Transport of flexible fibers in confined micro-channels

TL;DR

This study combines experiments and simulations to analyze how flexible fibers deform when transported in confined micro-channels, revealing the relationship between force distribution, fiber bending, and confinement effects.

Contribution

It provides a quantitative characterization of fiber deformation in confined flows, linking bending to the elasto-viscous number through combined experimental and numerical approaches.

Findings

Fiber bending is proportional to the elasto-viscous number.

Confinement significantly influences fiber deformation.

Experimental and simulation results are in good agreement.

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.