Relationship between transit time and mechanical properties of a cell through a stenosed microchannel

Deformation-induced phase separation of active vesicles

Many active materials, such as bacteria and cells, are deformable. Deformability significantly affects their collective behaviors and movements in complex environments. Here, we introduce a two-dimensional deformable active vesicle (DAV) model to emulate cell-like deformable active matter, wherein the deformability can be continuously adjusted. We find that changes in deformability can induce phase separation of DAVs. The system can transition between a homogeneous gas state, a coexistence of gas and liquid, and a coexistence of gas and solid. The occurrence of deformation-induced phase separation is accompanied by nonmonotonic changes in effective concentration, particle size and shape. Moreover, the degree of deformability also impacts the motility and stress within the dense phase following phase separation. Our results offer new insights into the role of deformability in the collective behavior of active matter.

Numerical analysis of blood flow through stenosed microvessels using a multi-phase model

Blood flow in arterioles have attracted considerable research attention due to their clinical implications. However, the fluid structure interaction between red blood cells and plasma in the blood poses formidable difficulty to the computational efforts. In this contribution, we seek to represent the red blood cells in the blood as a continuous non-Newtonian phase and construct a multi-phase model for the blood flow in microvessels. The methods are presented and validated using a channel with sudden expansion. And the resulting blood flow inside a stenosed microvessel is investigated at different inlet velocity amplitudes and hematocrits. It is show that the increase of both inlet velocity amplitude and inlet hematocrit leads to longer and thicker cell-rich layer downstream the stenosis. Besides, it is found that the maximum values of wall shear stress scales up with inlet velocity amplitudes and hematocrits. These results show the validity of the proposed computational model and provide helpful insights into blood flow behaviors inside stenosed vessels.

Experimental measurement and numerical modeling of deformation behavior of breast cancer cells passing through constricted microfluidic channels

During the multistep process of metastasis, cancer cells encounter various mechanical forces which make them deform drastically. Developing accurate in-silico models, capable of simulating the interactions between the mechanical forces and highly deformable cancer cells, can pave the way for the development of novel diagnostic and predictive methods for metastatic progression. Spring-network models of cancer cell, empowered by our recently proposed identification approach, promises a versatile numerical tool for developing experimentally validated models that can simulate complex interactions at cellular scale. Using this numerical tool, we presented spring-network models of breast cancer cells that can accurately replicate the experimental data of deformation behavior of the cells flowing in a fluidic domain and passing narrow constrictions comparable to microcapillary. First, using high-speed imaging, we experimentally studied the deformability of breast cancer cell lines with varying metastatic potential (MCF-7 (less invasive), SKBR-3 (medium-high invasive), and MDA-MB-231 (highly invasive)) in terms of their entry time to a constricted microfluidic channel. We observed that MDA-MB-231, that has the highest metastatic potential, is the most deformable cell among the three. Then, by focusing on this cell line, experimental measurements were expanded to two more constricted microchannel dimensions. The experimental deformability data in three constricted microchannel sizes for various cell sizes, enabled accurate identification of the unknown parameters of the spring-network model of the breast cancer cell line (MDA-MB-231). Our results show that the identified parameters depend on the cell size, suggesting the need for a systematic procedure for identifying the size-dependent parameters of spring-network models of cells. As the numerical results show, the presented cell models can simulate the entry process of the cell into constricted channels with very good agreements with the measured experimental data.

Dynamics and rheology of vesicles under confined Poiseuille flow

The rheological behavior and dynamics of a vesicle suspension, serving as a simplified model for red blood cells, are explored within a Poiseuille flow under the Stokes limit. Investigating vesicle response has led to the identification of novel solutions that complement previously documented forms like the parachute and slipper shapes. This study has brought to light the existence of alternative configurations, including a fully off-centered form and a multilobe structure. The study unveils the presence of two distinct branches associated with the slipper shape. One branch arises as a consequence of a supercritical bifurcation from the symmetric parachute shape, while the other emerges from a saddle-node bifurcation. Notably, the findings are represented through diagrams that display data collapsing harmoniously based on a combination of independent dimensionless parameters. Delving into the rheological implications, a remarkable observation emerges: the normalized viscosity (i.e. similar to intrinsic viscosity) exhibits a non-monotonic trend as a function of vesicle concentration. Initially, the normalized viscosity diminishes as the concentration increases, followed by a subsequent rise at higher concentrations. Noteworthy is the presence of a minimum value in the normalized viscosity at lower concentrations, aligning well with the concentrations observed in microcirculation scenarios. The intricate behavior of the normalized viscosity can be attributed to a delicate spatial arrangement within the suspension. Importantly, this trend echoes the observations made in a linear shear flow scenario, thereby underscoring the universality of the rheological behavior for confined suspensions.

Mechano-immunology in microgravity

Life on Earth has evolved to thrive in the Earth's natural gravitational field; however, as space technology advances, we must revisit and investigate the effects of unnatural conditions on human health, such as gravitational change. Studies have shown that microgravity has a negative impact on various systemic parts of humans, with the effects being more severe in the human immune system. Increasing costs, limited experimental time, and sample handling issues hampered our understanding of this field. To address the existing knowledge gap and provide confidence in modelling the phenomena, in this review, we highlight experimental works in mechano-immunology under microgravity and different computational modelling approaches that can be used to address the existing problems.

Design and fabrication of aspiration microfluidic channel for oocyte characterization

The development potential for oocytes can be predicted by their mechanical properties. One important parameter that is measured to calculate oocyte hardness is Cortical Tension (CT). In this work, for the first time, we present the design, simulation, and fabrication of a new aspiration microfluidic chip to measure the CT of oocytes and then predict their maturation capability in the Germinal Vesicle (GV) stage. This high-performance technique facilitates oocyte characterization and is a promising alternative to traditional methods such as MicroPipette Aspiration (MPA). The proposed technique involves considerably simpler operation, less specialized equipment, and less technical skill than MPA. The proposed microfluidic channel also promises faster measurements. It is shown that in order to completely continue the growth process of oocytes in GV stage, the CT should be in a certain range: very low or very high CTs lead to unsuccessful growth. The obtained results show that 79% of oocytes with the CT between 1.5 and 3 nN/μm reach the Metaphase II (MII) stage, whereas the growth for 78% of oocytes with the CT less than 1.5 nN/μm or higher than 3 nN/μm stops at the GV or Germinal Vesicle Break Down (GVBD) stages. Another property, k_vis, that points to the viscous behavior of oocytes is also measured. It is seen that 80% of GV oocytes with the k_vis values between 15 and 30 k Pa s/m reach the MII stage.

A systematic approach for developing mechanistic models for realistic simulation of cancer cell motion and deformation

Understanding and predicting metastatic progression and developing novel diagnostic methods can highly benefit from accurate models of the deformability of cancer cells. Spring-based network models of cells can provide a versatile way of integrating deforming cancer cells with other physical and biochemical phenomena, but these models have parameters that need to be accurately identified. In this study we established a systematic method for identifying parameters of spring-network models of cancer cells. We developed a genetic algorithm and coupled it to the fluid-solid interaction model of the cell, immersed in blood plasma or other fluids, to minimize the difference between numerical and experimental data of cell motion and deformation. We used the method to create a validated model for the human lung cancer cell line (H1975), employing existing experimental data of its deformation in a narrow microchannel constriction considering cell-wall friction. Furthermore, using this validated model with accurately identified parameters, we studied the details of motion and deformation of the cancer cell in the microchannel constriction and the effects of flow rates on them. We found that ignoring the viscosity of the cell membrane and the friction between the cell and wall can introduce remarkable errors.

Non-invasive acquisition of mechanical properties of cells via passive microfluidic mechanisms: A review

The demand to understand the mechanical properties of cells from biomedical, bioengineering, and clinical diagnostic fields has given rise to a variety of research studies. In this context, how to use lab-on-a-chip devices to achieve accurate, high-throughput, and non-invasive acquisition of the mechanical properties of cells has become the focus of many studies. Accordingly, we present a comprehensive review of the development of the measurement of mechanical properties of cells using passive microfluidic mechanisms, including constriction channel-based, fluid-induced, and micropipette aspiration-based mechanisms. This review discusses how these mechanisms work to determine the mechanical properties of the cell as well as their advantages and disadvantages. A detailed discussion is also presented on a series of typical applications of these three mechanisms to measure the mechanical properties of cells. At the end of this article, the current challenges and future prospects of these mechanisms are demonstrated, which will help guide researchers who are interested to get into this area of research. Our conclusion is that these passive microfluidic mechanisms will offer more preferences for the development of lab-on-a-chip technologies and hold great potential for advancing biomedical and bioengineering research studies.

Determination of Dielectric Properties of Cells using AC Electrokinetic-based Microfluidic Platform: A Review of Recent Advances

Cell dielectric properties, a type of intrinsic property of cells, can be used as electrophysiological biomarkers that offer a label-free way to characterize cell phenotypes and states, purify clinical samples, and identify target cancer cells. Here, we present a review of the determination of cell dielectric properties using alternating current (AC) electrokinetic-based microfluidic mechanisms, including electro-rotation (ROT) and dielectrophoresis (DEP). The review covers theoretically how ROT and DEP work to extract cell dielectric properties. We also dive into the details of differently structured ROT chips, followed by a discussion on the determination of cell dielectric properties and the use of these properties in bio-related applications. Additionally, the review offers a look at the future challenges facing the AC electrokinetic-based microfluidic platform in terms of acquiring cell dielectric parameters. Our conclusion is that this platform will bring biomedical and bioengineering sciences to the next level and ultimately achieve the shift from lab-oriented research to real-world applications.

Fluid shear stress coupled with narrow constrictions induce cell type-dependent morphological and molecular changes in SK-BR-3 and MDA-MB-231 cells

Cancer mortality mainly arises from metastases, due to cells that escape from a primary tumor, circulate in the blood as circulating tumor cells (CTCs), permeate across blood vessels and nest in distant organs. It is still unclear how CTCs overcome the harsh conditions of fluid shear stress and mechanical constraints within the microcirculation. Here, a minimal model of the blood microcirculation was established through the fabrication of microfluidic channels comprising constrictions. Metastatic breast cancer cells of epithelial-like and mesenchymal-like phenotypes were flowed into the microfluidic device. These cells were visualized during circulation and analyzed for their dynamical behavior, revealing long-lived plastic deformations and significant differences in biomechanics between cell types. γ-H2AX staining of cells retrieved post-circulation showed significant increase of DNA damage response in epithelial-like SK-BR-3 cells, while gene expression analysis of key regulators of epithelial-to-mesenchymal transition revealed significant changes upon circulation. This work thus documents first results of the changes at the cellular, subcellular and molecular scales induced by the two main mechanical stimuli arising from circulatory conditions, and suggest a significant role of this still elusive step of the metastatic cascade in cancer cells heterogeneity and aggressiveness.

Red blood cell distribution in a microvascular network with successive bifurcations

Nonproportional RBC distribution is an important characteristic in microvascular networks, which can result in heterogeneity of oxygen supply that may cause ischemic death in severe cases. In this paper, we perform three-dimensional numerical simulations of a large number of RBCs in a microvascular network, by using a hybrid method of smoothed dissipative particle dynamic and immersed boundary method. The distribution of multiple RBCs in a T-bifurcation is first simulated as a validation study, and a reasonable agreement is observed both qualitatively and quantitatively on the RBC flux between our results and the previously published numerical and empirical results. Next, the distribution of a large number of RBCs in a microvascular network is investigated, including the effects of cell deformability, aggregation and tube hematocrit. The simulation results indicate that decreased deformability and increased aggregation strength have a similar effect on the RBC distribution: the large RBC flux becomes larger, but the small becomes smaller. A high hematocrit also causes a similar phenomenon that the RBCs are more apt to flow into a high RBC-flux branch, because they are arranged compactly into a rouleaux and difficultly broken up at a high hematocrit. These results imply that lower cell deformability, stronger aggregation or higher tube hematocrit would be conducive to the phase separation of hematocrit and plasma skimming processes in microcirculation.

Flow-induced translocation of vesicles through a narrow pore

We use finite element method to investigate the flow-induced translocation of vesicles through a narrow pore from a dynamic point of view. In order to complete the coupling between fluid flow and the vesicle membranes, we employ the fluid-structure interactions with the arbitrary Lagrangian-Eulerian method. Our results demonstrate that the vesicle shows similar shape change from bullet-like to dumbbell-like, dumbbell-like to bulb-like, and bulb-like to parachute-like if it is pushed by flow field to pass through a narrow pore smaller than its size. We further find that the strain energy exhibits a higher peak and a lower peak in the whole translocation process, where the higher peak corresponds to the dumbbell-like shape and the lower peak corresponds to the parachute-like shape due to more stretching of the membrane for the dumbbell-like shape than that of the parachute-like shape. The translocation time of the vesicle from one side to the other side of the narrow pore decreases with the increase of inlet velocity, but the strain energy exhibits an increase, which implies that the vesicle needs more time to complete the translocation with the lower inlet velocity, but the requirement for the mechanical properties of the membrane is lower. Our work answers the mapping between the positions of the vesicles and deformed states with the stress distribution and change of strain energy, which can provide helpful information on the utilization of vesicles in pharmaceutical, chemical, and physiological processes.

Photosensitive Schottky barrier diode behavior of a semiconducting Co(iii)–Na complex with a compartmental Schiff base ligand

The opto-electronic properties of an X-ray characterized, end-to-end azide bridged cobalt(iii)–sodium complex, [(N₃)CoLNa(N₃)]_n, have been investigated in detail. The complex is found to be a direct semiconductor material as confirmed by determining the band gap of this complex by experimental as well as theoretical studies. The complex has also been used to construct a photosensitive Schottky device. Optical conductivity, calculated from the DFT study, has been used to analyze how the conductivity of the material changes upon illumination. The electrical conductivity and concomitantly, the photoconductivity of the material increase as a consequence of photon absorption.

The opto-electronic properties of a cobalt(iii)–sodium complex have been studied with the help of both experimental and theoretical investigation. The complex has also been used to fabricate an effective photosensitive Schottky device.

Numerical design of a microfluidic chip for probing mechanical properties of cells

Microfluidic chips have been widely used to probe the mechanical properties of cells, which are recognized as a promising label-free biomarker for some diseases. In our previous work (Ye et al., 2018), we have studied the relationships between the transit time and the mechanical properties of a cell flowing through a microchannel with a single constriction, which potentially forms a basis for a microfluidic chip to measure cell's mechanical properties. Here, we investigate this microfluidic chip design and examine its potential in performances. We first develop the simultaneous dependence of the transit time on both the shear and bending moduli of a cell, and then examine the chip sensitivity with respect to the cell mechanical properties while serializing a single constriction along the flow direction. After that, we study the effect of the flow velocity on the transit time, and also test the chip's ability to identify heterogeneous cells with different mechanical properties. The results show that the microfluidic chip designed is capable of identifying heterogeneous cells, even when only one unhealthy cell is included. The serialization of chip can greatly increase the chip sensitivity with respect to the mechanical properties of cells. The flow with a higher velocity helps in not only promoting the chip throughput, but also in providing more accurate transit time measurements, because the cell prefers a symmetric deformation under a high velocity.

Nano- and microscale mechanical properties of erythrocytes in hereditary spherocytosis

Hereditary spherocytosis (HS), an erythrocyte membranopathy, is a heterogeneous disease, even at the level of the erythrocyte population. The paper aims at studying the mechanical properties (the Young's modulus, median and RMS roughness of friction force maps; fractal dimension, lacunarity and spatial distribution parameters of lateral force maps) of the cell surface layer of the erythrocytes of two different morphologies (discocytes and spherocytes) in HS using atomic force microscopy. The results of spatial-spectral and fractal analysis showed that the mechanical property maps of the HS spherocyte surface were more structurally homogeneous compared to the maps of HS discocytes. HS spherocytes also had a reduced RMS roughness and lacunarity of the mechanical property maps. The Young's modulus and averaged friction forces over the microscale HS spherocyte surface regions were approximately 20% higher than that of HS discocytes. The revealed significant difference at the nano- and microscales in the structural and mechanical properties of main (discoidal and spheroidal) morphological types of HS erythrocytes can potentially cause blood flow disturbance in the vascular system in HS.