Flow-induced translocation of vesicles through a narrow pore

Transport and clogging dynamics of flexible rods in pore constrictions

The transport and clogging behavior of flexible particles in confined flows is a complex interplay between elastic and hydrodynamic forces and wall interactions. While the motion of non-spherical particles in unbounded flows is well understood, their behavior in confined spaces remains less explored. This study introduces a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach to investigate the transport and clogging dynamics of flexible rod-shaped particles in confined pore constrictions. The spatio-temporal analysis reveals the influence of the rod's initial conditions and flexibility on its transport dynamics through a pore constriction. The simulation results demonstrate an increase in the lateral drift of the rod upon exiting the pore that can be scaled with channel height confinement. The clogging dynamics are explored based on hydrodynamic and mechanical forces, unveiling conditions for mechanical clogging through sieving. The developed method allows for the deconvolution of the forces that contribute to particle trajectories in confined flow, which is highly relevant in particle separation processes, fibrous-shaped virus filtration, biological flows, and related applications. The method is embedded into the open-source CFDEM framework, facilitating future extensions to explore multiple particle dynamics, intermolecular forces, external influences, and complex geometries.

Numerical investigation on flow-induced wall shear stress variation of metastatic cancer cells in lymphatics with elastic valves

Hematogenous metastasis occurs when cancer cells detach from the extracellular matrix in the primary tumor into the bloodstream or lymphatic system. Elucidating the response of metastatic tumor cells in suspension to the flow conditions in lymphatics with valves from a mechanical/fluidic perspective is necessary. A physiologically relevant computational model of a lymphatic vessel with valves was constructed using fully coupled fluid-cell-vessel interactions to investigate the effects of lymphatic vessel contractility, valve properties, and cell size and stiffness on the variations in magnitude and gradient of the flow-induced wall shear stress (WSS) experienced by suspended tumor cells. Results indicated that the maximum WSSmax increased with the increments in cell diameter, vessel contraction amplitude, and valve stiffness. The decrease in vessel contraction period and valve aspect ratio also increased the maximum WSSmax. The influence of the properties of the valve on the WSS was more significant among the factors mentioned above. The maximum WSSmax acting on the cancer cell when the cell reversed the direction of its motion in the valve region increased by 0.5-1.4 times that before the cell entered the valve region. The maximum change in WSS was in the range of 0.004-0.028 Pa/µm depending on the factors studied. They slightly exceeded the values associated with breast cancer cell apoptosis. The results of this study provide biofluid mechanics-based support for mechanobiological research on the metastasis of metastatic cancer cells in suspension within the lymphatics.

Universality in the Dynamics of Vesicle Translocation through a Hole

We analyze the translocation process of a spherical vesicle, made of a membrane and incompressible fluid, through a hole smaller than the vesicle size, driven by pressure difference ΔP. We show that such a vesicle shows certain universal characteristics, which are independent of the details of the membrane elasticity: (i) there is a critical pressure ΔP_c below which no translocation occurs; (ii) ΔP_c decreases to zero as the vesicle radius R₀ approaches the hole radius a, satisfying the scaling relation ΔP_c ∼ (R₀ - a)^3/2; and (iii) the translocation time τ diverges as ΔP decreases to ΔP_c, satisfying the scaling relation τ ∼ (ΔP - ΔP_c)^-1/2.

Flow-driven competition between two capsules passing through a narrow pore

By incorporating a distance function into the finite element simulation, we investigate the flow-driven competition between two soft capsules passing through a narrow pore, employing the arbitrary Lagrangian-Eulerian formulation to satisfy the boundary conditions for fluid flow and capsule deformation. In our simulations, the motion and deformation of the capsules can be described in an intuitive manner, and the order in which capsules of different sizes pass through a pore can be clearly determined. Meanwhile, when the capsules are near the narrow pore, the change of the flow field is also very interesting and can be expressed intuitively. It is shown that, driven by the Poiseuille flow, the larger capsule has a stronger tendency to pass through the pore than the small one, which can be attributed to the greater resistance and the volume advantage of the larger capsule. In addition, we demonstrate that this tendency can be reversed by changing the inlet velocity and setting the initial position of the smaller capsule closer to the axis of the pore. And as long as the large one passes through first, the small one will offset the axis to the same orientation as the initial, while the large one always moves along the axis.

Transport and Retention Behaviors of Deformable Polyacrylamide Microspheres in Convergent-Divergent Microchannels

Knowledge of the transport and retention behaviors of soft deformable particles on the microscale is essential for the design, evaluation, and application of engineered particle materials in the fields of energy, environment, and sustainability. Emulated convergent-divergent microchannels were constructed and used to investigate the transport and retention behaviors of soft deformable polyacrylamide microspheres at various conditions. Five different types of transport and retention patterns, i.e., surface deposition, smooth passing, direct interception, deforming remigration, and rigid blockage, are observed. Flow resistance variation characteristics caused by different patterns were quantitatively analyzed. Effects of flow rate, pore-throat size, particle size, and injection concentration on transport and retention patterns have been studied, and transport and retention pattern maps are presented and discussed.