, no. 3: 199. https://doi.org/10.3390/mi1003019

Computational Biorheology of Human Blood Flow in Health and Disease

Hematologic disorders arising from infectious diseases, hereditary factors and environmental influences can lead to, and can be influenced by, significant changes in the shape, mechanical and physical properties of red blood cells (RBCs), and the biorheology of blood flow. Hence, modeling of hematologic disorders should take into account the multiphase nature of blood flow, especially in arterioles and capillaries. We present here an overview of a general computational framework based on dissipative particle dynamics (DPD) which has broad applicability in cell biophysics with implications for diagnostics, therapeutics and drug efficacy assessments for a wide variety of human diseases. This computational approach, validated by independent experimental results, is capable of modeling the biorheology of whole blood and its individual components during blood flow so as to investigate cell mechanistic processes in health and disease. DPD is a Lagrangian method that can be derived from systematic coarse-graining of molecular dynamics but can scale efficiently up to arterioles and can also be used to model RBCs down to the spectrin level. We start from experimental measurements of a single RBC to extract the relevant biophysical parameters, using single-cell measurements involving such methods as optical tweezers, atomic force microscopy and micropipette aspiration, and cell-population experiments involving microfluidic devices. We then use these validated RBC models to predict the biorheological behavior of whole blood in healthy or pathological states, and compare the simulations with experimental results involving apparent viscosity and other relevant parameters. While the approach discussed here is sufficiently general to address a broad spectrum of hematologic disorders including certain types of cancer, this paper specifically deals with results obtained using this computational framework for blood flow in malaria and sickle cell anemia.National Institutes of Health (U.S.)Singapore-MIT Alliance for Research and Technology (SMART)United States. Dept. of Energy. Collaboratory on Mathematics for Mesoscopic Modeling of MaterialsUnited States. Dept. of Energy (INCITE Award

Microconstriction Arrays for High-Throughput Quantitative Measurements of Cell Mechanical Properties

AbstractWe describe a method for quantifying the mechanical properties of cells in suspension with a microfluidic device consisting of a parallel array of micron-sized constrictions. Using a high-speed charge-coupled device camera, we measure the flow speed, cell deformation, and entry time into the constrictions of several hundred cells per minute during their passage through the device. From the flow speed and the occupation state of the microconstriction array with cells, the driving pressure across each constriction is continuously computed. Cell entry times into microconstrictions decrease with increased driving pressure and decreased cell size according to a power law. From this power-law relationship, the cell elasticity and fluidity can be estimated. When cells are treated with drugs that depolymerize or stabilize the cytoskeleton or the nucleus, elasticity and fluidity data from all treatments collapse onto a master curve. Power-law rheology and collapse onto a master curve are predicted by the theory of soft glassy materials and have been previously shown to describe the mechanical behavior of cells adhering to a substrate. Our finding that this theory also applies to cells in suspension provides the foundation for a quantitative high-throughput measurement of cell mechanical properties with microfluidic devices

Atomic force microscopy probing in the measurement of cell mechanics

Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology. Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles. AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options

Pathophysiology of human red blood cell probed by quantitative phase microscopy by YongKeun Park.

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 53-58).There is a strong correlation between the membrane fluctuations and the material properties of living cells. The former, consisting of submicron displacements, can be altered by changing the cells' pathophysiological conditions. It is our hypothesis that the material properties of cells can be retrieved when we quantify cell membrane fluctuation and combine that result with an appropriate physical model. We have developed: (1) an optical imaging technique to noninvasively quantify membrane fluctuations in red blood cells at the nanometer and millisecond scales; and (2) a model to retrieve the material properties of red blood cell membrane. The technique employs laser interferometry and provides full-field quantitative topographical information of living cells with unprecedented stability. Integration with the mathematical model provides the specific material properties from individual cell membrane fluctuations: shear modulus of the membrane; bending modulus; and viscosity of the cytoplasm. Employing these methods, we have systemically studied the material properties of human red blood cells altered by various pathophysiological conditions: morphological transition of red blood cell; parasitization by the P. falciparum parasites; and metabolic remodeling of the membrane driven by Adenosine-5'- triphosphate (ATP). We envision that this investigation could offer a means to link cell membrane fluctuations with the pathological conditions that lead to human disease states by quantitatively providing the alternation in material properties. A clear understanding of the mechanical alteration of red blood cells is important to studying the human diseases which cause their infection.Ph.D

Micro/nano devices for blood analysis

[Excerpt] The development of microdevices for blood analysis is an interdisciplinary subject that demandsan integration of several research fields such as biotechnology, medicine, chemistry, informatics, optics,electronics, mechanics, and micro/nanotechnologies.Over the last few decades, there has been a notably fast development in the miniaturization ofmechanical microdevices, later known as microelectromechanical systems (MEMS), which combineelectrical and mechanical components at a microscale level. The integration of microflow and opticalcomponents in MEMS microdevices, as well as the development of micropumps and microvalves,have promoted the interest of several research fields dealing with fluid flow and transport phenomenahappening at microscale devices. [...

Coarse-grained modelling of blood cell mechanics

This thesis concerns development of mechanically realistic in silico representations of human blood cells using coarse-grained molecular dynamics (CGMD), ultimately building a new model for a lymphocyte-class white blood cell (WBC). This development is approached successively, evaluated through simulation of experimental testing methods common to past in vitro studies on blood cell mechanics. Considering both their biophysical simplicity and the extensive associated literature, the red blood cell (RBC) is first considered. As a foundation, I thus used the CGMD RBC model of Fu et al. [Lennard-Jones type pair-potential method for coarse-grained lipid bilayer membrane simulations in LAMMPS, Fu et al., Comput. Phys. Commun., 210, 193-203 (2017)]. Chapter 3 establishes implementation of this model, and in silico implementations of the three chosen testing methods. In doing so, the first quantitative assessment of the "miniature cell" approach is conducted - being the down-scaling of the physical cell size to make feasible simulation times, as was done in the original article presenting the model. The RBC model is then used as a foundation from which to develop a new whole-cell WBC lymphocyte model. This is approached sequentially. Firstly (Chapter 4), the morphology and mechanics relevant to the existing RBC model are adapted to those of a lymphocyte. As such, a quasi-spherical morphology is induced, and elastic membrane-associated parameters brought in line with the literature on isolated lymphocytes in vitro. A semi-rigid nucleus is then added to the cell interior, again parameterised to produce elastic properties consistent with the literature. These developments produce a cell having macroscopic mechanical properties much more consistent with a WBC, with an "optimal" parameterisation established. After the membrane and nucleus, the entity most influential to the mechanics of nucleated cells (such as WBC) is their complex intracellular actin-based cytoskeleton (CSK). Therefore, Chapter 5 attempts to represent such a system within our new lymphocyte model. This is approached in three successive stages, assessed against recognised CSK mechanical properties, in particular those also common to soft glassy materials. As such, a novel CSK representation is developed, inspired as a discretisation of soft glassy rheology (SGR). It is proposed that the resulting system has characteristics comparable to having undergone a glass-like transition, as relatable to a real CSK. Therefore, the resulting lymphocyte model may lay a foundation for future development towards mechanically accurate representations of other cells - in particular, a circulating tumour cell

Flow behavior of chain and star polymers and their mixtures

Star-shaped polymers show a continuous change of properties from flexible linear chains to soft colloids, as the number of arms is increased. to investigate the effect of macromolecular architecture on the flow properties, we employ computer simulations of single chain and star polymers as well as of their mixtures under poiseuille flow. hydrodynamic interactions are incorporated through the multi-particle collision dynamics (mpcd) technique, while a bead-spring model is used to describe the polymers. for the ultradilute systems at rest, the polymers are distributed uniformly in the slit channel, with a weak dependence on their number of arms. once flow is applied, however, we find that the stars migrate much more strongly towards the channel center as the number of arms is increased. in the star-chain mixtures, we find a flow-induced separation between stars and chains, with the stars located in the channel center and the chains closer to the walls. in order to identify the origin of this flow-induced partitioning, we conduct additional simulations without hydrodynamic interactions, and find that the observed cross-stream migration originates from a combination of wall-induced hydrodynamic lift forces and viscoelastic effects. the results from our study give valuable insights for designing microfluidic devices for separating polymers based on their architecture