Srikanth Vedantam

We present a dissipative particle dynamics (DPD) study of the deformation of capsules in microchannels. The strain in the membrane during this deformation causes the formation of temporary pores, which is termed mechanoporation. Mechanoporation is being considered as a means by which intracellular delivery of a broad range of cargo can be facilitated. In this work, we examine the strain distribution on the capsule membrane during transport of the capsule in converging-diverging microchannels of different constriction widths. The pore density is correlated to the strain in the membrane. We find that the highest strains and, consequently, the highest pore densities occur at intermediate channel widths. This occurs due to a competition of the bending of the membrane and fluid shear stresses in the flow.

Thin deformable membranes are encountered in a number of microfluidics-based applications. These are often employed for enhancing sorting, mixing, cross-diffusion transport, etc. Microfluidic systems with deformable membranes can be better understood by employing simple models and efficient computational procedures. In this paper, we present a dissipative particle dynamics model to simulate the interaction between a deformable membrane and fluid flow in a two-dimensional microchannel. The membrane is modeled as a bead-spring system with both extensional and torsional springs to simulate extensional stiffness and bending rigidity, respectively. By performing detailed simulations on a membrane pinned at both ends and oriented parallel to the flow, we observe different steady state conformations. These membrane deflections are found to be relatively large for low bending stiffnesses and small for high stiffnesses. The membrane was found to exhibit a simple bowing out mode for high stiffness values and more complex conformations at lower stiffnesses.

The hydrodynamics of flow through two-dimensional parallel-plate microchannels with periodic hydrophobic strips under finite Reynolds numbers is studied using dissipative particle dynamics simulations. The hydrophobic and hydrophilic regions are modeled using partial-slip and no-slip boundary conditions, respectively. We first consider channels with symmetric hydrophobic strips on both walls. It was observed that the volume flow rate through the channel is nonlinearly dependent on the area fraction of the hydrophobic strips. Next, we study flow in an antisymmetric channel in which the hydrophobic strips on the two channel walls are staggered with an axial offset. We observe that, in contrast to the symmetric channels, the presence of antisymmetric strips cause a finite velocity component towards the center of the channel. This cross-stream velocity field may potentially prove useful for separating second-phase particles or enhancing mixing in such microchannels.