Analysis of micro-fluidic tweezers in the Stokes regime

TL;DR

This paper uses mathematical modeling to explain how nanowire fluidic tweezers capture and manipulate micro-objects in the Stokes flow regime, providing insights into the flow dynamics and capture mechanisms.

Contribution

It introduces a regularized Stokeslet-based model to analyze nanowire tumbling and particle interactions, clarifying the capture mechanism in microfluidic tweezers.

Findings

Flow structure and capture regions depend on particle size and tumbling rate.

Pure kinematic effects can explain particle capture and transport.

Capture regions relate to stagnation points in the flow field.

Abstract

Nanowire fluidic tweezers have been developed to gently and accurately capture, manipulate and deliver micro objects. The mechanism behind the capture and release process has not yet been well explained. Utilizing the method of regularized Stokeslet, we study a cylindrical nanowire tumbling and interacting with spherical particles in the Stokes regime. The capture phenomenon observed in experiments is reproduced and illustrated with the trajectories of micro-spheres and fluid tracers. The flow structure and the region of capture are quantitatively examined and compared for different sizes of particles, various tumbling rates, and dimensions of the tweezers. We find that pure kinematic effects can explain the mechanism of capture and transport of particles. We further reveal the relation between the capture region and stagnation points in the displacement field , i.e., the displacement for tracer particles in the moving frame within one rotation of the wire.