Transient dynamics of an elastic capsule in a microfluidic constriction

Area of Science:

• Fluid Dynamics
• Biophysics
• Computational Mechanics

Background:

• Understanding micro-scale fluid dynamics is crucial for biological systems.
• Elastic capsules and droplets exhibit complex behaviors in confined flows.
• Transient dynamics and deformation are key to capsule transport in microchannels.

Purpose of the Study:

• To computationally investigate the transient dynamics of elastic capsules versus droplets in a microchannel with a constriction.
• To analyze capsule deformation, velocity, and pressure drop under varying conditions.
• To elucidate the mechanisms governing non-tank-treading transient capsule dynamics.

Main Methods:

• Computational fluid dynamics simulations.
• Analysis of capsule deformation and flow patterns.
• Comparison of capsule and droplet behavior in a square microchannel with a rectangular constriction.

Main Results:

• Capsules exhibit rich deformation, elongating at constriction entrance and flattening at exit.
• Larger capsules experience higher pressure differences and longer transit times due to flow blocking.
• Capsule viscosity impacts deformation, but viscosity ratio has minimal effect on velocity and pressure drop.
• Unlike droplets, capsules generate a positive pressure difference even at low viscosity.

Conclusions:

• Capsule deformation is governed by normal stresses, with increased viscosity reducing deformation.
• Limited inner circulation in capsules affects their velocity and pressure drop differently than droplets.
• Findings suggest high cytoplasmic viscosity in erythrocytes does not impede motion in capillaries.