Transport of flexible fibers in confined microchannels

Abstract

When transported in confined geometries rigid fibers show interesting transport dynamics induced by friction with the top and bottom walls. Fiber flexibility causes an additional coupling between fiber deformation and transport and is expected to lead to more complex dynamics. A first crucial step for their understanding is the characterization of the deformed fiber shape. Here we characterize this shape for a fiber transported in a confined plug flow perpendicular to the flow direction using a combination of microfluidic experiments and numerical simulations. In the experiments, size, initial orientation, and mechanical properties of the fibers are controlled using micro-fabrication techniques and in-situ characterization methods.The numerical simulations use modified Brinkman equations as well as full 3D simulations. We show that the bending of a perpendicular fiber results from the force distribution acting on the elongated object and is proportional to the elasto-viscous number, comparing viscous to elastic forces. We quantitatively characterize the influence of the confinement on the fiber deformation. The precise understanding of the deformation of a flexible fiber in a confined geometry can also be used in future to understand the deformation and transport of more complex deformable particles in confined flows, as for example vesicles or red blood cells. arXiv:1807.05158v1 [physics.flu-dyn]

Dynamics of Flexible Fibers in Viscous Flows and Fluids

“…The fiber thus creates a flow perturbation inducing an inhomogeneous force distribution along the fiber. [15] have evaluated the force distribution as a function of fiber confinement using modified Brinkman equations. The resulting fiber shapes are found to be in good agreement with experimental findings ( [15]).…”

“…[15] have evaluated the force distribution as a function of fiber confinement using modified Brinkman equations. The resulting fiber shapes are found to be in good agreement with experimental findings ( [15]). The coupling between fiber deformation, drift, and interaction with the side walls ( [92]) leads to complex trajectories and finally a preferred alignment with the flow direction ( Fig.…”

“…The color scale indicates polymer stretching. (g) Trajectory of a flexible polymeric fiber confined by the top and bottom walls of a microchannel,[15]. (h) Simulations of the random walk of a flexible filament across a cellular flow,[150].…”

Universal motion of mirror-symmetric microparticles in confined Stokes flow

“…All three modes of motion, namely, rotation and streamwise and cross-streamwise translation, are also present when an asymmetric disk dimer is far away from any side walls as demonstrated by Uspal, Eral, and Doyle ( 22 ). Evidently, screened hydrodynamic interactions give rise to nontrivial behavior not only in particle ensembles ( 40 – 44 ), but also in single-particle systems with broken symmetry ( 45 – 51 ). A first step toward the development of low-cost flow separators requires understanding the relation between the geometry of one such particle and its trajectory in confined Stokes flow.…”

Microfluidic In-Situ Measurement of Poisson’s Ratio of Hydrogels

“…Slabs of hydrogel with controlled geometry and position were directly fabricated inside the micro-channel using microscope-based photolithography [13]. This method has been extensively detailed in previous works [13][14][15][16][17][18][19], and just the essential steps are detailed here and schematically represented in Figure 1. The channel, filled with an oligomer solution and a photo-initiator, is exposed to a pulse of UV light of controlled duration.…”