Microgel Translocation Through Narrow Capillaries

TL;DR

This study investigates how soft microgels move through narrow capillaries, revealing a critical size limit and the roles of elasticity and network structure in determining whether the gel can pass through or becomes stuck.

Contribution

The paper introduces a combined simulation and theoretical framework to identify the size threshold and mechanical factors influencing microgel translocation in confined geometries.

Findings

A critical capillary diameter $d_c$ prevents microgel entry.

Gel mobility depends on applied force and network topology.

Densification causes stalling beyond a force cutoff.

Abstract

The transport of soft viscoelastic gels through confined geometries underlies critical processes in biomedical, biological, and industrial systems. Here, we examine the translocation of a spherical microgel through a narrow capillary whose diameter is smaller than the equilibrium gel size. Using coarse-grained molecular dynamics simulations in tandem with mean-field theory and mechanical analysis, we uncover a critical threshold diameter $d_c$ below which the microgel cannot enter, regardless of the applied pressure. This geometric limit emerges from the interplay between gel elasticity and its internal network connectivity, captured quantitatively by a graph-theoretic model. We construct a phase diagram in the parameter space of tube diameter $d$, applied force $f_g$, and gel stiffness $Y$ (Young's modulus), which delineates the regimes of successful translocation and mechanical arrest. Under negligible wall friction, gel mobility scales with the applied force; however, beyond a cutoff set by the network topology, progressive densification in the constriction stalls the microgel. Our results reveal the mechanical and topological determinants of soft-gel transport in confinement and provide predictive guidelines for engineering gel-based systems in microfluidics, drug delivery, and tissue-level filtration.